How Is Energy Expenditure Measured?
In the research or hospital setting, energy expenditure is determined by examining inhaled and exhaled air and measuring the person’s oxygen consumption and carbon dioxide production. The ratio between oxygen consumption and carbon dioxide production is called the respiratory quotient or RQ. Daily energy expenditure in kilocalories is calculated from an equation that accounts for the number of units of oxygen and carbon dioxide exchanged by a person under specific conditions. This technique for measuring energy expenditure is called indirect calorimetry because it measures heat production (calories) indirectly from respiratory gas exchange. In the United States, a number of laboratories have built room-sized indirect calorimeters. Volunteers stay in the room for a total of 24 hours. During this time they are served meals and snacks, and they have access to a TV, VCR, telephone, desk, chair, bed/couch, and toilet facilities. While this technique accurately determines energy expenditure,
