Average of 16% of adult body is composed of protein. This is not a type of storage, is a type of living cells which have spesific functions. Proteins are split into amino acids and are transported to liver by blood. Then compounding here they compose body tissue proteins. Protein also is used as energy source in the body. Proteins compose main structure of cells. Body tissues and organs are made by compounding specific cells. Protein is the main nutrient that regulates body function for growth and development. In the course of time, many cells die and new ones are synthesised. Main structure of immune systems, enzymes and some of the hormons used in regulation of body functions are proteins.