Energy expenditure as the basis for estimating energy requirements

The energy requirement of an individual, in a state of desirable equilibrium, is equal to the energy expenditure. In some clinical situations, where an improvement in nutritional status may be advisable, the energy requirement may be set at a higher level than the energy expenditure in order to produce, temporarily, a positive energy balance. In certain physiological states, such as during growth in children, or in pregnancy and lactation, the energy requirement may also be higher than the energy expenditure. At the other extreme, when dealing with an obese individual or an obese population, again energy requirements would be derived from the energy expenditure, with a reduction to produce a negative energy balance; the amount and the duration of the energy imbalance would determine the rapidity and extent of the weight loss.

A more difficult situation to judge is where the energy requirements might be construed as being inadequate, because energy expenditure was less than desirable due to low levels of physical activity. In the absence of very clear-cut evidence specifically related to the health advantages of physical activity and the clinical dangers of inactivity which, for adults do not presently exist in an uncontroversial and entirely persuasive way - it is problematical to take this factor into account in calculating energy requirements. This is not to say that physical activity may not be important for physical, mental, and cognitive development and maintenance, particularly in children: it simply appears very difficult to introduce it in a quantitative way in the present context.