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Body Mass Index

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Figure 5.2 Distribution in five categories of BMI of vegetarians and non-vegetarians of the Adventist Health Study cohort.

Body Mass Index

Figure 5.2 Distribution in five categories of BMI of vegetarians and non-vegetarians of the Adventist Health Study cohort.

in men (Figure 5.3). A higher proportion of meat eaters than non-meat eaters were overweight or obese (21% vs. 10% of men and 13% vs. 8% of women), whereas a lower proportion of meat eaters had a BMI < 20kg/m2 (9% vs. 17% of men and 18% vs. 33% of women). No significant differences in BMI values were observed in this study between "long-term vegetarians" (5 years or more) and those who had recently given up meat.

Figure 5.3 Oxford Vegetarian Study cohort. Comparison of BMI of vegetarians and non-vegetarians by gender and age.

Meat eaters consumed significantly more animal fat and alcoholic beverages and less dietary fiber than non-meat eaters. After adjusting for these dietary factors and other life-style factors, the differences in BMI between meat eaters and non-meat eaters were reduced by 33%, but were still present. Thus, these confounding factors do not fully explain the role of vegetarian diets on obesity prevention, suggesting an independent effect for low meat intake. In a cohort of about 20,000 vegetarians in Germany, an inverse relationship was also observed between BMI and vegetarian status. Strict vegetarians, those who avoided meat completely, were thinner than the occasional meat-eaters.18

Key & Davey12 used data from approximately 4000 men and women collected in England for the European prospective investigation into cancer and nutrition (EPIC study) to examine the relationship between obesity and meat intake. Subjects were classified as meat eaters if they ate any meat, as fish eaters if they did not eat meat but did eat fish, as vegetarians if they did not eat meat or fish but did eat dairy products or eggs, and as vegans if they did not eat any of these four categories of food. Among both men and women, mean BMI was highest among meat eaters, lowest among the vegans, and intermediate among the fish eaters and vegetarians. These differences in body mass index are equivalent to mean differences in weight between meat eaters and vegans of 5.9 kg in men and 4.7 kg in women. In the groups that did not eat meat, mean BMI was lower among those who had adhered to their diet for 5 or more years than among those who had adhered to their diet for a shorter period. According to the authors, this association with duration of the diet patterns suggests that the differences in BMI are largely due to the qualitative differences between the diets of the four groups. Among the meat eaters, about 6.1% of the men and 9.1% of the women were clinically obese (BMI > 30). In contrast, the prevalence of obesity was about three times lower for vegans (2% for men and less than 4% for women), and for vegetarians and fish eaters the prevalence of obesity was 3% for men and 5% for women, well below the meat-eating group values.

Figure 5.4 summarizes BMI data from the four large published cohort studies of adult vegetarians.19 These studies allow a comparison with non-vegetarian counterparts of the same cohort. Vegetarians in each study on average have 1 to 2 points lower BMI values than meat eaters within the same cohort. This difference is similarly observed in men and women. There is a substantial variation in BMI values among cohorts. USA cohorts have greater BMI than European cohorts. This can be attributed to methodological differences in data collection, geographic location, secular trends, and ethnic or genetic differences. Overall, these epidemiological data clearly suggest that meatless diets are associated with lower overall BMI scores and a low prevalence of obesity in adults.