To describe characteristics of self-identified popular diet followers and compare mean BMI across these diets, stratified by time following diet.

Cross-sectional, web-based survey administered in 2015.

Non-localised, international survey.

Self-selected followers of popular diets (n 9019) were recruited to the survey via social media and email announcements by diet community leaders, categorised into eight major diet groups.

General linear models were used to compare mean BMI among (1) short-term (<1 year) and long-term (≥1 year) followers within diet groups and (2) those identifying as ‘try to eat healthy’ (TTEH) to all other diet groups, stratified by time following the specific diet. Participants were 82 % female, 93 % White and 96 % non-Hispanic. Geometric mean BMI was lower (P < 0·05 for all) among longer-term followers (≥1 year) of whole food, plant-based (WFPB), vegan, whole food and low-carb diets compared with shorter-term followers. Among those following their diet for 1–5 years (n 4067), geometric mean BMI (kg/m2) were lower (P < 0·05 for all) for all groups compared with TTEH (26·4 kg/m2): WFPB (23·2 kg/m2), vegan (23·5 kg/m2), Paleo (24·6 kg/m2), vegetarian (25·0 kg/m2), whole food (24·6 kg/m2), Weston A. Price (23·5 kg/m2) and low-carb (24·7 kg/m2).

Our findings suggest that BMI is lower among individuals who made active decisions to adhere to a specific diet, particularly more plant-based diets and/or diets limiting highly processed foods, compared with those who simply TTEH. BMI is also lower among individuals who follow intentional eating plans for longer time periods.