Cross-sectional studies have shown that vegetarians and vegans are leaner than omnivores. Longitudinal data on weight gain in these groups are sparse.
We investigated changes in weight and body mass index (BMI) over a 5-year period in meat-eating, fish-eating, vegetarian, and vegan men and women in the UK.
Self-reported anthropometric, dietary and lifestyle data were collected at baseline in 1994-1999 and at follow-up in 2000-2003; the median duration of follow-up was 5.3 years.
A total of 21,966 men and women participating in Oxford arm of the European Prospective Investigation into Cancer and Nutrition aged 20-69 years at baseline.
The mean annual weight gain was 389 (SD 884) g in men and 398 (SD 892) g in women. The differences between meat-eaters, fish-eaters, vegetarians and vegans in age-adjusted mean BMI at follow-up were similar to those seen at baseline. Multivariable-adjusted mean weight gain was somewhat smaller in vegans (284 g in men and 303 g in women, P<0.05 for both sexes) and fish-eaters (338 g, women only, P<0.001) compared with meat-eaters. Men and women who changed their diet in one or several steps in the direction meat-eater --> fish-eater --> vegetarian --> vegan showed the smallest mean annual weight gain of 242 (95% CI 133-351) and 301 (95% CI 238-365) g, respectively.
During 5 years follow-up, the mean annual weight gain in a health-conscious cohort in the UK was approximately 400 g. Small differences in weight gain were observed between meat-eaters, fish-eaters, vegetarians and vegans. Lowest weight gain was seen among those who, during follow-up, had changed to a diet containing fewer animal food.