Vegetarian Diets May Protect Against Obesity, Type 2 Diabetes

Laurie Barclay, MD

May 14, 2009

May 14, 2009 — Vegan and vegetarian diets may protect against obesity and type 2 diabetes, according to the results of a cohort study reported in the May issue of Diabetes Care.

"The European Prospective Investigation found that BMI [body mass index] was highest in meat eaters, lowest in vegans, and intermediate in fish eaters," write Serena Tonstad, MD, PhD, from Loma Linda University in Loma Linda, California, and colleagues. "The protective effects of vegetarianism against overweight may be due to avoidance of major food groups, displacement of calories toward food groups that are more satiating, or other factors. Based on a review of experimental data, investigators have suggested that the portfolio of foods found in vegetarian diets may carry metabolic advantages for the prevention of type 2 diabetes."

The goal of this study was to compare the prevalence of type 2 diabetes in people following different types of vegetarian diets vs that in nonvegetarians, using a study cohort of 22,434 men and 38,469 women enrolled in the Adventist Health Study-2 conducted from 2002 to 2006.

Seventh-Day Adventist church members across North America provided self-reported demographic, anthropometric, medical history, and lifestyle data, and a food-frequency questionnaire was used to categorize the type of vegetarian diet. Multivariate-adjusted logistic regression allowed calculation of odds ratios (ORs) and 95% confidence intervals [CIs].

Vegans had the lowest BMI (23.6 kg/m2). There was a progressive increase in BMI with increased content of animal products in the diet: 25.7 kg/m2 in lacto-ovo vegetarians, 26.3 kg/m2 in pesco-vegetarians, 27.3 kg/m2 in semi-vegetarians, and 28.8 kg/m2 in nonvegetarians.

The prevalence of type 2 diabetes also increased with increasing consumption of animal products: 2.9% for the vegan diet, 3.2% for the lacto-ovo diet, 4.8% for the pesco-vegetarian diet, 6.1% for the semi-vegetarian diet, and 7.6% for the nonvegetarian diet.

Compared with nonvegetarians, vegetarians had a lower risk for type 2 diabetes, after adjustment for age, sex, ethnicity, education, income, physical activity, television watching, sleep habits, alcohol use, and BMI. The OR was 0.51 for vegans (95% CI, 0.40 - 0.66), 0.54 for lacto-ovo vegetarians (95% CI, 0.49 - 0.60), 0.70 for pesco-vegetarians (95% CI, 0.61 - 0.80), and 0.76 for semi-vegetarians (95% CI, 0.65 - 0.90).

Limitations of this study include lack of data on glycemic load of the diets; cross-sectional data, precluding drawing of causal inferences; inability to assess physical activity for approximately one sixth of the cohort; measurement errors involved in food-frequency questionnaires; all variables self-reported; the possibility that diabetes may have been underreported in the vegan and other vegetarians because of their lower BMIs; and cohort not representative of the general population.

"The 5-unit BMI difference between vegans and nonvegetarians indicates a substantial potential of vegetarianism to protect against obesity," the study authors write. "Increased conformity to vegetarian diets protected against risk of type 2 diabetes after lifestyle characteristics and BMI were taken into account. Pesco- and semi-vegetarian diets afforded intermediate protection."

The National Institutes of Health and the School of Public Health, Loma Linda University, supported this study. The study authors have disclosed no relevant financial relationships.

Diabetes Care. 2009;32:791-796.

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