¿Pueden resumir brevemente la relación entre nutrición e inmunidad? 

Hemos sabido durante mucho tiempo que la nutrición está estrechamente relacionada con la inmunidad y con el riesgo y gravedad de infecciones. Los individuos mal nutridos tienen un mayor riesgo de diversas infecciones bacterianas y virales, entre otras. Por el contrario, las infecciones crónicas o severas conducen a trastornos nutricionales o empeoran el estado nutricional de las personas afectadas. Por lo tanto, es imperativo que todos prestemos atención a nuestra dieta y estado nutricional durante la actual pandemia de COVID-19. Además, el curso clínico de la enfermedad de COVID-19 tiende a ser más grave entre las personas mayores y entre las personas con enfermedades crónicas, como la diabetes, la hipertensión, y el cáncer, que están parcialmente relacionados con la nutrición. [1] Aunque todavía no se dispone de datos, las co-infecciones, como el VIH/SIDA, también pueden estar asociadas con resultados más graves, y una nutrición óptima desempeña un rol importante en el mantenimiento de la salud entre las personas con tales infecciones.

Ciertamente, consumir dietas de buena calidad siempre es deseable, y esto es particularmente importante durante la pandemia de COVID-19. Una dieta saludable, como se muestra en El Plato Para Comer Saludable, hace hincapié en las frutas, verduras, cereales integrales, legumbres y nueces, el consumo moderado de pescado, alimentos lácteos y aves, y la ingesta limitada de carne roja y procesada, carbohidratos refinados, y azúcar. Las grasas añadidas deben ser principalmente aceites líquidos como de oliva, canola, o el aceite de soja.  Dicha dieta proporcionará cantidades adecuadas de macronutrientes saludables y minerales y vitaminas esenciales. Comer proteínas, grasas y carbohidratos de alta calidad puede ayudar a mantener un peso saludable y un buen estado metabólico; este no es un momento para dietas altamente restrictivas. Si alguien desarrolla una infección COVID-19, es importante comer lo suficiente de estas calorías saludables para prevenir la pérdida de peso no intencional. Las cantidades adecuadas de minerales y vitaminas proporcionadas por una dieta saludable ayudan a asegurar un número suficiente de células del sistema inmune y de anticuerpos, los cuales son importantes a medida que el cuerpo desarrolle una respuesta a las infecciones.

Aunque no tenemos datos sobre factores nutricionales en relación al riesgo y la gravedad de COVID-19, ¿cuáles son algunos ejemplos de evidencia que existe sobre nutrición e infección que serían importante considerar?

Hay muchos estudios que evalúan la ingesta de nutrientes específicos en relación con otras infecciones. Para dar algunos ejemplos:

• El zinc es un componente presente en muchas enzimas y factores de transcripción en las células de todo el cuerpo, y los niveles inadecuados de zinc limitan la capacidad del individuo para desarrollar una respuesta inmune adecuada a las [2] Múltiples meta-análisis y análisis agrupados de estudios clínicos aleatorizados han demostrado que la suplementación oral con zinc reduce la tasa de incidencia de infecciones agudas del tracto respiratorio en un 35%, acorta la duración de los síntomas similares a la gripe en aproximadamente 2 días, y mejora la tasa de recuperación. [3,4]. Estos estudios se llevaron a cabo en los Estados Unidos, así como en múltiples países de ingresos bajos y medianos como India, Sudáfrica, y Perú. La dosis de zinc en estos estudios varió de 20 mg/semana a 92 mg/día. La dosis no parece ser el principal promotor de la eficacia de la suplementación con zinc.
• La vitamina C es un cofactor de muchas Mejora la función de muchas enzimas en todo el cuerpo manteniendo sus iones metálicos en la forma reducida. También actúa como un antioxidante, limitando la inflamación y el daño del tejido asociado con las respuestas inmunológicas. [5] Se han llevado a cabo estudios clínicos aleatorizados en soldados, jóvenes y personas mayores en los Estados Unidos, la Unión Soviética, el Reino Unido y Japón que evalúan la eficacia de la vitamina C. En estos estudios, se demostró que la suplementación con vitamina C reduce significativamente la incidencia de infecciones del tracto respiratorio. [6] También se ha estudiado la eficacia de la vitamina C en pacientes hospitalizados en los Estados Unidos, Egipto e Irán, admitidos por una amplia variedad de condiciones incluyendo sepsis, complicaciones postoperatorias, quemaduras, contusiones pulmonares, y condiciones cardíacas. [7] Se demostró que la vitamina C reduce la duración de la estancia en la unidad de cuidados intensivos y la necesidad de ventilación mecánica en estos pacientes. [8] La dosis de vitamina C varió de 1-3 g/día, y la dosis no parece ser el principal promotor de la eficacia. Las dosis de vitamina C por encima de 2 g/día deben evitarse fuera de atención médica.
• La evidencia de varios estudios clínicos y estudios agrupados muestra que la suplementación con vitamina D reduce las probabilidades de desarrollar infecciones agudas del tracto respiratorio (la mayoría de las cuales se asume que se deben a viruses) en un 12% a un 75%. [9-12] Estos estudios incluyeron tanto la gripe estacional como la gripe pandémica causada por el virus H1N1 en el El efecto benéfico de la suplementación se observó en pacientes de todas las edades, y en personas con enfermedades crónicas pre-existentes. [13] Entre los infectados, los síntomas de la gripe fueron menores y la recuperación fue más temprana si habían recibido una dosis de vitamina D superior a 1,000 UI. [14] Los beneficios fueron relativamente mayores en individuos con deficiencia de vitamina D que en aquellos con niveles adecuados de vitamina D.
• Los adultos mayores tienden a ser deficientes de estos micronutrientes, y por lo tanto pueden obtener el mayor beneficio de la suplementación. [15,16]

Ustedes mencionan que una nutrición adecuada juega un rol importante en mantener la salud en personas con infecciones como VIH/SIDA. ¿Podrían comentar algo más al respecto?

Muchas infecciones agudas del tracto respiratorio suelen ser más severas en personas que viven con VIH/SIDA y otras deficiencias inmunológicas [17], y los esfuerzos para monitorear COVID-19 en estas poblaciones son importantes. La nutrición también juega un papel importante en esta categoría de personas. En primer lugar, la infección por VIH y la malnutrición tienden a coexistir. Conforme progresa la enfermedad, muchas personas que viven con VIH tienden a tener desnutrición. Algunos medicamentos para el VIH también pueden provocar enfermedades metabólicas. En segundo lugar, en personas con infección por VIH, un estado nutricional bajo y deficiencias de micronutrimentos empeoran la enfermedad por VIH y aumentan el riesgo de fallas en el tratamiento y muerte. Antes de que surgiera la terapia antirretroviral, los estudios demostraban que personas viviendo con VIH con dietas de alta calidad y mejor estado nutricional tendían a vivir por más tiempo y tenían menos complicaciones. Era menos probable que tuvieran anemia y tenían un conteo más alto de células CD4 (el conteo de células blancas sanguíneas que combaten la infección). Estudios clínicos aleatorizados y grandes estudios prospectivos en África y Asia han demostrado que el uso de multivitamínicos conduce a menos muertes y disminuye notablemente la progresión de la enfermedad [18-20]. Los resultados de estos estudios fueron consistentes sin importar si las personas infectadas con VIH recibían terapia antirretroviral o no. En los Estados Unidos, el consumo adecuado de vitaminas y minerales estaba asociado de igual manera a una reducción de la progresión de la enfermedad por VIH y mortalidad [21]. Por ello, una dieta de buena calidad y suplementación con multivitamínicos pueden contribuir a reducir el riesgo de infección por COVID-19 en personas con VIH y enfermedades similares.

¿Existe un papel para los suplementos nutricionales en la pandemia de COVID-19? 

Las encuestas dietéticas en Estados Unidos y en otros lugares muestran que la mayoría de las personas están consumiendo dietas que no cumplen con las recomendaciones nacionales- a menudo debido a la disponibilidad o precio- y dichas dietas pueden no proveer cantidades óptimas de vitaminas y minerales esenciales. Actualmente, es probable que la pandemia de COVID-19 ponga a muchos individuos en riesgo de inseguridad alimentaria y dificulte aún más el consumo de una dieta saludable. Esto se vuelve cada vez más probable si las estrategias para reducir la infección no consideran esfuerzos para garantizar la distribución y acceso efectivos de suministros esenciales, o si la pandemia afecta la productividad del sector agrícola.

Aunque no estamos al tanto de información de calidad sobre los efectos de suplementos nutricionales en el riesgo o gravedad de COVID-19, la evidencia existente indica que suplementos de varios nutrimentos puede reducir el riesgo o la gravedad de algunas infecciones virales, especialmente en personas con fuentes dietéticas inadecuadas. Por lo tanto, es prudente sugerir que se evite el consumo inadecuado de minerales y vitaminas, y los suplementos pueden ayudar a corregir esta situación. Algunos puntos importantes:

• Tomar un suplemento multivitamínico o multi-mineral estándar (RDA, recomendación diaria, por sus siglas en inglés) como una medida de seguridad nutricional es razonable. Estos suplementos son relativamente accesibles (un suministro para 6 meses debe costar menos de 40 dólares) y es una forma conveniente de llenar y mantener las reservas de micronutrimentos.
• Es especialmente importante mantener niveles adecuados de vitamina D. La vitamina D se produce normalmente en nuestra piel cuando se expone a la luz del sol, y durante el final del invierno y primavera los niveles de vitamina D en la sangre tienen a ser bajos debido a poca exposición solar. Permanecer en el interior reducirá aún más los niveles en sangre. Aunque en este momento no tenemos evidencia de que los suplementos de vitamina D reduzcan la gravedad de COVID-19, podrían hacerlo, especialmente en personas que tengan niveles bajos. Debido a que generalmente el costo de los análisis de sangre es mayor que el costo de los suplementos (y no es apropiado mientras nuestro sistema de salud está siendo sobre utilizado), y debido a que hay otros beneficios de mantener adecuados niveles de vitamina D, es razonable que la mayoría de las personas considere tomar suplementos de vitamina D.
  • • Muchos de los suplementos multivitamínicos/multi-minerales que están comúnmente disponibles contienen 1000 o 2000 UI de vitamina D, lo cual es un buen objetivo.
    • Personas con piel más oscura (que tienden a tener niveles más bajos debido a que la melanina de su piel bloquea la luz ultravioleta) pueden necesitar más vitamina D; hasta 4000 UI diarias se considera seguro.
  Vitamina D en suplementos de multivitaminas/multiminerales comúnmente disponibles

