The measurement of energy expenditure by the body. Direct calorimetry is the measurement of heat output from the body, as an index of energy expenditure, and hence requirements.
The measurement of heat energy liberated or absorbed in metabolic processes.
The measurement of heat change in a person or system.
The measurement of heat produced by the body or by food.
Measurement of the amount of heat energy produced by an individual. Calorimetry is used by dieticians to determine the energy needs of people who are very ill. It can be conducted either directly or indirectly. Direct calorimetry involves putting a person in a device called a calorimeter and measuring how much heat he or she gives off. This method is expensive and impractical, so indirect calorimetry is usually preferred. Indirect calorimetry uses a device that measures oxygen consumption and carbon dioxide production to calculate energy expenditure and respiration rate. This calculation is used to devise a nutrition care plan for critically ill patients (for example, those who require mechanical ventilation).
The quantification of the energy content in food or an individual’s energy expenditure is achieved through the measurement of calories. Direct calorimetry involves the combustion of a small portion of food within a sealed container immersed in water. The resulting increase in water temperature is utilized to determine the calorie value.
Energy generation in humans can be assessed through the measurement of oxygen consumption. Each liter of oxygen consumed by the body produces approximately 4.8 kilocalories of energy. The level of energy production is determined by comparing the proportion of inhaled and exhaled oxygen in the air.