If you are designing such a formula, you have to decide what fuels you are going to add to supply energy. Living cells are glucose-burning machines. Animals take advantage of the ability of plants to manufacture sugar and other nutrients. This energy is released as the energy-supplying molecules are dismantled by oxidation. Food-derived energy allows us to move, to do work by muscle contraction, and to keep warm.
Body heat is generated by the metabolic activity of every cell.
Carbohydrates and fats are the principle sources of energy , although amino acids may be utilized as energy. Combustion of amino acids requires the excretion of nitrogen, which is first converted to ammonia. Glutamine is the shuttle which carries ammonia from rapidly-metabolizing tissues to the liver. The liver converts ammonia to urea , which is delivered to the kidneys for excretion in the urine. The energy requirement of any individual is determined by physical activity.