  MARCA*	Vitamina D (UI)
  ALIVE! ADULT GUMMIES	1200
  CENTRAL-VITE SENIOR (RITE AID)	1000
  CENTRUM ADVANCED FORMULA (LEDERLE)	1000
  CENTRUM CHEWABLES (LEDERLE)	400
  CENTRUM SILVER (LEDERLE)	1000
  CENTRUM SILVER MEN 50+ (LEDERLE)	1000
  CENTRUM SILVER WOMEN 50+ (LEDERLE)	1000
  DAILY MULTIPLE TABLETS FOR MEN (CVS)	700
  DAILY MULTIPLE TABLETS FOR MEN 50+ (CVS)	400
  DAILY MULTIPLE TABLETS FOR WOMEN (CVS)	1000
  DAILY MULTIPLE TABLETS FOR WOMEN 50+ (CVS)	1000
  EQUATE COMPLETE MULTIVITAMIN ADULTS 50+	1000
  EQUATE MEN’S ONE DAILY	700
  EQUATE WOMEN’S ONE DAILY	1000
  MEGA MEN (GNC)	800
  MULTI FOR HER TABLET (NATURE MADE)	1000
  MULTI FOR HIM 50+ NO IRON (NATURE MADE)	1000
  ONE A DAY MEN’S	700
  ONE A DAY MEN’S 50+	700
  ONE A DAY VITACRAVES ADULT MULTI GUMMIES	800
  ONE A DAY VITACRAVES MEN’S MULTIGUMMIES	400
  ONE A DAY VITACRAVES WOMEN’S MULTIGUMMIES	800
  ONE A DAY WOMEN’S	1000
  ONE A DAY WOMEN’S 50+	1000
  PRENATAL Multi + DHA SOFTGELS (NATURE MADE)	1000
  SIGNATURE ADULT GUMMIES (KIRKLAND)	800
  SIGNATURE-DAILY MULTI-VITAMIN/MINERAL (KIRKLAND)	800
  SPECTRAVITE SENIOR (CVS)	1000
  ULTRA MEGA FOR WOMEN (GNC)	1200
  WOMEN’S ULTRA MEGA 50 PLUS  (GNC)	1200

  *La inclusión de marcas de suplementos en esta lista es para referencia y no constituye un endoso. El “Nutrition Source” no endosa ninguna marca en específico.

  • Si no hay suplementos de vitamina D disponibles, una opción es aprovechar un poco de la luz solar, que ahora está empezando a ser suficientemente intensa como para producir vitamina D. Exponga la mayor cantidad de piel posible durante el mediodía y comience con periodos cortos, teniendo mucho cuidado de evitar quemaduras. Quince minutos pueden producir una gran cantidad de vitamina D en piel clara; periodos 3 ó 4 veces más largos puede que se necesiten para piel oscura. Tenga en cuenta que esto es una guía a corto plazo debido a la disponibilidad limitada de suplementos de vitamina D durante la pandemia actual; y no es aconsejable a largo plazo. Dado que la exposición al sol puede contribuir al cáncer de piel, en general es importante evitar la exposición excesiva al sol o el uso de camas de bronceado.
• En este momento, suplementos con mega dosis (mucha más cantidad que la recomendación diaria o RDA) no parecen estar justificados, y pueden resultar dañinos ocasionalmente.
• Evite cualquier suplemento que promueva declaraciones de salud exageradas. En este momento, la Administración de Alimentos y Medicamentos de Estados Unidos (FDA, por sus siglas en inglés) ha estado monitoreando y advirtiendo a las compañías que ofrecen productos fraudulentos que pretenden prevenir, diagnosticar, tratar o curar COVID-19.
• Los suplementos nutricionales no deben considerarse sustitutos de una dieta adecuada, debido a que ningún suplemento contiene todos los beneficios que brindan los alimentos saludables.

Asistencia de traducción provista por Andrea López-Cepero, PhD, Ana Maafs, MEd, y Josiemer Mattei, PhD, MPH (Translation assistance provided by Andrea López-Cepero, PhD, Ana Maafs, MEd, and Josiemer Mattei, PhD, MPH).

Can you briefly summarize the relationship between nutrition and immunity? 

We have known for a long time that nutrition is intricately linked to immunity and to the risk and severity of infections. Poorly nourished individuals are at a greater risk of various bacterial, viral, and other infections. Conversely, chronic or severe infections lead to nutritional disorders or worsen the nutritional status of affected people. Therefore, it is imperative for all of us to pay attention to our diet and nutritional status during the ongoing COVID-19 pandemic. Furthermore, the clinical course of COVID-19 disease tends to be more severe among older individuals and among people with chronic conditions, such as diabetes, hypertension and cancer that are partly related to nutrition. [1] Although data are not yet available, co-infections, such as HIV/AIDS, may also be associated with more severe outcomes, and optimal nutrition plays an important role in maintaining health among people with such infections.

Indeed, consuming good quality diets is always desirable, and this is particularly important during the COVID-19 pandemic. A healthy diet, as depicted by the Healthy Eating Plate, emphasizes fruits, vegetables, whole grains, legumes, and nuts, moderate consumption of fish, dairy foods, and poultry, and limited intake of red and processed meat, refined carbohydrates, and sugar. Added fats should be primarily liquid oils such as olive, canola, or soybean oil.  Such a diet will provide appropriate amounts of healthy macronutrients and essential minerals and vitamins. Eating high-quality sources of protein, fat, and carbohydrate can help maintain a healthy weight and good metabolic state; this is not a time for highly restrictive, crash diets. If someone does develop a COVID-19 infection, eating enough of these healthy calories to prevent unintended weight loss is important. Adequate amounts of minerals and vitamins provided by a healthy diet helps to ensure sufficient numbers of immune cells and antibodies, which are important as the body mounts a response to infections.

Although we have no data regarding nutritional factors in relation to risk and severity of COVID-19, what are some examples of existing evidence on nutrition and infection that would be important to consider?

There have been many studies evaluating intakes of specific nutrients in relation to other infections. To give a few examples:

• Zinc is a component of many enzymes and transcription factors in cells all over the body, and inadequate zinc levels limit the individual’s ability to mount an adequate immune response to infections. [2] Multiple meta-analyses and pooled analyses of randomized controlled trials (RCTs) have shown that oral zinc supplementation reduces the incidence rate of acute respiratory infections by 35%, shortens the duration of flu-like symptoms by approximately 2 days, and improves the rate of recovery. [3,4] The studies were conducted in the US as well as in multiple low- and middle-income countries such as India, South Africa, and Peru. The dose of zinc in these studies ranged from 20 mg/week to 92 mg/day. Dose does not appear to be the main driver of the effectiveness of zinc supplementation.
• Vitamin C is a cofactor for many enzymes. It enhances the function of many enzymes all over the body by keeping their metal ions in the reduced form. It also acts as an antioxidant, limiting inflammation and tissue damage associated with immune responses. [5] RCTs evaluating the effectiveness of vitamin C have been conducted among soldiers, young boys, and older people in the US, the Soviet Union, the UK, and Japan. In these studies, vitamin C supplementation was shown to significantly reduce the incidence of respiratory tract infections. [6] The effectiveness of vitamin C has also been studied among hospitalized patients in the US, Egypt, and Iran, admitted for a wide variety of conditions including severe sepsis, postoperative complications, burns, lung contusions, and cardiac conditions. [7] Vitamin C was shown to reduce the duration of stay in the intensive care unit and need for mechanical ventilation among these patients. [8] The dose of vitamin C varied from 1-3 g/day, and dose does not appear to be the main driver of effectiveness. Doses of vitamin C above 2 g/day should be avoided outside of medical care.
• Evidence from several clinical trials and pooled studies show that vitamin D supplementation lowers the odds of developing acute respiratory tract infections (most of which are assumed to be due to viruses) by 12% to 75%. [9-12] These studies included both the seasonal and pandemic flu caused by H1N1 virus in 2009. The beneficial effect of supplementation was seen in patients across all ages, and individuals with pre-existing chronic illnesses. [13] Among those who were infected, flu symptoms were fewer and recovery was earlier if they had received doses of vitamin D greater than 1000 IU. [14] The benefits were relatively greater in individuals with vitamin D deficiency than in those who had adequate levels of vitamin D.
• Older adults are most often deficient in these helpful micronutrients, and thus can derive the greatest benefit from supplementation. [15,16]

You mention that optimal nutrition plays an important role in maintaining health among people with infections such as HIV/AIDS. Can you expand on that a bit more?

Many acute respiratory tract infections tend to be more severe in people living with HIV/AIDS and other immune deficiencies, [17] and surveillance efforts for COVID-19 targeting these populations are important. Nutrition also has an important role in this category of people. First, HIV infection and malnutrition tend to co-exist. As the disease becomes severe, many people living with HIV tend to be undernourished. Some HIV drugs also lead to metabolic disease. Second, among patients with HIV infection, poor nutritional status and micronutrient deficiencies worsen HIV disease and increase the risk of treatment failure and death. Before the advent of antiretroviral therapy, studies demonstrated that people living with HIV with higher quality diets and better nutritional status tended to live longer and had fewer complications. They were less likely to be anemic and had higher CD4 cell  counts (counts of white blood cells that fight infection). Randomized controlled trials and large cohort studies in Africa and Asia have also shown that the use of multivitamins leads to fewer deaths and slows down disease progression considerably. [18-20] The findings from these studies were consistent whether the HIV-infected patients were receiving antiretroviral therapy or not. In the US, optimal intake of vitamins and minerals was similarly associated with reduced HIV disease progression and mortality. [21] Therefore, good quality diet and multivitamin supplementation are likely to be helpful in reducing the risk of COVID-19 infection among people with HIV and similar diseases.

Is there a role for nutritional supplements in the COVID-19 Pandemic?

Dietary surveys in the US and elsewhere show that most people are consuming diets that do not meet national guidelines—often because of availability or cost—and such diets may not provide optimal quantities of essential vitamins and minerals. Currently, the ongoing COVID-19 pandemic is likely to put many more individuals at risk of food insecurity and make consuming a healthy diet even more difficult. This becomes increasingly likely if the infection risk-mitigation strategies do not include approaches to ensure essential supplies are effectively distributed and accessible, or if the pandemic affects productivity of the agricultural sector.

