Eat Plant-Based Foods for Health

by Sharon Palmer, R.D.

People who eat a plant-based diet live longer, have less cancer and heart disease, weigh less, and have healthier diets. They even have a lower carbon footprint. These were the impressive findings from the landmark study Adventist Health Study-2 (AHS-2), which were announced at the International Congress of Vegetarian Nutrition at Loma Linda University in California in February 2013.

What's so special about the Adventist Health Study?

AHS-2 is the culmination of more than 50 years of research conducted at Loma Linda University on members of the Seventh-day Adventist religious denomination. The Adventists garnered interest among researchers due to their healthful lifestyle, which includes abstinence from cigarettes and alcohol, and high rates of vegetarianism -- 35 percent are vegetarian, compared to about 4 percent in the general population. Within this group is a wide range of dietary patterns, from strict vegan to non-vegetarian, making this group a researcher's dream -- scientists are able to study the effects of dietary patterns without the impact of other factors, such as smoking and alcohol.

The first Adventist Health Study (AHS-1, 1974-1988) examined risk of cancer and cardiovascular disease among 34,000 people. AHS-2, with 96,000 Adventist participants, was even more ambitious: Beginning in 2002, Loma Linda University scientists compared the impact of various diet patterns within the same study population, making it one of the most comprehensive diet studies ever conducted. Data was gathered as subjects from all over the U.S. and Canada completed 50-page questionnaires about diet, lifestyle and health.

The definition of a plant-based diet is not rigid; it simply means a diet that focuses on plants. Thus, someone who eats small amounts of animal foods can fit within this definition, as can someone who is a strict vegan and eats no animal foods. What makes AHS-2 unique is that scientists examined the effects of different plant-based diets within the study population.

The five diet patterns in AHS-2 were broken down as follows:

1. Vegans who eat no animal products

2. Lacto-ovo vegetarians, who eat no meat but do eat eggs or dairy foods or both

3. Pesco-vegetarians, who eat fish but other meats one or fewer times per month

4. Semi-vegetarians, who eat meats aside from fish occasionally but less than weekly

5. Non-vegetarians, who eat meats aside from fish at least one time per week

Until this study, there was little knowledge about the daily intake of plant-based eaters. Gary Fraser, PhD, MPH, who led the AHS-2 research team at Loma Linda University, spoke about the study findings -- both published and unpublished -- at the congress. He reported that for many years, researchers were convinced that various types of vegetarian diets were responsible for only moderate differences in health outcome, because there was inadequate research on plant-based diets. But in AHS-2, "We saw huge differences in food intake among the different vegetarian dietary patterns," said Fraser.

Fraser reported many interesting observations about various dietary patterns, including:

Plant protein.

Soy protein and plant protein intake is much greater in vegans than in non-vegetarians.

Omega-3 fatty acids.

While the omega-3 fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid) intake is much lower among vegans and vegetarians, the plant omega-3 fatty acid ALA (alpha-linolenic acid) is higher in this group (about 2 grams per day), and higher levels of EPA and DHA are found in their body fat, suggesting high intake of plant omega-3s may result in higher levels in the body.

Saturated fat.

Intake is very low in vegans.

Micronutrients.

Beta-carotene and vitamin C intake is much higher in vegans. Vitamin B12 intake in vegans is low, but they often supplement this nutrient. Iron intake is good for vegans through the diet, as they do not typically supplement this nutrient. Calcium intake is very low in vegans, but not in lacto-ovo vegetarians.

As the scientists began to compare the health outcomes of the various diet patterns in AHS-2, they saw something intriguing. For many health outcomes, a progressively beneficial relationship was observed between the dietary patterns, with vegan providing the best benefit compared with non-vegetarian, followed by lacto-ovo vegetarian, pesco-vegetarian, and semi-vegetarian.

In other words, the more plant-based the diet, the greater the benefit. Fraser presented the following findings:

Weight.

A progressive weight increase was seen from a vegan diet toward a non-vegetarian diet. "The average body mass index (BMI) for vegans was 23.6, lacto-ovo vegetarians 25.7, pesco-vegetarians 26.3, semi-vegetarians 27.3, and non-vegetarians 28.8," said Fraser (Journal of the Academy of Nutrition and Dietetics, December 2013). BMI over 25 is overweight; over 30 is obese.

Cardiovascular disease.

The same trend was observed for cardiovascular disease markers, such as levels of cholesterol, and incidence of high blood pressure and metabolic syndrome, with the vegan dietary pattern offering the lowest risk compared with non-vegetarian (Diabetes Care, 2012).

Type 2 Diabetes.

Prevalence of type 2 diabetes among vegans (2.9 percent) and lacto-ovo vegetarians (3.2 percent) was half that of non-vegetarians (7.6 percent), reported Fraser, who also noted that the same trend prevailed in fasting blood glucose levels.

Inflammation.

A similar trend, progressing from vegan to non-vegetarian, was observed for C-reactive protein, a measure of inflammation, which is considered a root of chronic disease.

Cancer.

Fraser reported, "For overall cancer, all vegetarians (vegans plus lacto-ovo vegetarians) had an 8 percent reduction in risk, and vegans did best of all. For gastrointestinal cancers, vegetarians as a group had 24 percent reduction in risk, and in particular lacto-ovo vegetarians did the best. For respiratory system cancers, the vegetarian group had a 23 percent reduction in risk. In female cancers, vegans did the best in reduced risk."

Longevity.

"Death rates rise across the dietary groups, from vegans to non-vegetarians," said Fraser. There was a 12 percent reduction in risk of all-cause mortality in all vegetarians combined vs. non-vegetarians, with a reduction in risk of 15 percent in vegans compared with non-vegetarians, 9 percent in lacto-ovo vegetarians, 19 percent in pesco-vegetarians, and 8 percent in semi-vegetarians (JAMA Intern Med, 2013).

Carbon footprint.

Vegetarian diets are also more sustainable, according to Joan Sabate, MD, DrPh, chair of nutrition at Loma Linda University, who spoke at the congress. According to a life cycle assessment applied to the AHS-2 data, Sabate reported that the greenhouse gas emissions for a vegan diet are 41.7 percent lower compared with non-vegetarians; lacto-ovo vegetarians are 27.8 percent lower, pescatarians are 23.8 percent lower, and semivegetarians are almost 20 percent lower.

Healthy behaviors.

Compared to non-vegetarians, vegans and vegetarians watch less television, sleep more, and consume more fruits, vegetables, and low-glycemic foods and less saturated fat.

Adventist Health Study 2

In this video, Gary Fraser, Adventist Health Study principle investigator, shares findings from Adventist Health Study 2.

"Eat Plant-Based Foods for Health"