Abstract
Vegetarians, those who avoid meat, and vegans, additionally avoiding dairy and eggs, represent 5% and 2%, respectively, of the US population. The aim of this review is to assess the effects of vegetarian diets, particularly strict vegetarian diets (i.e., vegans) on health and disease outcomes. We summarized available evidence from three prospective cohorts of Adventists in North America: Adventist Mortality Study, Adventist Health Study, and Adventist Health Study-2. Non-vegetarian diets were compared to vegetarian dietary patterns (i.e., vegan and lacto-ovo-vegetarian) on selected health outcomes. Vegetarian diets confer protection against cardiovascular diseases, cardiometabolic risk factors, some cancers and total mortality. Compared to lacto-ovo-vegetarian diets, vegan diets seem to offer additional protection for obesity, hypertension, type-2 diabetes, and cardiovascular mortality. Males experience greater health benefits than females. Limited prospective data is available on vegetarian diets and body weight change. Large randomized intervention trials on the effects of vegetarian diet patterns on neurological and cognitive functions, obesity, diabetes, and other cardiovascular outcomes are warranted to make meaningful recommendations.
Generated Summary
This review article assesses the health effects of vegetarian diets, particularly strict vegetarian diets (i.e., vegans), on health and disease outcomes. The study summarized evidence from three prospective cohorts of Adventists in North America: Adventist Mortality Study, Adventist Health Study, and Adventist Health Study-2. The researchers compared non-vegetarian diets to vegetarian dietary patterns (i.e., vegan and lacto-ovo-vegetarian) on selected health outcomes. The goal was to determine whether vegetarian diets offer protection against cardiovascular diseases, cardiometabolic risk factors, certain cancers, and overall mortality. The methodology included an independent literature review using PubMed/Medline and EMBASE databases to identify relevant articles. The search terms included various combinations of “Adventist,” “vegetarian,” “vegan,” and specific health outcomes such as cancer, diabetes, and mortality. Inclusion criteria were large prospective cohort studies of Adventists, reports with clearly defined dietary patterns as exposures, and data of vegetarians compared to non-vegetarians. Exclusion criteria were animal studies, case studies with small sample sizes, and studies reporting only nutrients or food groups. Data abstraction and tabulation followed pre-established criteria related to dietary pattern classification and characteristics of the study cohorts.
Key Findings & Statistics
- Vegetarians (those avoiding meat) and vegans (additionally avoiding dairy and eggs) represent 5% and 2%, respectively, of the US population.
- In a recent Gallup Poll (2012), 5% of the American adult population is vegetarian, and 2% reported adopting a vegan diet.
- For BMI, vegetarians were approximately 2–4 points lower than non-vegetarians.
- Vegetarians had 55% lower odds of developing hypertension.
- The odds of developing type-2 diabetes was 25% to 49% lower for vegetarians.
- The odds of developing metabolic syndrome (MetS) for vegetarians were about half compared to non-vegetarians.
- Overall cancer risk reduction for vegetarians was 8%.
- Vegetarians had approximately half the risk of developing colon cancer.
- Vegetarians had 23% risk reduction for cancer of the gastrointestinal tract.
- Vegetarians experienced a 35% risk reduction for prostate cancer.
- Vegetarians experienced a 10% to 20% decreased in all-cause mortality.
- Vegetarians had 26% to 68% lower risks of mortality from ischemic heart disease, cardiovascular disease, and cerebrovascular disease.
- Lacto-ovo-vegetarians experienced a 9% risks reduction for all-cause total mortality.
- Vegan had 14% lower risks of all-cause mortality in males.
- Lacto-ovo-vegetarian and vegan males experienced a 23% and 42% risks reduction in CVD mortality, respectively.
- Vegan males also had a 55% risk reduction for ischemic heart disease.
Other Important Findings
- Vegetarian diets confer protection against cardiovascular diseases, cardiometabolic risk factors, and some cancers.
- Vegan diets seem to offer additional protection for obesity, hypertension, type-2 diabetes, and cardiovascular mortality compared to lacto-ovo-vegetarian diets.
- Males experience greater health benefits than females.
- Studies of Adventists have provided compelling evidence that well-balanced vegetarian diets are nutritionally adequate and associated with a lower risk of chronic diseases.
- For hypertension, lacto-ovo-vegetarians experienced 55% lower risks; whereas, vegans had 75% risks reduction.
- Lacto-ovo-vegetarian and vegan were associated with lower risks of type-2 diabetes.
- Vegans experienced modest risks reduction (14%) for all-cancer.
Limitations Noted in the Document
- The findings may not be fully generalizable to other vegetarians with different lifestyles.
- The studies did not directly compare vegans with lacto-ovo-vegetarians.
- Observed health benefits may be partially related to other lifestyle factors.
- Dietary patterns may change over time, which was not accounted for.
- The relatively low intake of meat by the reference group in this cohort may result in smaller observed effects.
- Relative small sample size within the vegan groups may limit conclusions.
- The research has mostly derived from observational studies.
Conclusion
The studies of North American Adventists suggest vegetarian diets are associated with lower risks for cardiometabolic outcomes and certain cancers. Furthermore, greater avoidance of eggs and dairy products may offer an additional benefit. Vegan diets appear to provide greater protection against obesity, hypertension, type-2 diabetes, and cardiovascular mortality compared to lacto-ovo-vegetarian diets. The protective effects of vegetarian diets are generally more pronounced in men. The consistent findings across the Adventist cohorts regarding the benefits of vegetarian diets, specifically for cardiovascular disease, warrant further investigation and validation through large randomized dietary intervention trials. The article also highlights that vegetarians have a lower risk of many diseases, resulting in greater life-expectancy compared to non-vegetarians, with Adventist males living longer than the general population. The results suggest the need for additional investigation of neurological and cognitive disorders and other health effects. The observed lower risk for cardiovascular disease and cancer for those on plant-based diets, underscore the importance of ongoing research and the potential for these diets in healthcare, as well as nutritional planning.
IFFS Team Summary
- Excellent Review Article on Adventist Studies up until 2014
- Shows benefits for all cause mortality, cancers, cardiovascular disease, and health parameters of plant based diets
- Some data is statistically significant, and others remain to be determined as the current Adventist 2 cohort is observed for a longer period
- Effect is greater in males vs females
- Stronger Data in earlier studies, my belief is that diet had a greater effect when there was less primary prevention, secondary prevention, and treatment options for cancer, cardiovascular disease, cerebrovascular disease, and metabolic diseases.