Although we are not aware of good data on the effects of nutritional supplements on risk or severity of COVID-19, existing evidence indicates that supplements of several nutrients can reduce risk or severity of some viral infections, particularly among people with inadequate dietary sources. Therefore, prudence suggests that inadequate intakes of essential minerals and vitamins be avoided at this time, and supplements can help fill some gaps. Some key points:

• Taking a standard (RDA) multivitamin/multimineral supplement as a nutritional safety net is reasonable. These supplements are a relatively inexpensive (should cost less than $40 USD for a six month supply) and convenient way to replenish and maintain micronutrient stores.
• Maintaining adequate levels of vitamin D is particularly important. Vitamin D is normally produced in our skin when exposed to sunlight, and in the late winter and spring blood levels of vitamin D tend to be low because of reduced sun exposure. Staying indoors will further reduce blood levels. Although we do not have evidence at this time whether vitamin D supplements will reduce the severity of COVID-19, they might, especially among people with low levels.  Because the cost of blood testing is usually more than the cost of supplements (and not appropriate while our health care system is seriously stressed), and because there are other benefits from maintaining adequate vitamin D, taking supplemental vitamin D would be reasonable for most people to consider.
  • Many of the commonly available multivitamin/multimineral supplements do contain 1000 or 2000 IU of vitamin D, which is a good target.
    • People with darker skin (who tend to have lower blood levels because melanin in the skin blocks ultraviolet light) may need more vitamin D; up to 4000 IU per day is considered safe.

• • • If vitamin D supplements are not available, a backup option is to take advantage of some sunlight, which is now starting to become intense enough to produce vitamin D. Expose as much skin as possible in the middle of the day and begin for short periods, being very careful to avoid burns. 15 minutes can produce a large amount of vitamin D in light skin; 3 or 4 times longer will likely be needed for dark skin. Note that this is short-term guidance related to limited vitamin D supplement availability during the current pandemic; and not advisable long-term. Because sun exposure can contribute to skin cancers, in general it is important to avoid excessive sun exposure or use of tanning beds.
• At this time, megadose supplements (many times the recommended dietary allowance, or RDA) do not appear justified, and these can sometimes be harmful.
• Avoid any supplements promoting wild health claims. At this time, the US Food and Drug Administration has been monitoring and warning companies offering fraudulent products claiming to prevent, diagnose, treat, or cure COVID-19.
• Nutritional supplements should be not be considered to be substitutes for a good diet, because no supplements contain all the benefits provided by healthy foods.

Related

Nutrition and Immunity 

Food safety, nutrition, and wellness during COVID-19

However, a new generation of plant-based meat alternatives is aiming to do just that. In a recent JAMA Viewpoint, Dr. Frank Hu, Chair of the Department of Nutrition, and co-authors including Gina McCarthy, Director of C-CHANGE at the Harvard Chan School of Public Health, discuss how popular products like Impossible Foods’ and Beyond Meat’s burger patties are aimed to appeal to a broader consumer base with their “unique mimicry” of beef in both taste and experience. [1] They also note how these products are often marketed as a way to “help reduce reliance on industrial meat production,” aligned with recent reports calling for dietary patterns higher in plant-based foods for both human and planetary health. [2,3]

Can these novel products be considered part of a healthy and sustainable diet? According to the Viewpoint authors, the answer to this question “remains far from clear given the lack of rigorously designed, independently funded studies.” We spoke with Dr. Hu to learn more about the potential benefits and concerns surrounding popular plant-based meat alternatives.

Although these alternative meats are being made from plants, you suggest caution in applying existing research findings on plant-based foods and human health. Can you talk about some of that evidence, and why it’s not readily applicable?

First of all, research has found that diets high in red meat, especially processed meat, have been associated with a range of health consequences, including obesity, type 2 diabetes, cardiovascular disease, and some cancers. At the same time, long-term epidemiologic studies have shown that replacing red meat with nuts, legumes (e.g. lentils, peas, soy, beans), and other plant-based protein foods is associated with lower risks of these chronic diseases and total mortality. [4] Randomized clinical trials have also demonstrated that this replacement reduces levels of total and LDL cholesterol. [5]

However, rather than incorporating plant foods like legumes, these products are generally relying on purified plant protein. They are also highly processed. Food processing may not only lead to the loss of some nutrients and phytochemicals naturally present in minimally processed plant foods; it can also create highly-palatable products. Although short-term, a recent controlled feeding study found that diets high in ultra-processed food cause excess caloric intake and weight gain. [6]  Therefore, we can’t directly extrapolate existing findings on plant-based foods and dietary patterns to these novel products.

Let’s focus on the two products currently dominating the landscape of alternative meats. Given that they’re often being consumed in the form of a burger, what specific questions are raised from a human health perspective?  

Although Beyond Meat and Impossible burger patties contain zero cholesterol, are lower in total and saturated fat than a beef burger patty, and similar in protein and calories as a beef burger patty, they are both higher in sodium. As we note in the Viewpoint, there is no existing evidence to substantiate whether these nutrient differences alone offer any significant health benefit as a replacement.

People also aren’t typically eating burger patties on their own, so we also have to think about the broader context in which they’re consumed. For example, when placed between a bun made of refined grains, covered in sauces and other toppings, and accompanied by French fries and soda, we can’t assume that substituting one of these alternative patties for a burger patty will improve overall dietary quality.

These products achieve their imitation of meat through different processing technologies. Can you briefly explain how they differ, and if there are any unique concerns related to the methods used?

In a beef burger, the inherently “meaty” flavor is derived from an iron-containing molecule called heme. Impossible Foods actually takes heme from the roots of soy plants and ferments it in genetically engineered yeast. The high amounts of heme that end up in the burger give a meaty flavor and appearance. One potential concern that has been raised is that higher intake of heme iron has been associated with increased body iron stores and elevated risk of developing type 2 diabetes. [7]

Beyond Meat does not use heme, but rather a processing method that (according to information from the company) “aligns plant-proteins in the same fibrous structures you’d find in animal proteins,” and then combines fats and minerals that mimics the composition and flavors of meat. Pomegranate powder and beet juice impart a “bloody” red color.

What do you propose as a way forward in researching these novel meat alternatives?

Since these are so new and rapidly developing, it won’t be feasible to conduct large, long-term trials on disease outcomes. However, short-term, independently-funded intervention trials can be conducted to compare the effects of these products—both with their animal-based counterparts as well as minimally-processed plant protein sources—on cardiometabolic risk factors and other factors including the microbiome. Intervention and observational studies can also examine how these plant-based meat alternatives influence overall diet quality, caloric intake, nutrient status, and body weight. Zooming-out, we’ll also need to look at whether an increase in these alternatives actually leads to reduced red meat intake.

Of course, any research on this topic will not be without its challenges. With technological innovations and product reformulations, the products on the market may change quickly in both composition and availability. Red meat replacements are most popular now, but others being introduced or developed may include fish and poultry. Beyond plant-based meats, another product suite on the horizon is lab-grown meats, where animal cells are cultured to provide the product without raising and slaughtering the animal.

What are some other implications of these technologies that should be considered in researching and discussing this topic?

The goal of these technologies is to disrupt the status quo of conventional animal agriculture, which can have important public health, regulatory, and environmental implications. Regarding our planet’s health, these technologies could represent a significant opportunity to reduce greenhouse gases that fuel climate change, as well as other concerns related to existing industrial animal-based food production. For example, a Beyond Meat-commissioned Life Cycle Assessment found that the Beyond Burger generates 90% less greenhouse gas emissions, requires 46% less energy, 99% less water, and 93% less land use than a burger made from U.S. beef. [8] To be clear, such findings warrant further independently-funded studies. We should also remember to consider these products as compared with the production of minimally processed plant-based foods.

When examining these shiny new technologies, what are some key points we should not lose sight of?

As the global demand for meat is projected to increase in coming decades, these technologies may have a role to play. However, they are far from the only answer to calls for shifting to more plant-based dietary patterns. Enthusiasm around plant-based meats and other alternatives should not distract from the bigger picture that a healthy dietary pattern includes an abundant amount of minimally processed plant foods—vegetables, fruits, whole grains, legumes, and nuts; moderate amounts of dairy products, seafood, and poultry; and lower amounts of processed and red meat, sugar-sweetened foods and beverages, and refined grains.

Paraphrasing our Viewpoint conclusion, a fundamental change in the food system requires policies and actions that create a culture in which healthy and sustainable food choices are accessible, affordable, enjoyable, and the norm. Technology will certainly play a role, but we need to keep an eye on new innovations to ensure they are beneficial to both human and planetary health, and consider any unintended consequences.

We talked to lead author Dong Wang, a research fellow in the Department Nutrition, to take a closer look at the study.

1. Existing research has shown distinct associations between dietary fat and cardiovascular disease, however this study goes well beyond just one outcome. Tell us a bit more about the study design and what you set out to investigate.

Our objective was to examine the associations of specific dietary fats with both total and cause-specific mortality. We investigated 126,233 participants from two prospective cohort studies, the Nurses’ Health Study and Health Professionals Follow-Up Study. These men and women were free from cardiovascular disease, cancer, and diabetes at baseline when they joined the cohort, and dietary fat intake was assessed initially and updated every two to four years using validated food frequency questionnaires. Because of this very large sample size, combined with repeated and validated measurements of diet and lifestyle over an extended period of follow-up (up to 32 years), this study is by far the most detailed and powerful examination of this topic.

2. The study concludes that different types of dietary fat have “divergent effects on mortality.” What are the key findings on trans, saturated, and unsaturated fats?

Our study found that higher intake of saturated fat (found in foods like butter, lard, and red meat) and especially trans fat (predominantly from partially hydrogenated vegetable oil), was associated with greater risk of mortality when compared with the same number of calories from carbohydrate. When compared with carbohydrates, every 5% increase of total calories from saturated fat was associated with an 8% higher risk of overall mortality, and every 2% higher intake of trans fat was associated with a 16% higher risk of overall mortality.

Alternatively, higher intake of unsaturated fats compared to carbohydrates—including both polyunsaturated fats and monounsaturated fats from primarily plant-based foods—was associated with between 11% and 19% lower overall mortality for an increase in 5% of total calories. Polyunsaturated fats, which include both omega-6 fatty acids (found in most plant oils, nuts, and seeds), and omega-3 fatty acids (found in high concentrations in walnuts, flax seeds, soybean oil, and fish), were associated with lower risk of premature death.

3. Overall, these findings are consistent with the dietary recommendations to eliminate trans fat and to replace foods high in saturated fat with sources of unsaturated fat. Why is this particular replacement so beneficial?

Indeed, trans fats had the most significant negative impact on health. Fortunately, trans fats are less and less accessible due to the recent reductions of partially hydrogenated oils from our processed food supply.

When it comes to saturated fat, what you replace it with matters. People who replaced saturated fat in their diets with unsaturated fats—especially polyunsaturated fats—had a far lower risk of death from any cause, as well as death due to cardiovascular disease, cancer, neurodegenerative disease, and respiratory disease. Those who replaced saturated fat with carbohydrates only slightly lowered mortality risk. This is most likely because carbohydrates in typical American diets are high in refined starch and sugar, which have a similar influence on mortality risk as saturated fats.

