Components of energy balance

•Energy intake

•The caloric or energy content of food as provided by the major sources of dietary energy: carbohydrate, protein, fat and alcohol.

•Energy storage

•The energy that is consumed in the form of food or drinks can either be stored in the body in the form of fat (the major energy store), glycogen short-term energy/carbohydrate reserves) or protein (rarely used by the body for energy) or be used by the body to fuel energy-requiring events.

•Energy expenditure

•The energy that is required by the body for metabolic, cellular and mechanical work.

•Calorimetry is the measurement of the body’s energy expenditure

•Direct Calorimetry

•Direct calorimeters have been designed for measuring total heat production in the body,

•but this approach is technically demanding, especially in human studies, and is now infrequently used.

•Indirect calorimetry measures energy production via respiratory gas analysis.

•This approach is based on measuring oxygen consumption and carbon dioxide production that occurs during the combustion (or oxidation) of protein, carbohydrate, fat and alcohol, as shown in the example of glucose combustion.

•Estimations of energy expenditure by indirect calorimetry have been shown to be practically identical to those derived from direct calorimetry.