In 1993, Dr. Graeme Clugston of WHO presented a rationale for using a value of 2,100 kcal (8.8 MJ) rather than the benchmark value of 1,900 kcal (Clugston, 1993). The increase of 200 kcal (837 kJ) per day was accounted for largely by (1) an increase in the activity increment to 55 percent above BMR (from 40 percent), assuming that a physical activity level (PAL) of 1.4 was incompatible with long-term health; (2) some adjustments to the population's composition; and (3) an increase in the proportion of pregnant and lactating women in the population. While 200 kcal per day represents only a 10 to 11 percent increase, it has significant implications for the amount of food required to support food aid programs.
As will also be evident in this report, the major variable influencing estimates of the mean energy “requirement” for planning purposes is the activity increment. It is difficult, and in many cases impossible, to initially establish the activity level of a population. Therefore, not surprisingly, the various estimates of the mean per capita requirement are not well supported by detailed studies. This acknowledgment reinforces the need to develop and rapidly apply a standardized protocol to monitor physical activity levels in order to refine initial estimates of food needs.
The underlying assumptions and the methods available for estimating the energy needs of individuals, classes of people, and of populations are described in the FAO/WHO/UNU report, “Energy and Protein Requirements ” (1985). As defined in that report:
the energy requirement of an individual is the level of energy intake from food that will balance energy expenditure when the individual has a size and body composition, and level of physical activity, consistent with long-term good health; and that will allow for the maintenance of economically necessary and socially desirable physical activity. In children and pregnant or lactating women the energy requirement includes the energy needs associated with the deposition of tissues or the secretion of milk at rates consistent with good health (p. 12).
There is only one level of intake that balances the energy requirement of an individual. If energy intake is below this requirement, there will be a reduction in body weight and fat, and in lean body mass and activity if the deficit is sufficiently severe or prolonged. If intake is more than required, the individual will gain primarily fat. When sufficient food energy is available, physiological mechanisms control appetite so that individuals can regulate their intake to maintain energy balance. While energy balance and health can be maintained over a range of body weights for the same individual, severe or prolonged weight loss