4. The finding for cardiovascular disease is also consistent with existing guidelines based on evidence of reduced total and LDL cholesterol when unsaturated fats replace trans or saturated fats. Yet debate persists surrounding the health benefits of limiting saturated fat or butter. From where does this controversy stem, and how does your research help clear-up the confusion?

The recent widespread confusion about the health effects of specific types of dietary fat is in part caused by a misleading 2014 Annals of Internal Medicine paper, which concluded there is no evidence supporting the longstanding recommendation to limit saturated fat consumption and replace it with unsaturated fats. The authors of this paper employed a meta-analysis (a statistical analysis that summarizes data from many different studies), and therefore could not look at specific macronutrient comparisons with saturated fat. In addition, this paper also had errors in data extraction, omitted important studies, and only examined coronary heart disease.

In addition, a recently published BMJ paper based on 1960’s data from the Minnesota Coronary Experiment suggested that replacing saturated fat with vegetable oils rich in linoleic acid was not protective against death from coronary heart disease or all causes, which appeared to challenge current guidelines and added further confusion. However, this study was of very short duration, extremely low in follow-up rate, and the intervention likely reduced intake of important omega-3 polyunsaturated fatty acids. The extreme intervention diet was also never consumed by any appreciable number of Americans and likely confounded by intake of trans fat.

Finally, a new systematic review and meta-analysis looking at the association of butter consumption (a concentrated source of saturated fat) with chronic disease and all-cause mortality resulted in headlines touting “butter is back,” even though the findings were predominantly neutral, and the authors pointed out that unsaturated fats were found to be a better choice than butter.

Our research provides a much more comprehensive examination because we were able to look at specific comparisons between different types of fat or carbohydrate. We also examined a much broader range of outcomes, including total mortality and mortality due to cardiovascular disease, cancer, neurodegenerative disease and respiratory disease. To our knowledge, this is by far the most detailed and powerful examination of these important issues, and is supportive of the strong evidence base of current dietary recommendations that emphasize limiting saturated fat, eliminating trans fat, and replacing these with plant-based oils and other foods high in unsaturated fat.

5. So in terms of disease-specific mortality in relation to dietary fat intake, what correlations did you find?

• Higher trans fat intake was associated with significantly higher risk of neurodegenerative and respiratory disease mortality.
• Higher saturated fat intake was associated with a substantial increase in mortality due to respiratory disease.
• Higher intakes of monounsaturated and polyunsaturated fats were associated with lower risk of neurodegenerative and respiratory disease mortality.
  • Intake of omega-3 polyunsaturated fatty acids, primarily alpha-linolenic acid (found in vegetable oils and nuts—especially walnuts—flax seeds, flaxseed oil, and leafy vegetables), was associated with lower risk of death due to neurodegenerative disease.
  • Intake of marine-based omega-3 polyunsaturated fatty acids (mainly from fish) was associated with lower respiratory disease mortality and sudden cardiac death.
  • Intake of omega-6 polyunsaturated fatty acids (found in vegetable oils, nuts, and seeds) was associated with lower risk of total death and death due to cardiovascular disease, cancer, and respiratory disease.

6. Based on this study, what are some simple steps consumers can take to improve their diet?

Overall, when it comes to dietary fat, what matters most is the type of fat you eat. This study documents the important benefits of unsaturated fats, especially when they replace saturated and trans fats. In practice this can be cutting back on red meat to incorporate more fish, nuts, and seeds, and replacing butter when cooking with a variety of liquid vegetable oils, such as olive, canola, and sunflower oil.  It’s also important to limit refined grains, potatoes, and added sugar.

Read the press release about the study from HSPH News

More information on the different types of dietary fat

Existing research on dietary fat and disease

Our expert examines a recent paper (1) based on 1960’s data that challenges current guidelines on the benefits of replacing saturated fat with polyunsaturated fat.

In the 1968, the Minnesota Coronary Experiment (MCE) set out to test the traditional “diet-heart” hypothesis, which predicts that replacing saturated fat with vegetable oils rich in linoleic acid (the primary n-6 polyunsaturated fatty acid in our diet) reduces coronary heart disease (heart attacks) by lowering serum cholesterol. Though the initial results of the trial reported no reduction in mortality as a result of a linoleic-acid enriched diet (2), the experiment had serious limitations, largely beyond the control of the investigators.

50 years later, we have a much better picture of the many pathways that connect diet with heart disease, including the importance of including n-3 polyunsaturated fatty acids  (absent from the MCE intervention diet) along with n-6 polyunsaturated fatty acids. Current dietary recommendations that emphasize replacing saturated fat with polyunsaturated fat (including both n-3 and n-6) are backed by multiple lines of evidence, and the 60 percent decline in coronary heart disease mortality in the US since the 1960’s underlines the importance of this guidance (3).

However a recent paper (1) is attempting to challenge current guidance by re-examining MCE data, claiming an “overestimation of the benefits of replacing saturated fat with vegetable oils rich in linoleic acid.” We sat down with Nutrition Department Chair Dr. Walter Willett, to help clear up this new controversy surrounding dietary fat, taking a closer look at the study design of the original MCE trial, what actually happened in conducting the trial, and how the 1960’s data stack up to today’s research.

Does this trial conducted over 50 years ago have any relevance to our current guidelines on dietary fat? How does this reevaluation of data fit in with newer findings about the connection between diet and heart disease?

This is an interesting historical footnote that has no relevance to current dietary recommendations.  We have known for many years that the classical diet-heart hypothesis is incomplete, including that we have recognized the importance of including n-3 fatty acids as well as n-6 fatty acids, the roles of different cholesterol fractions, and the many other pathways that connect diet with heart disease.

The MCE’s intervention diet replaced saturated fat with linoleic acid from corn oil. How was that accomplished and how does this swap align with current or past recommendations?  

The diet used in the MCE was never consumed by any appreciable number of Americans and the level of linoleic acid was well above the range recommended by the American Heart Association or any other group. To reach these levels, investigators created fake meat, cheese, and milk by removing as much of other types of fat as possible, replacing these with corn oil.  Whatever small amounts of n-3 fatty acids were present would have been largely removed.  It’s also important to note that investigators  created a special corn oil margarine that was lower in trans fat than the standard margarine, but we now know that the most dangerous types of trans fat (18:2 trans isomers) are likely to be higher in these lightly hydrogenated products than in the more heavily hydrogenated forms (4).

Randomized controlled trials, used in the MCE, are often referred to the “gold standard” when it comes to studying dietary intervention and disease. How important a role does study duration play when looking at the long term of effects of diet on risk of heart disease? How did the MCE’s study design stack up?

The most serious problem with the MCE is the very short duration, as this trial was the victim of the deinstitutionalization of mental health hospitals that occurred in the 60’s and 70’s. The original authors had determined that nearly 10,000 participants needed to be followed for at least three years to detect a likely benefit, and enrolled 9423 women and men aged 20 to 97. Researchers identified patients hospitalized with mental illness as a good population to study because they were a “captive audience” who would be available for investigation over many years.  However, largely because of patients being discharged, they lost nearly 75 percent of their participants within the first year.  From this report, it seems that only about half of the remaining patients stayed a full three years, which is still a short time to study the effects of diet on atherosclerosis.  The study was clearly a failure for reasons beyond the control of the investigators, and it adds very minimal information, if any, about the long-term effects of diet on risk of heart disease.

In this recent BMJ paper, Ramsden et al. recovered previously unpublished data from the MCE to put its findings in context with existing diet-heart trials through systematic review and meta-analysis. What does this reevaluation add to the MCE’s original conclusions?

The main results of the MCE were published by Frantz et al. (2) in 1989 with all of the aforementioned limitations, and no differences were reported between the treatment and control groups for cardiovascular events, cardiovascular deaths, or total mortality.  The report of “recovered” data by Ramsden et al. (1) in BMJ adds no new data regarding these conclusions. The causes of death in the BMJ paper are not known, which makes evaluation of total mortality in non-randomized analysis relating degree of cholesterol reduction to death particularly uninformative. A small amount of new but incomplete data on autopsies were included, however the average follow up to autopsy was less than one year from baseline, making it unlikely that any benefit on gross autopsy findings for atherosclerosis would be seen.

Ramsden et al. include a meta-analysis of previously published data examining mortality from coronary heart disease. In addition to major limitations of the MCE and other diet-heart studies included in the meta-analysis, the statistical power was low for cardiovascular mortality and the confidence interval includes a potentially important benefit. Very importantly, the authors failed to mention that they earlier reported a benefit for incidence of coronary heart disease in a meta-analysis of randomized trials in which saturated fat was replaced by vegetable oils high in linoleic acid with a small amount of n-3 polyunsaturated fatty acids, usually as soybean oil (5). This finding is consistent with other summaries of published evidence and current dietary recommendations for replacing saturated fat with oils high in polyunsaturated fats.  Notably, n-3 fatty acids can be obtained from seafood as well as plant oils, but seafood intake was likely to be low in Minnesota during the time when the MCE was conducted.

What would you say to those doubting the established guidelines surrounding the health benefits of replacing saturated fat with polyunsaturated fats as a result of this report? With this in mind, where should the research on dietary fats go next?

The bottom line is that this report adds no useful new information and is irrelevant to current dietary recommendations that emphasize replacing saturated fat with polyunsaturated fat, including sources of both n-3 and n-6 fatty acids. Many lines of evidence support this conclusion, including beneficial effects on blood lipids (6), summaries of prospective cohort studies (7), and randomized trials (8)—including the meta-analysis previously published by the authors in Ramsden et al. (5). Notably, since the 1960’s, the US diet has changed in this way; intake of linoleic acid has approximately doubled, and this has corresponded to a greater than 60 percent decline in coronary heart disease mortality (3). Although multiple factors have contributed to this decline, none of the other factors can explain this huge improvement in health, and the replacement of saturated fat with polyunsaturated fat (both n-6 and n-3 fatty acids) is almost certainly a major, probably most important, factor. Reversing these changes would almost certainly result in great harm.

Although we have a high level of evidence that the direction  of current dietary recommendations will be beneficial, more research is desirable to determine optimal intakes of different types and sources of dietary fat and their effects on various health outcomes.

