there have been no randomized trials comparing the effectiveness of these five different diets on weight loss. There- fore, the goal of this study was to examine the differences in weight loss among participants randomized to adopt an omnivorous, semi-vegetarian, pesco-vegetarian, vegetarian, or vegan diet. Transitioning to plant-based diets may lead to greater increases in fiber [6–8], with high-fiber diets being associated with lower body weights in epidemiologic studies [9], and greater decreases in dietary fat [6–8], with studies showing that low-fat diets are associated with weight loss [10]. Because of these potential changes in nutrients among groups, we hypoth- esized that differences in weight loss would follow similar pat- terns seen in epidemiologic studies with weight loss being incrementally greater along the plant-based dietary spectrum from omni to semi-veg to pesco-veg to veg to vegan diets. Furthermore, we hypothesized that the vegan group would have significantly greater weight loss compared with the pesco-veg, semi-veg, and omni groups.