Energy Requirements

Written by Doctor Admin Friday, 19 March 2010 17:39

It  is popular for governments and international agencies to prescribe recommended dietary allowances for most nutrients. These may be based on normal intakes of a healthy population or on experimentally determined physiological minima plus some safety factor. In the case of energy, there is a very real dilemma because of the wide range of energy utilization, and all committees so far have only stated average requirements for group of individuals.

Unfortunately, this can only be of limited value, because it is impossible to ascertain whether food is distributed according to the physiological requirements of individuals. For example, it is often important to estimate the number of undernourished individuals in a population to ascertain the seriousness of a problem, and there is no standard for this calculation on the basis of food consumption. This is no ivory tower exercise, because undernutrition is almost certainly the most serious nutritional problem in the world today, and it is important to quantify it on humanitarian grounds and for logistic reasons. It is also politically important.

From what is now known about adaptations to high and low caloric intakes, it would seem that there is a range over which energy expenditure may be adjusted to ensure energy balance. Below this range there will be an inevitable loss of body substance, and above it, fat will accumulate. The range for normal individuals is quite wide, but  it may depend upon genetic factors.

Future committees migh be more useful if they were to estimate the range. For instance, the might decide that it was injurious to health for a man to consume less than 1,500 kcal/day or more than 3,000 kcal/day. Such a recommendation would have far reaching effects, because it would remove much of the world food problem and direct aid to the really needy.

Later committees might feel that 3,000 kcal/day is too high a maximum, because there is a low prevalence of diseases of civilization among populations where few individuals consume more than 2,500 kcal/day. Adaptation to low intakes are known to increase longevity, adaptation to high intakes may carry a penalty.