The researchers hypothesize that participants who abstained from animal products dropped significantly more pounds since plant-based foods include loads of filling fiber and slow-to-digest complex carbs. Though more research is needed to confirm these results, the study authors write, "Vegetarian diets appeared to have significant benefits on weight reduction compared to non-vegetarian diets."
Popularized by the documentary Forks Over Knives, the Ornish diet is a low-fat, plant-based diet plan based on whole grains, vegetables, fruits, and legumes. It's based on a lacto-ovo style of vegetarianism, allowing only egg whites and nonfat dairy products. It's packed with vitamins, fiber, and lots of filling plants to keep you satiated. Some studies have shown it can reverse heart disease and have beneficial effects on other chronic health conditions. (BTW, there is a difference between a vegan diet and a plant-based diet.)