Macronutrients comprise carbohydrates, fats and proteins and make up most of the body's soft tissue structure. Carbohydrates are organic molecules made of carbon, hydrogen and oxygen atoms. Fats are composed of carbon, hydrogen and oxygen, but the proportion of oxygen atoms to carbon and hydrogen is lower than in carbohydrates. Proteins are usually made up of more than 100 amino acids linked into chains by peptide bonds. Amino acids consist of an asymmetrical carbon atom with both an amino group (NH2) and a carboxyl group (COOH) attached. Energy used for metabolic homeostasis, thermoregulation, physical activity and normal organ function is obtained from the oxidation of these macronutrients. Micronutrients (trace minerals and vitamins) are dietary components necessary to sustain health. Most trace minerals appear to function as cofactors for a number of enzymes. Vitamins have many roles in intermediary metabolism and in the specialized metabolism of specifc organs.