Scientific Update

A Review of Recent Scientific Papers Related to Vegetarianism

By Reed Mangels, PhD, RD

Long-Term Studies of Vegetarians in the Past 35 Years

In the past 35 years, at least six large-scale, long-term studies of vegetarian adults have been conducted. Some studies examine different kinds of vegetarians (lacto-ovo and vegan, for example) and some studies often include non-vegetarians for comparison purposes. Study subjects are asked about their diets and their health and are often given follow-up questionnaires every few years for the duration of the study. These studies can last 20 or more years, so they offer an opportunity to learn a lot about changes in health over time. Subjects make their own choices about diet, exercise, and other factors. Their reports of health issues may be checked using medical records or other records like death registries. These studies provide us with a great deal of information about vegetarian health and mortality and have changed the way that many healthcare professionals think about vegetarian diets.

Vegetarian diets are being recommended for prevention and treatment of many chronic diseases, including obesity, type 2 diabetes, heart disease, and high blood pressure — in large part due to the findings of these large, long-term studies.

The Adventist Health Studies have examined vegetarian and non-vegetarian Seventh-day Adventists. The results of these studies are especially interesting because they look at a population that is not likely to smoke or to use alcohol and that has good social support systems. Even in this healthy population, following a vegetarian diet can be an advantage.

Adventist Health Study-1 (AHS-1) was started in 1974. More than 28,000 non-Hispanic white Adventist adults living in California participated in this study which lasted until 1988.1 About 30% of study subjects were classified as vegetarian (no meat, poultry, or fish). Only about 2-3% of Adventists were vegan during the years when this study was conducted.

Adventist Health Study-2 (AHS-2) is even more ambitious in scope. This study was started in 2001 and includes 96,000 Adventists living in the U.S. and Canada. About 65% of the subjects are non-Hispanic Whites and 27% are Black/African Americans. Subjects are contacted every two years and are asked to complete surveys about their health and lifestyle. At the beginning of the study, 8% of subjects were categorized as vegan (eating any animal products less than once a month), 29% as lacto-ovo vegetarian (meat or fish less than 4 times per month), 10% regularly ate fish but not meat, and 53% regularly ate meat, poultry, and fish.2 This study is still going on.

In Europe, there have been at least four large-scale studies that included significant numbers of vegetarians in the past 35 years. These studies differ from the Adventist studies because they do not focus on a single religious group. The oldest of these studies is the Health Food Shopper Study which began in 1973. Almost 11,000 study subjects were recruited through health food stores and vegetarian groups. About one third were vegetarians, mainly lacto-ovo vegetarians.3 The Oxford Vegetarian Study also had about 11,000 subjects, 42% of whom were vegetarians. The study began in 1980 and subjects were followed for 20 years.4 The German Vegetarian Study began in 1978 and had around 1900 participants; about 60% were vegetarian.5

EPIC-Oxford is a huge study of more than 65,000 vegetarians and nonvegetarians that has been conducted in the UK since 1993. About 30% of subjects are lacto-ovo vegetarian and 4% are vegan.6 Information is still being collected from this study.

Here's a smattering of what we've learned from these studies:

  • Vegetarians have a lower risk of having heart disease than do people who eat meat or fish.7 Vegetarians are also less likely to die from heart disease.7,8
  • Vegetarians had a lower risk of some cancers,9 although the difference in risk of dying from cancer is not significantly different in vegetarians compared to nonvegetarians.10
  • Vegetarians have a lower risk of having hypertension1,2 and type 2 diabetes.1,2
  • Vegetarians have a lower BMI1,6,11 and gain less weight in adulthood than do nonvegetarians.12 The lowest average BMIs are seen in vegans.13,14
  • Vegetarians have lower risks of diverticular disease,14 cataracts, kidney stones, and hyperthyroidism12 than nonvegetarians.
  • Adequate calcium15 and protein16 may reduce the risk of bone fractures.

As I think about these studies, I am grateful to the researchers for their efforts to recruit subjects and to collect and analyze data. I am grateful to the study subjects who completed many questionnaires and examinations. The results of these studies have helped to change the way that the general public and healthcare providers think about vegetarian diets.

  1. Fraser GE. 1999. Associations between diet and cancer, ischemic heart disease, and all-cause mortality in non-Hispanic white California Seventh-day Adventists. Am J Clin Nutr. 70:532S-8S.
  2. Orlich MJ, Fraser GE. 2014. Vegetarian diets in the Adventist Health Study 2: a review of initial published findings. Am J Clin Nutr. 100:353S-8S.
  3. Burr ML, Sweetnam PM. 1982. Vegetarianism, dietary fiber, and mortality. Am J Clin Nutr. 36:873-7.
  4. Appleby PN, Thorogood M, Mann JI et al. 1999. The Oxford Vegetarian Study: an overview. Am J Clin Nutr. 70:525S-31S.
  5. Chang-Claude J, Frentzel-Beyme R, Eilber U. 1992. Mortality pattern of German vegetarians after 11 years of follow-up. Epidemiology. 3:395-401.
  6. Davey GK, Spencer EA, Appleby PN, et al. 2003. EPIC-Oxford lifestyle characteristics and nutrient intake in a cohort of 33,883 meat-eaters and 31,546 non meat-eaters in the UK. Public Health Nutr. 6:259-68.
  7. Crowe FL, Appleby PN, Travis RC, Key TJ. 2013. Risk of hospitalization or death from ischemic heart disease among British vegetarians and nonvegetarians: results from the EPIC-Oxford cohort study. Am J Clin Nutr. 97:597-603.
  8. Key TJ, Fraser GE, Thorogood M, et al. 1999. Mortality in vegetarians and nonvegetarians: detailed findings from a collaborative analysis of 5 prospective studies. Am J Clin Nutr. 70:516S-24S.
  9. Key TJ, Appleby PN, Crowe FL, et al. 2014. Cancer in British vegetarians: updated analysis of 4998 incident cancers in a cohort of 32,491 meat eaters, 8612 fish eaters, 18,298 vegetarians, and 2246 vegans. Am J Clin Nutr. 100:378S-85S.
  10. Orlich MJ, Singh PN, Sabaté J, et al. 2014. Vegetarian dietary patterns and mortality in Adventist Health Study 2. JAMA Intern Med. 173:1230-8.
  11. Tonstad S, Butler T, Yan R, et al. 2009. Type of vegetarian diet, body weight, and prevalence of type 2 diabetes. Diabetes Care. 32:791-6.
  12. Appleby PN, Key TJ. 2016. The long-term health of vegans and vegetarians. Proc Nutr Soc. 75:287-93.
  13. Spencer EA, Appleby PN, Davey GK, Key TJ. 2003. Diet and body mass index in 38,000 EPIC-Oxford meat-eaters, fish-eaters, vegetarians, and vegans. Int J Obes Relat Metab Disord. 27:728-34.
  14. Crowe FL, Appleby PN, Allen NE, Key TJ. 2011. Diet and risk of diverticular disease in Oxford cohort of European Prospective Investigation into Cancer and Nutrition (EPIC): prospective study of British vegetarians and non-vegetarians. BMJ. 343:4131.
  15. Appleby P, Roddam A, Allen N, et al. 2007. Comparative fracture risk in vegetarians and nonvegetarians in EPIC-Oxford. Eur J Clin Nutr. 61:1400-6.
  16. Thorpe DL, Knutsen SF, Beeson WL, et al. 2008. Effects of meat consumption and vegetarian diet on risk of wrist fracture over 25 years in a cohort of peri- and postmenopausal women. Public Health Nutr. 11:564-7