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Implications of new knowledge for recommendations of energy intakes

(Discussion leader A. LUCAS, rapporteur B. SCHÜRCH)

Requirements can be derived from (1) the sum of individual components of energy expenditure, (2) the dietary intake of children growing normally, or (3) energy intakes associated with optimal health. Longitudinal studies are now underway to obtain data of the third kind, which should provide the best answer. In the meantime, however, we have to decide whether or not to recommend changes of requirements based on results of recent doubly-labelled water studies. Complicating the decision are factors such as secular trends in growth performance which raise questions as to what growth rates to accept as a standard; possible cultural differences in energy needs; and the great intra-individual variation in energy needs, e.g., for catch-up growth.

Most discussants agree that, at least for the first 3 months, exclusive breast-feeding should be recommended under most circumstances. Recommended energy intakes from breast milk cannot be specified, and, it therefore makes sense, at least for the time being, to base recommendations of energy intakes during the first 3 months post partum on the energy intakes of breast-fed infants. This leaves us with the methodological problems of how best to assess the energy intakes of breast-fed infants (test-weighing and milk sampling, breast-shield, or doubly-labelled water method).

In older children, assessments of energy intakes can vary by up to 20% depending on how one measures dietary intake, how one calculates the energy content of the diet, and how one takes into account such factors as fecal losses, non-digestible polysaccharides, etc. The energy source too may be important, if we consider outcomes such as morbidity. Little is known about the extent to which intakes determine expenditure and/or expenditure determines intakes. A French study showed that upper-class children have lower energy intakes than lower-class children, yet upper-class children watch less TV.

Problems like these make it seem safer to base estimates of requirements on what appear to be desirable expenditure levels. This, however, means that we need a considerable amount of information on how children spend their time and energy. Should we then go one step further and stipulate how much energy children should expend? In theory yes, but in practice we may not be able to have much influence on children's activity patterns. We may, therefore, run smaller risks in making recommendations based on their current habitual activity patterns, provided they are not excessively sedentary (e.g., spending hours watching television every day).

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