Complete proteins, which come from animal sources such as chicken, fish, dairy and soybeans, contain all the essential amino acids that help build your muscle and body tissue. Incomplete proteins, found in plant foods, such as grains, seeds, nuts, beans and vegetables, provide a varying but limited array of amino acids.A greater variety and amount of incomplete proteins must be consumed to cover all the amino acids needed for protein building.roteins are the building blocks that grow and repair your body. Proteins are needed not only for muscle but also for hair, skin and internal organs. Some proteins travel around your body in the blood as hormones, enzymes and red blood cells.