They are also used to make soybean oil , tofu , soy sauce , soy milk and soybean flour . Many vegetarians use foods made of soy , as it is rich in protein . Common forms of soy ( or soya ) include soy meal , soy flour , soy milk , tofu , textured vegetable protein ( TVP , which is made into a wide variety of vegetarian foods , some of them intended to imitate meat ) , tempeh , soy lecithin and soybean oil .