References

1. Ramsden CE, Zamaora D, Majchrzak-Hong S, et al. Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73). BMJ, 2016;352:i1246.
2. Frantz ID Jr., Dawson EA, Ashman PL, et al. Test of effect of lipid lowering by diet on cardiovascular risk. The Minnesota Coronary Survey. Arteriosclerosis, 1989;9:129-35.
3. Willett, W. (2013). Nutritional epidemiology, Third Edition. Oxford: Oxford University Press.
4. Sun Q, Ma J, Campos H, et al. A prospective study of trans fatty acids in erythrocytes and risk of coronary heart disease. Circulation 2007 Apr 10;115(14):1858-65.
5. Ramsden CE, Zamora D, Leelarthaepin B, et al. Use of dietary linoleic acid for secondary prevention of coronary heart disease and death: evaluation of recovered data from the Sydney Diet Heart Study and updated meta-analysis. BMJ, 2013;346:e8707.
6. Mensink, R.P., et al., Effects of dietary fatty acids and carbohydrates on the ratio of serum total to HDL cholesterol and on serum lipids and apolipoproteins: a meta-analysis of 60 controlled trials. Am J Clin Nutr, 2003. 77(5): p. 1146-55.
7. Farvid MS, Ding M, Pan A, et al. Dietary linoleic acid and risk of coronary heart disease: a systematic review and meta-analysis of prospective cohort studies. Circulation, 2014;130:1568-78.
8. Dietary Guidelines Advisory Committee. Report of the Dietary Guidelines Advisory Committee on the Dietary Guidelines for Americans, 2015, to the Secretary of Agriculture and the Secretary of Health and Human Services: U.S. Department of Agriculture, Agricultural Research Service, Washington D.C.; 2015. Available from: http://health.gov/dietaryguidelines/2015-scientific-report/

Dr. David Ludwig, MD, PhD, a professor in the Department of Nutrition at Harvard T.H. Chan School of Public Health, and director of the New Balance Foundation Obesity Prevention Center at Boston Children’s Hospital, is one of the foremost experts when it comes to carbohydrates. His research focuses on the effects of diet on hormones, metabolism and body weight, and he developed a “low glycemic load” diet – one that decreases the surge in blood sugar after meals – for the treatment of obesity-related diseases.

• In a 2013 editorial (1), he and Dr. Walter Willett explain that “Many starchy foods, particularly highly processed grains and potato products, have a high glycemic index, raising blood glucose and insulin more rapidly than an equivalent amount of sucrose” – going on to explain that refined grain and potato products have metabolic effects comparable to those of sugar.
• In a JAMA viewpoint article (2), Dr. Ludwig examined the health effects of fructose, explaining that “Excessive intake of refined sugar plays a significant role in the epidemics of obesity and related diseases.” He also noted that rapidly absorbed forms of glucose—present in both sugar and high glycemic index starch—also contribute to these diseases.

Here, we ask Dr. Ludwig to help clear up the carbohydrate confusion.

Sugar has been singled out as one of the worst dietary offenders. However, you make the case that highly processed carbohydrates and potato products are just as bad. Should there be more public health campaigns focused on carbohydrate quality as opposed to sugar-sweetened beverages, which most people already know are unhealthy?

With trans-fat now leaving the food supply, highly processed carbohydrate now comprises the most unhealthful component of the food supply. Added sugar has received lots of attention recently – and for good reason. However, Americans consume more calories from refined grains and potatoes than from sugar. Starchy foods like white bread, white rice, potato products, crackers and cookies digest quickly into glucose, raise insulin levels, program the body for excessive weight gain and increase risk for chronic disease.

Indeed, an exclusive focus on sugar could miss the mark in two ways:

1) By discouraging consumption of whole fruits, the natural delivery vehicle for sugar. Whole fruits have numerous health benefits, and virtually no side effects for most people because the sugar is digested and absorbed from whole foods slowly.

2) By leading to an increase in refined grain intake. For example, highly processed rice cereal and table sugar may taste different, but below the neck they both cause metabolic problems.

The distinction between sugar and starch is largely meaningless from a biological perspective. The key public health challenge today is to reduce intake of all highly processed carbohydrates in favor of whole carbohydrates (fruits, vegetables, legumes and minimally processed grains) and healthful fats (like nuts, avocado and olive oil).

Much of your research focuses on the glycemic index. In a 2015 article you wrote that reports of its demise have been exaggerated (3). Is the glycemic index still a useful tool for the average consumer, and if so, how can people incorporate it into their lives in a practical way?

The glycemic index (GI) is a scientific term that describes how controlled amounts of carbohydrate affect blood glucose (and by implication, insulin levels) after consumption.

When first proposed in 1981, the GI was a radical notion because it implicitly suggested that all carbohydrates aren’t alike, contrary to conventional opinion. Since then hundreds of clinical trials, observational studies and mechanistic investigations have laid a solid foundation for understanding why a high GI diet could harm health. Of course, like any area in nutritional research, not every study comes to exactly the same conclusions – in part because of the inherent complexities of diet and the difficulties of conducting high quality long-term trials. Also, some experts have criticized GI because a few ostensibly unhealthy foods have a low GI (like ice cream or the sugar fructose). However, no single dietary component could ever adequately describe a healthful diet. Though protein is indisputably critical to health, we wouldn’t focus entirely on that one nutrient to the exclusion of everything else.

The bottom line is that GI has been extremely useful in the research setting for characterizing carbohydrate quality. But for most people, there’s no need to “eat by the numbers” – either glycemic index, total calories (4) or any other scale. Choosing whole instead of highly processed carbohydrates will naturally result in a low GI diet that will also have many other nutritious aspects including high content of fiber, vitamins, minerals and polyphenols. (Note: Use of GI as a guide to food selection may have specific benefit for people with diabetes or other severe metabolic problems.)

In an editorial published in NEJM, you suggest that diets low in glycemic index and moderately high in protein should be given special consideration, as they may reduce glycemic load and promote weight loss – and also might be less psychologically burdensome because no macronutrient or major food group is entirely omitted (5).

How do carbs figure in to a “low glycemic and moderately high protein” diet – is carbohydrate quality more important than the amount?

The optimal macronutrient ratio – that is, the relative proportions of protein, carbohydrate and fat – has been the subject of intense debate for decades. Despite hundreds of studies on the topic, we still don’t know whether one special combination is best for everyone, or which ratios are best for specific medical conditions. In the absence of definitive data, much can be learned by taking the truly long-term perspective – that humans across the globe have done well on diets with widely ranging macronutrients. The Inuits in the far North traditionally ate mostly fat and protein; whereas some native populations in the tropics consumed mostly carbohydrate.

Ultimately, the choice of how to balance macronutrients is individual, influenced by culture, food availability, and personal preference. So long as adequate attention is directly to food quality, the relative ratios are probably of secondary importance in most situations (again, excepting individuals with metabolic problems like insulin resistance). That said, it becomes increasing difficult to avoid excessive intake of processed carbohydrates as total carbohydrate rises. For that reason, many people will benefit by increasing intake of foods high in fat and protein (including plant-based sources).

Can you talk more about carbohydrate quality – what are some of the best and worst sources, and how can people more easily determine what to eat? For example, many products claim to be whole wheat, but in actuality may still be highly refined. Also, is there a daily amount of carbohydrate – in grams, or in serving sizes – that people should aim for?

A primary focus on the nutritional factors on a label has at times backfired, leading to the creation of industrial food products that might satisfying guidelines but undermine health. Heavily milled “whole grain” flour may have the same fiber content as natural whole kernel grains, but they digest much faster, causing more rapid swings in blood glucose and higher insulin levels. Especially when eating grains, choose traditional versions our ancestors would have eaten – steel-cut (old-fashion) oatmeal, farro, whole barley and rye, buckwheat and quinoa. In addition, a wide range of unprocessed carbohydrates can contribute to diet quality, including whole fruits (especially non-tropical varieties), non-starchy vegetables, legumes and nuts.

Carbohydrates have been a hot topic in nutrition for decades – two popular “fad” diets were the Atkins diet and the South Beach Diet, both of which limited carbohydrate consumption. Is it possible that these diets actually had some substance behind the hype?

The fastest way to stabilize blood glucose and lower insulin levels is to reduce carbohydrate. The Atkins and South Beach Diets achieved great popularity during the low-fat craze by offering an effective antidote to all the processed carbohydrate in the American diet. For many people, these low carbohydrate diets have produced tangible benefits, for sound scientific reasons.

In recent years, very-low- and no- carb diets have become more popular, and ketogenic diets – which are higher in fat and lower in carbohydrate, forcing the body to use fat as the primary fuel source – are sometimes implemented for therapeutic purposes. Do you see these types of diets as useful in treating disease? Should people consider adopting ketogenic diets as a preventative measure?

For people with type 2 diabetes or related metabolic problems, very low carbohydrate diets including the ketogenic diet may offer an excellent long-term option. In some cases, a very low carbohydrate diet can reverse diabetes rapidly, without severe calorie deprivation. Much more research is needed in this area. But despite their potentially dramatic effects, very low carbohydrate diets can be difficult to maintain over the long-term. Replacing added sugars and refined starchy foods with unprocessed carbohydrate, healthful fats and proteins may provide many of the benefits of a very low carbohydrate diet, without having to eliminate an entire class of nutritious (and delicious) foods.

Dr. Ludwig addresses these ideas further in his forthcoming book Always Hungry? Conquer Cravings, Retrain Your Fat Cells, and Lose Weight Permanently.

References

1) Willett WC, Ludwig DS. (2013) Science souring on sugar. BMJ. 346:e8077.

2) Ludwig DS (2013) Examining the health effects of fructose. JAMA. 310(1):33-4.

3) Ludwig DS, Astrup A, Willett WC (2015) The glycemic index: Reports of its demise have been exaggerated. Obesity (Silver Spring). 23(7):1327-8.

4) Ludwig DS, Friedman MI. (2014) Increasing adiposity: consequence or cause of overeating? JAMA 311(21):22167-8.

5) Ludwig DS, Ebbeling CB. (2010) Weight-loss maintenance–mind over matter? N Engl J Med. 363(22):2159-61.

Legumes, which include beans, peas and lentils, are an inexpensive, healthy source of protein, potassium, and complex carbohydrates, including dietary fiber.

• On average, legumes contain about 20-25% protein by weight on a dry basis, which is 2-3 times more protein than wheat and rice. However, they tend to be low in the essential amino acid methionine, and sometimes tryptophan.
• Legumes are also a very good source of dietary fiber, which is important for maintaining healthy bowel function.
• The content of total carbohydrate, including complex carbohydrates, ranges from 65-72% by weight on a dry basis, of which 85% is composed of starch, while dietary fiber constitutes anywhere from 10-20% of the weight of dried legumes (1).

The high level of both starch and dietary fiber raises a very interesting question. If most of the carbohydrate is made of starch, how can legumes be such good sources of dietary fiber? Isn’t all starch rapidly digested to glucose? This was the prevailing view of starch until the 1980s, when two English researchers, Hans Englyst and John Cummings discovered that not all starch is rapidly digested to glucose in the small intestine (2).

