Final answer:
The use of oxygen consumption or carbon dioxide production to measure an organism's metabolic rate is known as indirect calorimetry.
Step-by-step explanation:
Using oxygen consumption or carbon dioxide production to measure the metabolic rate of an organism is called indirect calorimetry. This method is based on the principle that a specific amount of energy, approximately 20 kJ, is generated for each liter of oxygen consumed during the metabolic process. The measurement of oxygen or carbon dioxide allows us to determine basal metabolic rates (BMR) and can provide useful information about a person's level of fitness or potential medical issues. Oxygen consumption and the rate of energy expenditure are directly proportional because the digestive process is fundamentally about oxidizing food to release energy.