Protein is made up of long chains of amino acids and is essential for building, maintaining, and repairing cells. The human body needs 20 different amino acids, 12 of which can be produced internally while 8 must come from diet. Amino acids combine to form proteins that serve important functions throughout the body. Most Western diets provide sufficient protein, getting 45-55g per day, though some regions experience protein deficiency diseases like kwashiorkor due to lack of protein in their diets.