There are an increasingly rising number of people who adopt a plant-based diet. The desire for weight control and other health benefits are driving factors behind this dietary preference. The aim of this study was twofold: first, it reviews intervention studies evaluating the impact on body mass index and weight by various plant-based diets. Most of them were randomized controlled trials of overweight, type 2 diabetes mellitus and/or cardiovascular disease participants compared a low-fat vegan diet to an omnivore diet. Second, this study reviews two major dietary processthat may lead to reduced-body fat. Interventional trials have consistently demonstrated that consumption of plant-based diets reduces body fat in overweight and obese subjects, even when controlling for energy intake. Nonetheless, the mechanisms underlying this effect have not been well-defined. Our review indicatesthat in some patient groups, plant-based diets can enhance weight condition. In certain studies, due to fat consumption limits accompanied by decreased energy intake, the results of the various treatments vary depending on the particular plant-based diets studied. Future research should seek to include a representative population of the sample and apply diets without dietary limitations to the study.