Greater weight loss was reported in studies with higher baseline weights , smaller proportions of female participants , older participants , or longer duration s , and in studies in which weight loss was a goal .
The prescription of vegetarian diets  reduces mean body weight , suggesting potential value for prevention and management of weight-related conditions
In observational studies , vegetarians generally have lower body weights compared with omnivores .
However , weight changes that occur when vegetarian diets are prescribed have not been well quantified .
We estimated the effect on body weight when vegetarian diets are prescribed .
Diet and body mass index in 38 000 EPIC-Oxford meat-eaters, fish-eaters, vegetarians and vegans
OBJECTIVE : To compare body mass index ( BMI ) in four diet groups ( meat-eaters , fish-eaters , vegetarians and vegans ) in the Oxford cohort of the European Prospect i ve Investigation into Cancer and Nutrition ( EPIC-Oxford ) and to investigate lifestyle and dietary factors associated with any observed differences . DESIGN : Cross-sectional analysis of self-reported dietary , anthropometric and lifestyle data . PARTICIPANTS : A total of 37 875 healthy men and women aged 20–97 y participating in EPIC-Oxford . RESULTS : Age-adjusted mean BMI was significantly different between the four diet groups , being highest in the meat-eaters ( 24.41 kg/m2 in men , 23.52 kg/m2 in women ) and lowest in the vegans ( 22.49 kg/m2 in men , 21.98 kg/m2 in women ) . Fish-eaters and vegetarians had similar , intermediate mean BMI . Differences in lifestyle factors including smoking , physical activity and education level accounted for less than 5 % of the difference in mean age-adjusted BMI between meat-eaters and vegans , whereas differences in macronutrient intake accounted for about half of the difference . High protein ( as percent energy ) and low fibre intakes were the dietary factors most strongly and consistently associated with increasing BMI both between and within the diet groups . CONCLUSIONS : Fish-eaters , vegetarians and especially vegans had lower BMI than meat-eaters . Differences in macronutrient intakes accounted for about half the difference in mean BMI between vegans and meat-eaters . High protein and low fibre intakes were the factors most strongly associated with increasing BMI
Greater weight loss was reported in studies with higher baseline weights , smaller proportions of female participants , older participants , or longer duration s , and in studies in which weight loss was a goal .
The prescription of vegetarian diets  reduces mean body weight , suggesting potential value for prevention and management of weight-related conditions
In observational studies , vegetarians generally have lower body weights compared with omnivores .
However , weight changes that occur when vegetarian diets are prescribed have not been well quantified .
We estimated the effect on body weight when vegetarian diets are prescribed .