|Activity, Energy Expenditure and Energy Requirements of Infants and Children (IDECG, 1989, 412 p.)|
(Discussion leader P.S. SHETTY, rapporteur A.M. PRENTICE)
The paucity of data on energy expenditure, body composition, activity patterns, metabolic effects of infection and the importance of diet composition for children were reiterated. But do these deficiencies in knowledge inhibit our ability to make or modify recommendations?
The concept of using the doubly-labelled water method as the gold standard on which to base requirements was generally accepted, but with the following caveats: (1) The method still requires more thorough cross-validation in infants and children, and caution was urged until we can be certain that the method is not associated with significant bias. Only when measurements of intake and expenditure can be made to agree, can we be confident in each estimate. (2) Doubly-labelled water (DLW) provides no information on qualitative aspects of activity and expenditure which are essential to making judgements as to whether the energy expenditure is optimal. (3) Since DLW measurements provide an estimate of metabolisable energy there remains the need to translate these estimates into food requirements. The conversion of gross food energy into metabolisable energy was identified as a major area for future research, especially in circumstances where there is a high intake of what has been assumed to be unavailable carbohydrate.
It was recognised that researchers using the DLW method were building up a large data-base which would be highly influential in making future recommendations. The fact that the data obtained so far had not influenced the recent US RDAs was ascribed to the inherent conservatism of the advisory process and should not be interpreted as a rejection of the principle of basing requirements on estimates of expenditure.
The need for more information on body composition in chronically energy-deficient children was stressed. With modern technologies it should be possible to make much more refined measurements of fat, lean and active organ mass. These data are necessary to determine both the consequences of energy deficiency and the appropriate denominator for expression of energy expenditure.
A large body of knowledge continues to be built up on the relation between growth patterns and dietary practices. The major problem we are facing is assessing the long-term outcome of different growth patterns. The need for such long-term outcome studies repeatedly emerged as a high priority.
Research was encouraged into the importance of diet quality and its possible significance in modifying energy requirements. Is it true that a diet deficient in certain micro- or macronutrients may enhance thermogenesis? What is the importance of the fat:carbohydrate ratio in the diet? Does the fatty acid profile matter in terms of energy requirements?
A plea was made for more research into improved methods for assessing food intake since these would continue to be the major source of information from many populations for the foreseeable future in view of the difficulties and costs associated with the DLW method. It was suggested that methods based on urinary measurements of nitrogen be reconsidered.
Several contributors sought to stimulate developments in new ambulatory methods for assessing oxygen consumption, heart rate and activity patterns. It was suggested that IDECG might want to play an active role in this.
Further research on the impact of infections on energy requirements and energy intake was identified as being of high priority. Is the concept of a post-infection anabolic window associated with hyperphagia and catch-up growth in order to reestablish growth along the previous centile a real one? If so, how long does the period last? How can needs be met during this period? What is the maximum rate of catch-up growth to be expected in a village situation? Is repletion during a 5-day period as effective as repletion during a 10-day period?
In summary, the group identified major areas for future research. Many of the issues were not new, but the presentations at this meeting revealed that little progress had been made in several of the most important areas.