• They found that some starch is resistant to digestion and passes into the large intestine where much of it is used as a food source by the healthy bacteria living in our colon. Englyst and Cummings named this previously unknown form of starch “resistant starch” and concluded it acts similar to dietary fiber.
• Substantial research since their discovery has confirmed that resistant starch (RS) functions much like dietary fiber in food (3).

There are two main forms of dietary fiber in food:

1. One is insoluble fiber comprised of complex carbohydrates, such as cellulose, that are insoluble in the gastrointestinal fluid. This form of fiber is not broken down by gut bacteria, acts as a bulking agent, and is effective at reducing constipation.
2. The other form of fiber is soluble in gastrointestinal fluid, producing a thick, viscous liquid similar to honey. Soluble fiber is readily metabolized by gut bacteria, which convert much of it into small molecules called short-chain fatty acids (SCFA). The cells lining the colon obtain about 60-70% of their energy from SCFA (4).

Although resistant starch does not increase the viscosity of the gastrointestinal fluid, it is one of the best sources of SCFA helping to maintain the health of colonic cells.

• Since resistant starch is not metabolized in the small intestine it reduces the amount of glucose released into the blood, thus lowering the demand for insulin while also reducing the caloric density of food (5).
• Foods that contain significant levels of resistant starch increase satiety and have a lower glycemic index, producing a smaller rise in blood glucose than high starch foods that contain very little resistant starch, such as baked potatoes, rice, and white bread (6). Clearly, not all carbohydrate is alike.

Legumes are one of the best sources of resistant starch. Raw, dried legumes contain about 20-30% resistant starch by weight (7). That means almost half of the starch in raw legumes is resistant to digestion.

Why is some starch resistant to digestion? A small portion of it is physically inaccessible to digestive enzymes. But most of it is resistant due to the chemical structure of starch. Starch is composed of two molecules called amylose and amylopectin.

• Amylose is a linear chain of glucose molecules linked end-to-end.
• Amylopectin is a much larger molecule with numerous branches of short chains of glucose molecules linked to a main chain like the branches of a tree growing from the trunk.

The starch molecules, especially amylose, form crystalline regions that are resistant to digestion by the starch digesting enzymes in our body (3). Compared with other high starch foods like corn, wheat, and rice, the starch in legumes is very high in amylose, comprising up to 40% of the starch, making it more resistant to digestion.

• It is important to realize that resistant starch is not a distinct molecular structure like glucose or cholesterol, but a concept developed to explain why some starch is not digested (8).
• The amount of resistant starch reported in foods is therefore highly dependent on the method used to analyze for resistant starch. In 2000 a standardized test for determining the content of RS in food was approved by AACC International (9). The numbers reported in this article were determined by this method (10).

If cooked legumes contained as much resistant starch as raw legumes we would have a very difficult time digesting them. As with all high starch foods, when legumes are cooked in boiling water large portions of the crystalline regions are destroyed, reducing the amount of resistant starch. But since legumes are so high in amylose, a smaller amount of resistant starch is destroyed by cooking than in other foods because some forms of crystalline amylose are stable even in boiling water (8).

• Fully cooked legumes contain only about 4-5% of their total weight (on a dry basis) as resistant starch, regardless of how long they are cooked.
• Cooling the cooked legumes for up to 24 hours in the refrigerator increases the level of resistant starch to 5-6% of the total weight (dry basis) by allowing some of the starch molecules to recrystallize. Canned whole beans contain about the same amount, as do canned refried beans (10).

This may not seem like much resistant starch, but it is still 4-5 times higher than other starchy foods such as white bread and potatoes (see table below). This is certainly enough to have a significant impact on the formation of SCFA, glycemic index, reduced insulin response, satiety and caloric content (11). In sum, legumes are a healthy choice not only for their high content of protein and other nutrients, but also because they contain some of the highest levels of resistant starch of any food.

• Weight percent on dry basis
  ** A glycemic index below 55 is considered a low G. I. food (12).

 References

1. United States Department of Agriculture National Nutrient Database for Standard Reference (2011).

2. Englyst, H. N., Kingman, S. M., and Cummings, J. H., Classification and Measurement of Nutritionally Important Starch Fractions. Eur. J. Clin. Nutr. 1992; 46: 533-550.

3. Crosby, G. A., Resistant Starch Makes Better Carbs. Functional Foods and Nutraceuticals, 2003; 6: 34-36.

4. Topping, D. L., and Clifton, P. M., Short-Chain Fatty Acids and Human Colonic Function: Roles of Resistant Starch and Non-starch Polysaccharides. Physiol. Rev. 2001; 81(3): 1031-1064.

5. Behall, K. M., and Howe, J. C., Contribution of Fiber and Resistant Starch to Metabolizable Energy. Am. J. Clin. Nutr. 1995; 62: 1158S-1160S.

6. Raban, A., et al. Resistant Starch: The Effect on Postprandial Glycemia, Hormonal Response, and Satiety. Am. J. Clin. Nutr. 1994; 60: 544-551.

7. Bednar, G. E., et al. Starch and Fiber Fractions in Selected Food and Feed Ingredients Affect Their Small Intestinal Digestibility and Fermentability and Their Large Bowel Fermentability in Vitro in a Canine Model. J. Nutr. 2001; 131: 276-286.

8. Thompson, D. B. Strategies for the Manufacture of Resistant Starch. Trends Food Sci. Tech. 2000; 11(7): 245-253.

9. Perea, A., Meda, V., and Tyler, R. T. Resistant Starch: A Review of Analytical Protocols for Determining Resistant Starch Content of Foods. Food Res. Intern. 2010; 43: 1959-1974.

10. Fabbri, A. D. T., Schacht, R. W., and Crosby, G. A. Evaluation of Resistant Starch Content of Cooked Black Beans, Pinto Beans and Chickpeas. NFS Journal 3. 2016; 8-12. 

11. Noah, L. et al. Digestion of Carbohydrate from White Beans (Phaseolus vulgaris L.) in Healthy Humans. J. Nutr. 1998; 128: 977-985.

12. Brand-Miller, J., Wolever, T. M. S., Colagiuri, S., and Foster-Powell, K. The Glucose Revolution: The Authoritative Guide to the Glycemic Index. Marlowe & Co., NY, 1999.

I’m confused about whether canola oil is healthy. I know that it’s a polyunsaturated fat, which I’m told is good, but then I also hear that I should stay away from it.

Some of the claims:

• Most canola is chemically extracted using a solvent called hexane, and heat is often applied which can affect the stability of the oil’s molecules, turn it rancid, destroy the omega-3s in it, and can even create trans fats.
• “Cold-pressed” canola oil exists but is very expensive and hard to find.

Should I avoid canola oil?
And what are the best fats in general for cooking?

The top four vegetable oils consumed in the United States are soybean, canola, palm, and corn oil. These are referred to as refined, bleached, deodorized oils – or RBD for short – because this describes the process by which they are manufactured.

• RBD oils are produced by crushing the plant material, usually seeds, to express the oil, followed by extraction of the crushed material with a low-boiling solvent, most commonly hexane, to obtain the remainder of the oil.
• Canola oil is generally considered a “healthy” oil because it is very low in saturated fat (7%). Like olive oil it is high in monounsaturated fat (63%).
• Canola oil also contains a significant level of polyunsaturated omega-3 (ω-3) fat (9-11%),
• In addition, canola oil contains significant amounts of phytosterols (about 0.9% by weight) that reduce the absorption of cholesterol into the body.

As with many highly processed food products there are concerns about the safety of canola oil.

First is the use of a solvent such as hexane to extract the maximum amount of oil from the seed. Hexane is a very volatile solvent (boiling point 69ºC, or 156ºF) with a very low toxicity (LD₅₀ in rats of 49.0 milliliters per kilogram). Hexane has been used to extract oils from plant material since the 1930s, and “there is no evidence to substantiate any risk or danger to consumer health when foods containing trace residual concentrations of hexane are ingested.” [1]

It has been estimated that refined vegetable oils extracted with hexane contain approximately 0.8 milligrams of residual hexane per kilogram of oil (0.8 ppm). [2] It is also estimated that the level of ingestion of hexane from all food sources is less than 2% of the daily intake from all other sources, primarily gasoline fumes. There appears to be very little reason for concern about the trace levels of hexane in canola oil.

Another concern is the report that canola oil might contain trans-fats that have been linked with significant health problems. In fact, canola oil does contain very low levels of trans-fat, as do all oils that have been deodorized. Deodorization is the final step in refining ALL vegetable oils. This process produces the bland taste that consumers want.

As a comparison, the fat of cattle and sheep, as well as the milk obtained from cows, contain about 2-5% of natural trans-fat as a percent of the total fat. [3] When canola oil is deodorized it is subjected to temperatures above 200ºC (as high as 235ºC, 455°F) under vacuum for various lengths time to remove volatile components such as free fatty acids and phospholipids. During exposure to these high temperatures a small amount of the unsaturated fatty acids, especially the essential ω-6-linoleic and ω-3–linolenic acid, are transformed into trans-fatty acid isomers. Because of earlier studies showing that even quite low levels of trans isomers of ω-3–linolenic can have adverse effects of blood cholesterol fractions, the processes used for deodorization have been modified to limit the production of these compounds.

Other vegetable oils, and even nut oils, have been found to contain levels of  trans-fatty acids that are comparable to the levels in beef fat. The table below summarizes the content of trans-fatty acids found in a number of oils. [4] In both canola oil and soybean oil, trans-isomers of linoleic acid have been found to account for 0.2-1.0% of total fatty acids, while trans-isomers of linolenic acid may total as much as 3%. [5] Linolenic acid isomerizes with heat about 12-15 times faster than linoleic acid.

*Results of multiple samples of commercial oil
** Partially hydrogenated soybean oils for comparison

A consequence of transforming some of the natural unsaturated fatty acids to trans-fat during the deodorization step is a reduction in the content of beneficial ω-3–fatty acids.

• Heating bleached canola oil at 220°C for ten hours reduces the content of linolenic acid by almost 20%. [5] Keep in mind that canola oil sold in the supermarket still contains 9-11% natural ω-3–linolenic acid.
• The same transformation occurs during commercial deep-fat frying operations with canola oil. Thus canola oil used to fry French fries for seven hours per day for seven days at 185°C (365°F) resulted in increasing the total trans-fatty acid content of the oil from 2.4% to 3.3% by weight of total fat. [6]
• Of potentially greater concern is the formation of oxidation products of polyunsaturated fatty acids during prolonged commercial deep-fat frying. But this is less of a concern for canola oil than for oils with higher levels of more readily oxidized polyunsaturated fat such corn, soybean, sunflower, and safflower oils.

