Your organism needs protein!
Many nutritionists believe that people should consume proteins with different structures a few hours apart to be able to synthesize useful proteins from them. This is especially important for vegetarians, since protein found in vegan food does not contain all necessary amino acids.
Foods that contain a sufficient amount of all essential amino acids are an important part of a nutritious and well-balanced menu. Usually these are animal products. Some fruits and vegetables, cereals and beans can provide people with non-essential protein. Such vegetable products can still be an excellent source of protein if they're chosen to supplement one another. Then your body gets all the necessary amino acids. Good supplementary sources of protein include corn, beans, bread, and nuts.