Control of Energy Expenditure in Humans

Excerpt

Resting and meal-related energy requirements can be assessed by measuring energy expenditure with indirect calorimetry. The indicated method to assess free-living energy expenditure is the doubly labelled water technique. Variation in energy expenditure is mainly a function of body size and composition (resting energy expenditure) and of physical activity (activity energy expenditure). Thus, energy expenditure can be calculated with a prediction equation for resting energy expenditure, based on height, age, weight and sex, in combination with the measurement of the physical activity level of a subject with a doubly labelled water validated accelerometer for movement registration. Energy balance in humans is maintained by adjusting energy intake to energy expenditure. Over- and underfeeding induces changes in activity-induced and maintenance energy expenditure as a function of changes in body weight and body composition. Additionally, underfeeding causes a metabolic adaptation as reflected in a reduction of maintenance energy expenditure below predicted values and defined as adaptive thermogenesis. When intake exceeds energy requirements, the excess is primarily stored as body fat. As a substrate for energy metabolism, fat is less likely to be oxidized for fuel than carbohydrate or protein. Consumed fat is mostly stored before oxidation, especially in heavier people, increasing the likelihood of creating a positive energy balance. An activity-induced increase in energy requirement is typically followed by an increase in energy intake, whereas a reduction in physical activity does not result in an equivalent reduction of energy intake. Thus, preventing weight gain is more effectively reached by eating less than by moving more. For complete coverage of all related areas of Endocrinology, please visit our on-line FREE web-text, WWW.ENDOTEXT.ORG.