|Activity, Energy Expenditure and Energy Requirements of Infants and Children (International Dietary Energy Consultative Group - IDECG, 1989, 412 pages)|
(Discussion leader J.C. WATERLOW, rapporteur A.A. JACKSON)
Waterlow stated that although his assignment included consideration of both the prevention and treatment of protein-energy malnutrition, his introductory comments would only focus upon prevention. He pointed out that there was general agreement that the condition represented a multiple deficiency state in which the interaction with infection was very important. He drew attention to models of the disease in which the effects of dietary imbalances might be expressed through a final common pathway. He suggested four points for consideration as far as prevention is concerned:
1. If estimates of energy requirements for children were to be reduced, what would be the impact upon our ideas about requirements of other nutrients, and the ability of the diet to satisfy these requirements? The P:E ratio in breast milk was used as an example.
2. It would appear that there may be only a narrow zone which separates an adequate from an inadequate intake. The ability of an individual to adapt across this zone has not been discussed to any extent. It is not clear how strong the evidence is for adaptation.
3. Does the new knowledge help us to understand why some children become malnourished but others do not? To what extent are interindividual differences of importance?
4. For public health purposes there is a need for guidelines which can be used for adjusting to situations in which there is a high morbidity. There is a need for general practical guidelines which can be used as a 'rule of thumb'.
Addressing the first of these issues, Jackson noted that if reducing the total intake were to give rise to a marginal deficiency of specific nutrients, and deficiency of a specific nutrient were to give rise to a wastage of energy, then a self-correcting situation would be created. A reduction in energy intake, and hence a reduction in total food intake, would give rise to a specific nutrient deficiency; this would cause energy to be wasted, thereby requiring an increase in energy intake to match the increased expenditure. The increase in energy intake, and hence total food intake, would serve to correct the inadequate intake of the limiting nutrient.
Lucas noted that if the energy requirement were less than had been thought and the requirement for protein were unchanged, this would imply an increase in the P:E ratio required by the infant. For modern infant formulas the P:E ratio is already greater than the theoretical ratio; and there is some evidence that it is inappropriately high.
There is no reason to believe that by reducing the total energy intake there would be any increased risk relating to the adequacy of essential fatty acid intake.
Prentice raised the question as to why we should want to decrease the RDA for energy in infants. Waterlow pointed out the importance of these estimates for assessing the adequacy of the intakes of children in the Third World. As all the data using doubly-labelled water (DLW) imply relatively lower figures than before, this is of practical importance. Choto said that, bearing in mind the extent of interindividual variability, there was a need to exercise caution in proposing a lower requirement for everyone. A more appropriate approach might be to define a minimum level of energy in association with a minimum level of protein, all other nutrients being adequate. Dewey argued that there was a need to define several levels: a minimal level of intake, a level of intake which was safe for planning diets, and an upper safe or maximal level of intake. Valyasevi emphasized the different purposes for which recommendations might be used, and the specific problems faced by transitional societies with a mix of problems of undernutrition and overnutrition. He supported the concept of an acceptable range with an upper and lower limit.
It was emphasised by a number of speakers that the minimal level should not represent a level at which there was any risk of a sacrifice of function. It was unlikely that the minimal level would be the same as the maintenance requirement, or the lower end of the distribution curve for intakes. Weisell pointed out that in the past there had been theoretical discussions of the relative merits of the alternate approaches, and a minimum had been rejected in favour of the average. Thus, a move towards a range would be against the thinking of nine years earlier.
Waterlow indicated that consistency would also mean that requirements be based upon figures for expenditure, i.e., using DLW, rather than upon measurements of intake, in response to a question from Ferro-Luzzi who noted that the recommendation of the 1985 Committee was an intake 5% above the actual intake, with 5% for desirable activity and 5% to cover uncertainty about the composition of the intake. Torun noted that, for diets containing a moderate amount of fibre, an additional 2.5 to 5% should be added. There was general agreement that more information was required on the conversion of gross to metabolisable energy of different diets.
There was some discussion on the basis of interindividual variability, and the extent to which this might be accounted for by behavioural components. Prentice said that they had attempted to look prospectively at total energy expenditure (TEE) and growth performance, but had not been able to show any direct relationship. Super suggested that one should not simply consider the net rate of growth, but recognize that behaviour, as a response, included the interaction with the environment. Dewey felt that the highest rates of growth would, by definition, be achieved by those with the highest intakes. Waterlow pointed out that, were this true, it would not allow for variation in the efficiency of utilisation of food. Butte noted that in their early studies there was no good relation between energy intake and weight gain. Over the longer term there was a relationship between energy intake and weight gain, but not between energy intake and energy expenditure.
Pollitt noted that the identification or classification of categories of activity in the 1985 report was based upon adult considerations and was really inappropriate for children. There was the need to identify categories of activity of relevance to infants and children.
Dewey raised the question as to how the apparent differences in energy expenditure between breast-fed and bottle-fed infants should be interpreted. Butte indicated that the data were not entirely clear on this point with different series of children giving somewhat different results. It was not clear to what extent changes in the thermal environment might modify the results, or limit the extrapolation of experimental findings to the free-living situation.
It was recognized that there were very few data available on children between 3 and 10 years of age. A number of studies are in progress which should help to fill this gap in knowledge.