A recent meta-analyses of twelve randomized controlled trials, involving a total of 1151 subjects evaluated the effect of a vegetarian diet on weight loss.
Overall, individuals assigned to the vegetarian diet groups (intervention of median 18 weeks) lost significantly more weight than those assigned to the non-vegetarian diet groups: -2.02 kg (95%CI: -2.80 to -1.23).
Subgroup analysis detected significant weight reduction in subjects consuming a vegan diet (-2.52 kg; 95 % CI: -3.02 to -1.98) and, to a lesser extent, in those given lacto-ovo-vegetarian diets (-1.48 kg; 95 % CI: -3.43 to 0.47).
Vegetarian diets appeared to have significant benefits on weight reduction compared to non-vegetarian diets. The reasons for the greater weight loss among vegans and to a lesser extent lacto-ovo vegetarians diets aren’t clear. Possibly, it is because these diets are more restrictive.