|Activity, Energy Expenditure and Energy Requirements of Infants and Children (International Dietary Energy Consultative Group - IDECG, 1989, 412 pages)|
|The energy requirements of growth and catch-up growth|
|2. Outcome variables|
In practice, a number of outcome variables have been used to define the interaction of nutrient intake with growth, and each has its relative merits.
Following the introduction of systems for the classification of malnutrition which differentiate between stunting and wasting (WATERLOW, 1973), and the increased appreciation that stunting of itself may be associated with long-term functional impairment (GRANTHAM-McGREGOR, POWELL and WALKER, 1989), there has been increased interest in factors that determine and control the achievement of height potential (see WATERLOW, 1987). Attempts to explore the relationship on a community-wide basis have produced some insights, but have not provided us with the ability to focus intervention specifically (GOLDEN, 1985; KELLER, 1987; GRANTHAM-McGREGOR et al., 1989). Similarly, specific associations have not been identified in analyses of the extent to which children recovering from severe malnutrition are able to catch up in height (ASHWORTH, 1975; WALKER and GOLDEN, 1988). Therefore, there are important factors operating of which we have little understanding at the present. There are models of producing substantial height with consistency and reliability that might be worthy of exploration: following the use of human growth hormone in children of short stature; in children with sickle cell disease following splenectomy for hypersplenism (EMOND, 1987); and following the treatment of severe trichuriasis (COOPER and BUNDY, 1988). One important feature of each of these conditions is that not only may the children experience substantial gains in height, but the height gain appears to be of high priority, if necessary at the expense of depositing adipose or lean tissue.
Biochemical and functional tests are of great importance in defining the quality of growth, and detailed consideration of some of these factors is provided by other speakers at this meeting.
The most widely used approach to assessing growth is by the measurement of body weight, to the point where growth is often used casually as a synonym for changes in weight. The great advantages of using body weight are that the measurements are non-invasive and that they are relatively easy to take accurately and reliably. The progressive changes in weight are sufficiently large for a consistent pattern of change to be identified over a period of days to weeks. The major disadvantage of the use of weight is that major alterations in weight may be a consequence of changes in water, lean or adipose tissue content. Growth is generally perceived as a net increase in energy content, with the energy in the form of functionally active, lean tissue. The most usual way of attempting to attribute the increase in weight to an increase in lean tissue is by measurement of nitrogen balance. Hence a substantial literature on growth associates a net increase in the energy content of the body with a net increase in the nitrogen content of the body.