Activity, Energy Expenditure and Energy Requirements of Infants and Children (International Dietary Energy Consultative Group - IDECG, 1989, 412 pages): Total energy expenditure of free-living infants and children obtained by the doubly-labelled water method: 4. Outstanding methodological concerns

Activity, Energy Expenditure and Energy Requirements of Infants and Children (International Dietary Energy Consultative Group - IDECG, 1989, 412 pages)

Total energy expenditure of free-living infants and children obtained by the doubly-labelled water method

		(introductory text...)
		Abstract
		1. Introduction
		2. Method
		3. A review of published studies
		4. Outstanding methodological concerns
		5. Future studies
		6. Conclusions
		References

4. Outstanding methodological concerns

The very limited amount of cross-validation data in children has been highlighted above. It would be preferable to have much more data in this respect, but in reality it is unlikely to be forthcoming due to the difficulty of obtaining comparator measurements of carbon dioxide production or energy expenditure in young children over long periods. Furthermore, it is difficult to validate a technique which the theoretical estimates of error suggest is likely to be more accurate than any possible 'reference' method.

A specific concern that has arisen from the review of the world literature presented above is that many of the studies are yielding very high coefficients of variation for TEE in any given age group. Examples of these are illustrated in Figure 11 in which all CVs refer to data expressed per kg body weight which should remove a large part of the variance arising from differences in body size. The CVs are commonly in excess of 25% implying that there is a three-fold range in TEE between a child at -2 SD and one at +2 SD. Is this a genuine phenomenon, or is it a result of random errors which are expanding the true range? We have taken two approaches to this question. The first is to re-analyse samples from subjects who yield outlying values and to scrutinise their data with particular vigilance in order to search for a priori grounds for excluding the result. This approach sometimes reveals errors in the analysis or unacceptably high propagated errors, but usually fails to do so. Furthermore, the results presented for publication are calculated after any such exclusions (see Vasquez-Velasquez and Davies data sets in Figure 11). A second way of detecting unacceptably low TEE values is to calculate the ratio TEE/SMR since this would never be expected to be below 1.2. VASQUEZ-VELASQUEZ (1989) and DAVIES (unpublished) have performed such an analysis and found very few results lower than 1.2 x SMR and none below 1.0 x SMR. These results fail to reveal any obvious reason to question the high CVs, but they remain intuitively surprising and require further thought as fresh data sets become available.

Figure 11. Published coefficients of variation for TEE expressed per kg body weight.