Individual variations in energy expenditure and intake.

Introduction Our interest in this subject arises from a desire for information on individual variation in energy requirements, on the proportion of a population needing more and the proportion needing fewer calories than any stated estimate of its average energy requirements. We should like to be able to compare an array of intakes of energy of individuals with a corresponding array of their energy requirements and so to determine what proportion, if any, of the population might be at risk. Variations between individuals are to be expected and are known to exist: for example, wide variations in energy intake between individual adults were found in the prewar surveys of Widdowson (1936) on men and of Widdowson & McCance (1936) on women. Widdowson (1947) also found great variation in the energy intake of children and she discussed possible causes. Rose & Williams (1961) have shown wide variations in the calorie intakes of male students of the same weight and, apparently, similar activity. Nevertheless, lack of knowledge on the precise extent of variation between individuals makes it necessary to use mean requirements, with their obvious limitations, in assessing the adequacy of diets. In discussing this unfortunate necessity, Orr & Leitch ( I 937-8) reminded their readers that requirements ‘are average values so that in practice, especially when individual requirements have to be considered, a margin must be allowed’. Recently, Sukhatme (1961) has drawn attention to the limitations of using average requirements, particularly for assessing inadequate diets or estimating the extent of world food shortage. In the early studies on energy needs it was usual to measure dietary intake, to consider it in relation to the occupation and other characteristics of the individuals concerned and so to arrive at an estimate of need. For example, Greenwood & Thompson (1917-18) considered the energy yield of daily diets and estimates of the cost of certain activities in determining the needs of the ‘average man’ for an ‘average’ day’s work. Another way of tackling the problem is to measure energy expenditure, and attempts have been made to do it by various means. One way is to sum the energy needed for basal metabolism, the extra energy needed for daily activities and an allowance for the specific dynamic action of foods (cf. Orr & Leitch, 1937-8). Another way is to record the time spent by individuals on each and all the separate