A vegetarian diet will result in a quicker weight loss because it tends to be low in calories. “You may loose weight but you also may lack energy,” says Frechman. You’ll get more vitamins, minerals and nutrients but you probably won’t get enough calcium (from diary) or essential fatty acids (from fish) or folic acid (from grains). Also noticeably absent from most vegetarian menus: Protein, which protects your immune system and builds muscle mass. “If you’re on a vegetarian diet long enough, you could suffer from malnutrition.”