Proteins are substances made from combinations of amino acids.
Amino acids are chemical compounds containing nitrogen , carbon, oxygen, and hydrogen in distinct arrangements. Amino acids usually contain sulfur and sometimes phosphorous, iron, or iodine. Proteins can serve as an energy and heat source for the body and are needed for proper elimination of waste materials through urine. Proteins are broken down into amino acids by enzymes in the stomach and small intestine. Amino acids are then transported to the liver and other organs where they are resynthesized into proteins the body can use or burn as fuel.