Beans are a very good source of protein and fibers, for example, black beans. These are considered in both vegetable and protein food groups. Proteins are found in less quantity in vegetable so for people who are vegetarian beans are the best source to gains protein.
Apart from protein they also contain many vitamins and minerals that are required by the body. Eating black beans regularly on an adequate amount helps in maintaining healthy bones, healthy digestion, lowering blood pressure and provide several other help benefits. So the correct answer is black bean.
