Energy Balance

Abstract

Energy balance in animals and man is a balance between energy intake and energy expenditure for body functions and physical activity. Energy expenditure determines energy requirement. Energy requirement is met by energy intake. When energy intake does not match energy requirement, there is a misbalance, caused by intake that is either too high or too low. When intake exceeds expenditure, there is a positive energy balance and excess energy is stored in body reserves. When energy intake does not meet expenditure, energy is mobilized from body reserves. Both result in a change of body weight and body composition. This chapter firstly describes the assessment of energy expenditure in man, based on the methodology as described for animals in the foregoing chapter. Subsequent sections describe assessment of physical activity, food intake and body composition, resulting in the assessment of energy and macronutrient balance. The methodology forms the basis for the insights as described in the following chapters on regulation of energy balance as a function of behaviour, growth, disease, and ageing. Energy balance can be derived from the measurement of energy expenditure, food intake, and body composition. The indicated method for the measurement of energy expenditure is indirect calorimetry via a ventilated hood, respiration chamber and with the doubly labelled water method. Food intake is usually assessed with self-report like a dietary recall or a dietary record. Self reported food intake has important limitations and the validity is insufficient for research purposes. Body composition can be calculated from body weight and body volume or total body water. At a negative or positive energy balance, the deficit or excess energy is largely mobilised or stored as body fat. The best long term indicator for energy balance over weeks and months is body weight and body composition. With the present state of the art, disturbances of energy balance are better determined by measuring energy expenditure than with measuring food intake.