|Activity, Energy Expenditure and Energy Requirements of Infants and Children (International Dietary Energy Consultative Group - IDECG, 1989, 412 pages)|
|Energy-sparing mechanisms: reductions in body mass, BMR and activity: their relative importance and priority in undernourished infants and children|
The few observational studies that have been published on the physical activity of young children suggest that a decrease in spontaneous activity is an early result of an inadequate energy intake. In the present state of knowledge, to get information about effects on metabolic rate and body composition we have to go back to the severely malnourished child and follow the changes that occur during recovery.
In severe malnutrition the normal pattern of organs and tissues is distorted; muscle is greatly depleted and brain well preserved; visceral organs occupy an intermediate position. Since the better-preserved organs have a high metabolic rate (MR), there will be a tendency in malnutrition for the MR per kg body weight to be greater than normal, as has indeed often been observed. If the MR per kg is low, this must mean that the specific metabolic rates of active tissues are depressed. It is suggested that the best way of expressing the MR in malnutrition is to relate it to total body potassium (TBK). Unless there is specific K depletion, there should be a close relation between TBK and the amount of intracellular protein in the body. Measurements made on this basis have confirmed that in malnutrition there is a reduction in MR per unit K, which is more severe in children with marasmus than in those with kwashiorkor.
Studies in Jamaica have shown that, as children recover from malnutrition, MR and whole-body protein turnover rise within 10-14 days to levels above normal. These changes are followed by restoration of muscle and fat and renewed skeletal growth.
We do not know whether this sequence of events occurs in the reverse order in the child who is becoming malnourished.