Proteins are especially necessary for the growth and maintenance of body structures. The bones, skin, and other solid parts of the body are made up largely of proteins. Proteins also provide energy and make up 12 to 15 percent of the diets calories. Animal proteins are found in beans, grains, nuts, and vegetables.

People get seriously ill if they don't get enough proteins. For example, children in Africa suffer from a disease called kwashiorkor, because their food is low with proteins. They grow slowly and have weak antibodies for their resistance to diseases. Some people suffer from a disease called sickle-cell anemia, because their blood cells contain a kind of protein not exactly suited for its job. Blood cells containing such faulty protein frequently collapse causing anemia.