|Activity, Energy Expenditure and Energy Requirements of Infants and Children (International Dietary Energy Consultative Group - IDECG, 1989, 412 pages)|
|Energy cost of communicable diseases in infancy and childhood|
The severity of the caloric deficit is related to the duration and magnitude of the malabsorption and rarely poses a major threat to nutrition unless the deficit is chronic or recurrent. The net effect of the changes with infection that I have reviewed is to increase their need for both dietary protein and energy if satisfactory recovery is to be promoted. Is it possible to be more quantitative?
POWANDA (1977) has summarized data from a wide variety of acute infectious diseases by adding the total nitrogen losses and dividing them by the number of days over which these losses occurred. For all infections the average loss of 0.6 g of protein per kg per day is equal to the mean estimated protein requirement for adults. Diseases associated with diarrhea or dysentery produced an average loss of 0.9 g of protein per kg per day. Higher losses were observed with typhoid fever and other severe infections, reaching 1.2 g of protein per kg per day. If the energy cost of depositing a gram of protein is taken to be 25 kcal (100 kJ), these protein losses would deplete the infected individual by an average of 7 to nearly 30 kcal per kg of body weight (UNU, 1979). Elsewhere in this volume, JACKSON (1990) gives 4 kcal for the latter, but this figure must be corrected for only 90% utilization of dietary energy.
The difficulty with such calculations is that they do not include energy expended for the multiple anabolic responses to the infection. As emphasized earlier, balance studies during recovery indicate these to be substantial, although there are 'savings' of dietary energy during the acute phase of an infection that are due to anorexia. This loss must be made up during the recovery period in addition to the losses due to the deficits arising from malabsorption and that due to infection-stimulated catabolism. Thus, with each infectious episode there is a small decrease in de facto requirement at the time of the infection and a modest increase in energy requirement during the convalescent period. The more severe and closely spaced the episodes of infection, the more likely that full recovery will not occur and that the adverse effects will become cumulative.
Both metabolic and field observations suggest that, even with an optimum diet, it may take two to three times longer to replete than to deplete an individual. In this case, any figure for daily increment of additional energy during recovery only need to be from one-half to one-third of the daily loss during the acute phase of an infection. Of course, if the diet is not sufficient for a maximum rate of recovery, the increments available for recovery are correspondingly reduced and the time required for complete recovery greatly increased. Under developing country conditions there is then a high risk that another episode of infection will occur before recovery has taken place.