When considered in the context of other commercial fats, the low trans-fat content of canola oil is no different from other vegetable oils. But one word of caution is appropriate. Bottles of canola, soybean, and corn oil in the supermarket proudly proclaim “Contains zero grams of trans-fat.” Read the fine print that states zero grams of trans-fat per serving, which is only one tablespoon, or about 14 grams of oil. The FDA allows any component that is less than 0.5 grams per serving to be listed as zero grams! Despite this claim, virtually all vegetable oils sold in the supermarket contain small amounts (less than 5%) of trans-fat.

So what other options are there if one wants to avoid RBD oils?

Should a consumer want to avoid RBD oils, cold-pressed oils can be an option, since they are not treated with heat, not extracted with solvents, and not deodorized. [7] Depending on the type, these oils may feature a range of descriptions on their labels, such as “cold-pressed,” “unrefined,” “virgin,” etc. Due in part to their higher price point, adulteration of these types of oils (such as undisclosed “blending” with an RBD oil) has been an issue, so consumers looking to completely avoid RBD oils may also want to select high-quality oils from reputable sources, or those that have been verified to meet quality standards.*

Given the above information, is commercially processed canola oil harmful?

Although care must be taken in handling and processing of canola oil and other vegetable oils, canola oil is a safe and healthy form of fat that will reduce blood LDL cholesterol levels and heart disease risk compared to carbohydrates or saturated fats such as found in beef tallow or butter.  Indeed, in a randomized trial that showed one of the most striking reductions in risk of heart disease, canola oil was used as the primary form of fat. [8] Whether using cold-pressed canola oil provides some small additional benefit is not clear.

In general, variety is a good strategy in nutrition, and thus consuming a variety of oils is desirable, for example using extra virgin oil when the special flavor is desired and canola oil or soybean oil for other uses. Both canola and soybean oils provide ω-3 fatty acids that are important to include in an overall diet.  Of course, avoiding overheating and burning of oils is important to provide the best taste and to avoid damaging the healthy-promoting fatty acids that they contain.

 References

1. Swanson, R. G., Regents Professor, Department of Food Science, Washington State University, Hexane Extraction in Soyfoods Processing, 2009.
2. Health Canada, 2009, Guidance Documents, hc-sc.gc.ca.
3. Health Canada, 2006, Guidance Documents, hc-sc.gc.ca.
4. Azizian, H., and Kramer, J. K. G., A Rapid Method for the Quantification of Fatty Acids in Fats and Oil with Emphasis on trans Fatty Acids Using Fourier Transform Near Infrared Spectroscopy (FT-NIR), Lipids, 2005; 40:855-867.
5. Hénon, G., Kemény, Zs., Recseg, K., Zwobada, F., and Kovari, K., Deodorization of Vegetable Oils. Part I: Modeling the Geometrical Isomerization of Polyunsaturated Fatty Acids, J Am Oil Chem Soc 1999; 76:73-81.
6. Aladedunye, F. A., and Przybylski, R. Degradation and Nutritional Quality Changes of Oil During Frying, J Am Oil Chem Soc 2009; 86:149-156.
7. Gunstone, F. D., ed., Vegetable Oils in Food Technology: Composition, Properties and Uses, Blackstone Publishing, 2002.
8. de Lorgeril et al. Mediterranean alpha-linolenic acid-rich diet in secondary prevention of coronary heart disease Lancet 1994 Jun 11;343(8911):1454-9.

*Update 12/2018:
The original response to this question incorrectly stated that “regular olive oil is processed like other RBD oils.” Olive oil produced according to existing standards is a blend of olive oils that are mechanically extracted without the use of solvents, while RBD oils are generally extracted with solvents. Along with this correction, the discussion pertaining to this question was updated to reflect a broader range of options that may be available for consumers looking to avoid RBD oils.

 In December 2014 the Dietary Guidelines Advisory Committee (DGAC) released a preliminary document stating that “cholesterol is not considered a nutrient of concern for overconsumption,” suggesting that dietary cholesterol has little impact upon a person’s actual health status. Though the final report from the DGAC isn’t due until later in 2015, we checked in with Harvard T.H. Chan School of Public Health’s Walter Willett for some clarification on dietary cholesterol.

1. Cholesterol has long been considered a “bad” thing to eat. Even the first edition of the guidelines says avoid foods with too much cholesterol, because “eating extra saturated fat and cholesterol will increase blood cholesterol levels in most people.” How did this recommendation come about?

 The theory that cholesterol is a major factor in heart disease was attractive, but it turns out it was oversimplified. There was no direct evidence to support the link between egg consumption, for example, and heart disease.

2. Does that mean cholesterol-laden foods like cheese, red meat and eggs were wrongly vilified, or should people still limit consumption? Should we still care about cholesterol amounts in our food?

Some of those foods are definitely important to limit, but not simply because they have cholesterol in them. Poultry, for example, has a moderate amount of cholesterol, and so does fish – in fact all animal products do. Poultry and fish seem to be relatively healthy foods, and fish provides essential omega-3 fatty acids. That’s the problem with just looking at something as simple as one dietary factor like cholesterol; it doesn’t tell us the overall health impact of a food, and so we should be focusing more on the foods.

3. Even if dietary cholesterol doesn’t raise blood cholesterol levels, is it possible that other foods – like refined carbohydrates  – might raise cholesterol levels?

 Dietary cholesterol doesn’t raise blood cholesterol levels very much. It’s not that there’s no effect on blood cholesterol levels; there’s a small effect. It can raise both good and bad cholesterol in the blood so that makes it more complicated, and that’s why we need to look at the whole food, not just cholesterol content.

 The other main factor that increases blood cholesterol levels is saturated fat in the diet, and that actually has more of an impact than cholesterol in the diet. Then there are other aspects of the diet that can reduce cholesterol levels, specifically the bad cholesterol levels – for example unsaturated fat reduces blood cholesterol, and fiber can reduce blood cholesterol levels. Refined starches don’t have a major effect on bad cholesterol but they drop the good cholesterol. There are other aspects of diet that affect blood cholesterol, both the good and the bad parts of it.

4. For people who eat egg-substitute products that are both fat- and cholesterol-free, thinking that’s the “healthy” option, would you recommend switching back to real eggs?

It probably doesn’t make a huge difference for most people whether they eat eggs with or without the yolks. However, there is a caveat for people with diabetes. We have seen in repeated studies that higher egg consumption does increase risk of heart disease so we suggest that people with diabetes keep egg consumption and cholesterol intake low. Whether there are some other groups that might be more sensitive is still not clear.

5. As we see nutrition messages change over time – for example, fat used to be considered bad before we realized the health benefits of certain types of fats – and now the recommendation on cholesterol is changing, what should the general public take away from these kinds of shifts in dietary recommendations? What would you say in response to the recent New York Times article entitled “The Government’s Bad Diet Advice?”

The important point is to have the best possible evidence, and we shouldn’t be basing dietary guidance on just guesses or beliefs. In the case of both the egg issue and the total fat issue we were basically starting with virtually no direct evidence. When the evidence did start to come in – and there were different lines of evidence from our studies based on large cohorts and also short term studies investigating metabolic changes – it showed that people who consume more eggs did not have a higher risk of heart disease even after adjusting for any other factors, and that total fat in the diet was not related to heart disease risk or cancer risk. So it took those long term studies to show that those were not important factors, and that allowed us to modify the recommendations. We were really in a state 35 years ago in which we had very little direct evidence and we were basing guidelines on guesses and indirect evidence from very small, short term studies.

There are multiple problems with the article in The New York Times about the new Dietary Guidelines report that has done away with low-fat recommendations. It seems as if the author didn’t really read or understand the research that was mentioned. Although the Times story blames epidemiological research for recommendations to increase carbohydrate, the opposite is true. It’s actually largely our work which has led to the change eliminating the restriction on total fat intake. The author then goes on and makes her recommendations that we should be eating more red meat and high-fat dairy products, when there’s no evidence at all to support that, much less randomized trials, to support that conclusion.

One claim of the New York Times article was that we can only rely on clinical trials for information on diet and health. In theory we might like to have clinical trials to answer all such questions, but for issues that involve long term effects of diet that occur over many years and decades – for example, effects on heart disease and cancer – clinical trials have mainly been a failure because keeping people on specific diets over many years is difficult. So the theoretically perfect study will often just not be possible; therefore we have to use a combination of kinds of evidence. For most questions the best evidence will come from a combination of large cohort studies tracking the dietary habits and disease occurrence of participants over many years and small, short term studies in which a small number of participants are fed different diets and intermediate variables like blood pressure and cholesterol fractions are measured. This combination of evidence has been successful in identification of trans fat and soda as risk factors, has exonerated total fat and cholesterol as major risk factors, and also underlies guidelines on body weight and physical activity.

The Expert: Dr. Rob van Dam

The Summary

• Drinking up to six cups a day of coffee is not associated with increased risk of death from any cause, or death from cancer or cardiovascular disease.
• Some people may still want to consider avoiding coffee or switching to decaf, especially women who are pregnant, or people who have a hard time controlling their blood pressure or blood sugar.
• It’s best to brew coffee with a paper filter, to remove a substance that causes increases in LDL cholesterol.
• Coffee may have potential health benefits, but more research needs to be done.
• Read more about coffee and health

1. The latest Harvard study on coffee and premature mortality seems to offer good news for coffee drinkers. What did the research find?

We looked at the relationship between coffee consumption and overall mortality in the Nurses’ Health Study and the Health Professionals Follow-Up Study, which together included about 130,000 study volunteers. (1) At the start of the study, these healthy men and women were in their 40s and 50s. We followed them for 18 to 24 years, to see who died during that period, and to track their diet and lifestyle habits, including coffee consumption. We did not find any relationship between coffee consumption and increased risk of death from any cause, death from cancer, or death from cardiovascular disease. Even people who drank up to six cups of coffee per day were at no higher risk of death. Consistent with our findings, recent meta-analyses that combined data from all published prospective studies on coffee and risk of cardiovascular diseases (2) or premature mortality (3) did not show any increase in risk for high coffee consumption as compared with non-consumption. These findings fit into the research picture that has been emerging over the past few years: For the general population, the evidence suggests that coffee drinking doesn’t have any serious detrimental health effects.

2. So for coffee drinkers, no news is good news? Why is this finding so important?

It’s an important message because people have seen coffee drinking as an unhealthy habit, along the lines of smoking and excessive drinking, and they may make a lot of effort to reduce their coffee consumption or quit drinking it altogether, even if they really enjoy it. Our findings suggest that if you want to improve your health, it’s better to focus on other lifestyle factors, such as increasing your physical activity, quitting smoking, or eating more fruit, vegetables, nuts and whole grains.

