Metabolic balance studies have been used at least since the 1920s. A thorough accounting of calcium balance methodology was reported in 1945 by a group of authors that included Fuller Albright for whom the highest award given by the American Society for Born and Mineral Research.
Balance studies calculate net retention as intake minus excretion. The technique is applicable only when a stable component is under study or when end products of metabolism are clearly recognized.
For example heat is the end product of energy metabolism and all forms of energy may be expressed as heat. Therefore the balance experiment may be used in studies of energy exchange.
Protein balance is determined by measurement of its metabolically stable component, nitrogen. Balance studies should be performed for several days on a constant protein intake in steady-state conditions.
Mineral elements are stable substances and therefore led to themselves to the balance technique.