Metabolic Rate refers to the amount of energy that a body uses in a single day. It is measured in kilocalories and expressed as kcal/day. The amount varies greatly per person because it depends on height, weight, gender, age and level of physical activity. Studies by Spennewyn in 1990 indicated that the amount of lean body mass can be directly correlated to the Metabolic Rate. It is considered medically desirable to have less body fat and more muscle and this is reflected in an increased Metabolic Rate.