ABSTRACT
The body is about 40% efficient in capturing the energy from the catabolism of the energy-yielding nutrients. Energy can be released by the cell both aerobically and anaerobically. Creatine phosphate, a high-energy compound, serves as an energy reservoir for the body. Direct and indirect calorimetry are used to determine the amount of energy being expended by the body. Generally human energy expenditure is measured by indirect calorimetry in which oxygen utilization is measured either as oxygen consumption or carbon dioxide production or both. The three components of human energy expenditure are basal metabolism, thermic effect of food (also known as specific dynamic effect, specific dynamic action, and diet-induced thermogenesis), and thermic effect of exercise (also known as physical activity). Energy is expended during the digestion, absorption, and metabolism of nutrients. This diet-induced thermogenesis reaches a maximum within about an hour after a meal. The thermic effect of food usually accounts for 6 to 10% of the total energy expenditure.
