Nutritional adaptation and variability

In current nutrition literature man's requirement for energy for a given status and pattern of physical activity and body mass is fixed. Available experimental data on the other hand show that it is variable and self-regulated over a considerable range. This homoeostatic range is associated with covariance of man's genotype with local environmental effect under a sustained perturbation of common external environment. The implication is that man can have his intake anywhere in the range without being under nutritional stress. Below the lower limit of this range man is under energy stress, growth is retarded and man adapts to small body size. Unlike the homoeostatic range, this long-term adaptation is heritable, but there is no evidence that work output equals energy intake in adaptation to low intake. On the contrary, small subjects on a lower plane of nutrition are found to be metabolically more efficient. Evidence is cited to show that it is the decrease in BMR in subjects with low intake which plays a major role in facilitating a higher level of metabolic efficiency for subjects undergoing energy stress.