BODY COMPOSITION. The term body composition describes the various components that make up a person's body. The absolute and relative amounts and distribution of these components are relevant to diverse body functions and, thus, influence the state of health and various disease risks. A commonly used body composition model organizes the body to five levels of increasing complexity: from atomic to molecular, cellular, tissue-system, and whole body.

At the atomic level, the body is made up of chemical elements essential for life. Four major elements, oxygen, carbon, hydrogen, and nitrogen, collectively account for more than 96 percent of adult body weight. The remaining are minerals present in the form of salts. Calcium and phosphorus make up the major bulk of remaining minerals, found mostly in bone.

The four elements, oxygen, carbon, hydrogen, and nitrogen, are present at the molecular level in water and as organic...