These elements build up a human body and are largely divided into two groups, body fat and lean body. Lean body is divided to protein, mineral, and body water. Protein is a main element of muscles and mineral is found mostly in bones. Body water consists of intra-cellular and extra-cellular water. Intra-cellular water gives cell volume and extra-cellular water is composed of blood, lymph, etc. Body cell mass is the sum of intra-cellular water and metabolically active tissues.