carbohydrate molecules

Human action is an expression of biological energy derived from food. Living cells are glucose-burning machines. Animals take advantage of the ability of plants to manufacture sugar and other nutrients. The energy, which supports us, is locked into the molecular bonds of a few basic fuel molecules: glucose, fructose, fatty acids, and amino acids. The 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; amino acids may be utilized as energy when glucose intake is limited or glucose utilization is impaired as in diabetes.