 3. Is there an upper limit for the amount of coffee that is healthy to drink each day?

If you’re drinking so much coffee that you get tremors, have sleeping problems, or feel stressed and uncomfortable, than obviously you’re drinking too much coffee. But in terms of effects on mortality or risk of chronic diseases, we don’t see any negative effects of consuming up to six cups of coffee a day. Keep in mind that our study and in most studies of coffee, a “cup” of coffee is an 8-ounce cup with 100 mg of caffeine, not the 16 ounces you would get in a grande coffee at a Starbucks, which has about 330 mg of caffeine.

Also keep in mind that the research is typically based on coffee that’s black or with a little milk or sugar, but not with the kind of high-calorie coffeehouse beverages that have become popular over the past few years. A 24-ounce mocha Frappachino at Starbucks with whipped cream has almost 500 calories—that’s 25 percent of the daily calorie intake for someone who requires 2,000 calories a day. People may not realize that having a beverage like that adds so much to their energy intake, and they may not compensate adequately by eating less over the course of the day. This could lead to weight gain over time, which could in turn increase the risk of type 2 diabetes, and that’s a major concern.

 4. Is there any research that suggests coffee may have some beneficial health effects?

Yes, results of research over the past decade suggest that coffee consumption may protect against type 2 diabetes (4), Parkinson’s disease (5), and liver cancer (6). For example, the link between coffee consumption and risk of type 2 diabetes has been evaluated in more than 25 cohort studies from America, Europe, and Asia and results from nearly all of these studies suggest that coffee may lower diabetes risk.(4) Interestingly, similar results were observed for caffeinated and decaffeinated coffee suggesting that compounds other than caffeine may lower risk of diabetes. In addition, our recent meta-analysis on coffee consumption and cardiovascular diseases suggested that moderate coffee consumption (3-5 small cups per day) is linked to a slightly lower risk of cardiovascular diseases.(2) This is an active area of research right now, and it’s not at the stage where we would say, ”Start drinking coffee to increase your health even if you don’t like it.” But I think the evidence is good that for people in general—outside of a few populations, such as pregnant women, or people who have trouble controlling their blood pressure or blood sugar—coffee is one of the good, healthy beverage choices.

 5. Why does it seem like scientists keep flip-flopping on whether coffee is bad for you or good for you?

Often people think of coffee just as a vehicle for caffeine. But it’s actually a very complex beverage with hundreds of different compounds in it. Since coffee contains so many different compounds, drinking coffee can lead to diverse health outcomes. It can be good for some things and bad for some things, and that’s not necessarily flip-flopping or inconsistent. That’s why we do studies on very specific health effects—for example, studies of how coffee affects the risk of diabetes—but we also conduct studies looking at coffee consumption and mortality over a long period of time, which better reflects the overall health effect.

Coffee is also a bit more complex to study than some other food items. Drinking coffee often goes along with cigarette smoking, and with a lifestyle that’s not very health conscious. For example, people who drink lots of coffee tend to exercise less and have a less healthful diet. So in the early studies on coffee and health, it was difficult to separate the effects of coffee from the effects of smoking or other lifestyle choices.

Over the several decades that coffee has been studied, there have been some reports that coffee may increase the risk of certain cancers or the risk of heart disease. But in better conducted studies—larger studies that have a lot of information about all other lifestyle factors and make a real effort to control for these lifestyle factors—we do not find many of these health effects that people were concerned about.

 6. What is the latest research on the risks of coffee or caffeine during pregnancy?

For pregnant women, there has been quite a bit of controversy over whether intake of coffee or caffeine has detrimental effects on the fetus. The jury is still out, but the best currently available evidence does suggest that caffeine intake during pregnancy can reduce fetal growth and may even increase risk of miscarriage or stillbirth (7-8). It is known that caffeine crosses the placenta and reaches the fetus, and that the fetus is very sensitive to caffeine; it metabolizes it very slowly. So for pregnant women it seems prudent to abstain from caffeinated coffee or reduce their caffeine intake to a low level, for example one small cup a day.

 7. Should people with high blood pressure consider reducing their coffee or caffeine intake? What about people with diabetes?

We know that if people are not used to using any caffeine, and they start to use caffeine, their blood pressure goes up substantially. Within a week of caffeine consumption, however, we see that the effect is less pronounced—habituation occurs and there is less of an increase in blood pressure. After several weeks of continued caffeine consumption, however, a small increase in blood pressure remains (9). In studies that look at the incidence of hypertension in the general population, drinking caffeinated coffee is not associated with a substantial increase in risk.(10) But if people have hypertension, and are having a hard time controlling their hypertension, they could try switching from caffeinated coffee to decaffeinated coffee, to see if it has a beneficial effect.

With diabetes, it’s a bit of a paradox. Studies around the world consistently show that high consumption of caffeinated or decaffeinated coffee is associated with low risk of type 2 diabetes (4). But if you look at acute studies that just give people caffeine or caffeinated coffee, and then have them eat something high in sugar, their sensitivity to insulin drops and their blood glucose levels are higher than expected.(11) There isn’t any long-term data on coffee consumption and glucose control. But if people have diabetes and have trouble controlling their blood glucose, it may be beneficial for them to try reducing their coffee consumption or switching from caffeinated to decaffeinated coffee.

8. How do you explain the paradoxical findings on coffee and caffeine consumption and diabetes?

It’s possible that there are simply different effects for short-term and long-term intake of coffee and caffeine. And, as I mentioned before, it’s becoming increasingly clear that coffee is much more than caffeine, and the health effects that you see for caffeinated coffee are often different than what you would expect based on its caffeine content.

For example, if you look at exercise performance, it seems that caffeine can be somewhat beneficial, but caffeinated coffee is not. Or if you look at blood pressure and compare the effects of caffeinated coffee to the effects of caffeine, you’ll find that caffeinated coffee causes blood pressure increases that are substantially weaker than what one would expect for the amount of caffeine it contains (9). The same is true for the relationship between coffee, caffeine, and blood glucose after a meal. It’s possible that there are compounds in coffee that may counteract the effect of caffeine, but more research needs to be done.

 9. Is drinking coffee made with a paper filter healthier than drinking boiled coffee or other types of coffee?

Coffee contains a substance called cafestol that is a potent stimulator of LDL-cholesterol levels (12). Cafestol is found in the oily fraction of coffee, and when you brew coffee with a paper filter, the cafestol gets left behind in the filter. Other methods of coffee preparation, such as the boiled coffee common in Scandinavian countries, French press coffee, or Turkish coffee, are much higher in cafestol. So for people who have high cholesterol levels or who want to prevent having high cholesterol levels, it is better to choose paper filtered coffee or instant coffee, since they have much lower levels of cafestol than boiled or French press coffee. Espresso is somewhere in the middle; it has less cafestol than boiled or French press coffee, but more than paper filtered coffee.

10. Do tea and coffee have similar beneficial effects?

Tea is also a prudent low-calorie beverage choice. The results from several studies suggest that tea consumption is also linked to a lower risk of type 2 diabetes, but overall the results for tea have been less consistent than for coffee.(13) Consumption of green tea may have other health benefits such as lowering blood pressure and serum cholesterol concentrations.(14)

Related

Coffee

Coffee lovers around the world who reach for their morning brew probably aren’t thinking about its health benefits or risks. And yet this beverage has been subject to a long history of debate.

References

1. Lopez-Garcia E, van Dam RM, Li TY, Rodriguez-Artalejo F, Hu FB. The Relationship of Coffee Consumption with Mortality. Ann Intern Med. 2008;148:904-914.

2. Crippa A, Discacciati A, Larsson SC, Wolk A, Orsini N. Coffee consumption and mortality from all causes, cardiovascular disease, and cancer: a dose-response meta-analysis. Am J Epidemiol. 2014;180:763-75.

3. Ding M, Bhupathiraju SN, Chen M, van Dam RM, Hu FB. Caffeinated and decaffeinated coffee consumption and risk of type 2 diabetes: a systematic review and a dose-response meta-analysis. Diabetes Care. 2014;37:569-86.

4. Ding M, Bhupathiraju SN, Satija A, van Dam RM, Hu FB. Long-term coffee consumption and risk of cardiovascular disease: a systematic review and a dose-response meta-analysis of prospective cohort studies. Circulation. 2014;129:643-59.

5. Qi H, Li S. Dose-response meta-analysis on coffee, tea and caffeine consumption with risk of Parkinson’s disease. Geriatr Gerontol Int. 2014;14:430-9.

6. Bravi F, Bosetti C, Tavani A, Gallus S, La Vecchia C. Coffee reduces risk for hepatocellular carcinoma: an updated meta-analysis. Clin Gastroenterol Hepatol. 2013;11:1413-1421.e1.

7. Chen LW, Wu Y, Neelakantan N, Chong M, Pan A, van Dam RM. Maternal caffeine intake during pregnancy is associated with risk of low birth weight: a systematic review and dose-response meta-analysis. BMC Med. 2014;12:174.

8. Greenwood DC, Thatcher NJ, Ye J, Garrard L, Keogh G, King LG, Cade JE. Caffeine intake during pregnancy and adverse birth outcomes: a systematic review and dose-response meta-analysis. Eur J Epidemiol. 2014;29:725-34.

9. Noordzij M, Uiterwaal CS, Arends LR, Kok FJ, Grobbee DE, Geleijnse JM. Blood pressure response to chronic intake of coffee and caffeine: a meta-analysis of randomized controlled trials. J Hypertens. 2005;23:921-8.

10. Winkelmayer WC, Stampfer MJ, Willett WC, Curhan GC. Habitual caffeine intakeand the risk of hypertension in women. JAMA. 2005;294:2330-5.

11. Lane JD, Feinglos MN, Surwit RS. Caffeine increases ambulatory glucose and postprandial responses in coffee drinkers with type 2 diabetes. Diabetes Care 2008;31:221-2.

12. Urgert R, Katan MB. The cholesterol-raising factor from coffee beans. Annu Rev Nutr. 1997;17:305-24.

13. Yang WS, Wang WY, Fan WY, Deng Q, Wang X. Tea consumption and risk of type 2 diabetes: a dose-response meta-analysis of cohort studies. Br J Nutr. 2014;111:1329-39.

14.Onakpoya I, Spencer E, Heneghan C, Thompson M. The effect of green tea on blood pressure and lipid profile: a systematic review and meta-analysis of randomized clinical trials. Nutr Metab Cardiovasc Dis. 2014;24:823-36.