Proteins are used for the growth and maintenance of body tissues and for the production of substances such as hormones and enzymes which help to control many functions within the body.   If insufficient carbohydrate and fat are available in the diet, then protein may also be used to provide the body with energy.  Proteins are made from building blocks known as amino acids.  There are 20 different amino acids.  Of the twenty, eleven amino acids can be made in the body while the other nine can only be supplied by the diet.  These nine are known as the essential amino acids.

Some foods are better providers of these amino acids than others.  All of the amino acids are found in meats and dairy foods.   Fewer of the amino acids are found in plant foods such as cereals, beans, lentils, and nuts.  However, a wide variety of protein sources in the correct amounts can work together to provide the ideal levels of the different amino acids.