Are complex organic compounds that form the main structure of muscles, organs, and glands. -The body is about 20% protein by weight. – Proteins are made up of amino acids, and if they are not present in the right balance, the body’s ability to use protein will be affected. Because protein deficiency affects all organs and is of particular concern during childhood, adequate intake of high-quality protein is essential for health. – Eight of the amino acids are considered essential for adults because they must be obtained from food, and arginine and histidine are also essential amino acids for children.