Since at least the mid-1980’s, scientists have found that vegetarians and vegans tend to weigh less than omnivores (meat-eaters). Decades later, whether adopting a vegetarian diet can lead directly to weight loss is still under scrutiny.
Population Studies
A vegetarian diet is associated with low body weight and low body fat.
1. In the UK, body mass index (BMI, a ratio of weight to height) and as estimate of fatness) was 36% lower in males and 31% lower in females following a vegetarian diet compared to meat-eaters, even after taking into account other dietary variables like fibre, smoking, and alcohol (Appelby et al. 1998).
2. A Swedish study found that those who avoid red meat (but eat poultry), lacto-vegetarians (dairy-consuming vegetarians) and vegans have a lower risk of being overweight or obese than omnivores.
Forty percent (40%) of red meat-eaters had a BMI above 25; they were overweight. Only 29% of non-red meat eaters and vegans were above the cut-off, and only 25% of lacto-vegetarians were overweight (Newby et al. 2005).
3. A study of vegetarian preschoolers found they were less likely to be obese than their non-vegetarian schoolmates (Dwyer et al. 1980).
4. Among college students, a vegetarian diet is maintained longer than a weight-loss diet (Smith et al. 2000).
The Bottom Line: Long-term maintenance of a meat-free diet might be the key to low body weight (Key & Davey, 1996).
Can Switching to a Vegetarian Diet Cause Weight Loss?
1. As new vegetarians transitioned from an omnivorous diet over six months, they decreased their caloric (energy) intake and increased their carbohydrate intake.
- They had no changes in body weight, but body fat did decrease, and these vegetarians tended to follow dietary recommendations (concerning fat, calories etc.) more closely (Phillips et al. 2004).
2. When 21 966 health-conscious men and women were followed for about five years, vegans and fish-eating women gained the least weight.
- People who switched from being a meat-eater to fish-eater, from fish-eater to vegetarian, or from vegetarian to vegan gained the least amount of weight (242 grams for men, 301 grams for women)
- Differences between all groups were small but the smallest weights gains were among those who decreased their consumption of animal products (Rosell et al. 2006).
The Bottom Line
- Vegetarians and vegans are less likely to be overweight and obese than those who eat meat.
- It is still unclear whether switching from to a vegetarian diet will necessarily cause weight loss; but the evidence is building;
- Cutting out red meat is associated with lower body weight;
- Switching to a vegetarian diet can lead to small weight losses, and these losses become more significant over time;
- Experts recommend going vegetarian - or at least increasing plant foods and eating fewer animal products – to help weight control (Newby et al. 2005).
References:
Appelby M, Mann JI, and Key TJ. Low body mass index in non-meat eaters: the possible roles of animal fat, dietary fibre and alcohol. International Journal of Obesity and Related Metabolic Disorders. 1998; 22(5):454-60.
Dwyer JT, Andrew EW, Valadian I, and Reed RB. Size, obesity, and leanness in vegetarian preschool children. Journal of the American Dietetic Association. 1980; 77(4):434-9.
Key T and Davey G. Letters: Prevalence of obesity is low in people who do not eat meat. BMJ. 1996; 313:816-17.
Newby PK, Tucker KL, and Wolk A. Risk of overweight and obesity among semivegetarian, lactovegetarian, and vegan women. American Journal of Clinical Nutrition. 2005; 81:1267-74.
Phillips F, Hackett AF, Stratton G, and Billington D .Effect of changing to a self-selected vegetarian diet on anthropometric measurements in UK adults. Journal of Human Nutrition and Dietetics. 2004; 17(3):249-55.
Rosell M, Appleby P, Spencer E, and Key T. Weight gain over 5 years in 21 966 meat-eating, fish-eating, vegetarian, and vegan men and women in EPIC-Oxford. International Journal of Obesity. 2006; 30(9):1389-96.
Smith CF, Burke LE, and Wing RR. Vegetarian and weight-loss diets among young adults. Obesity Research. 2000; 8(2):123-9.
