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We have summarized relevant
information on the effects of dietary protein and energy on
hormonal and growth factor regulation of normal and catch-up
growth. We have examined new knowledge on protein-energy
interactions during rapid growth of premature infants and
malnourished children. Finally, we have called attention to the
problem of children with secondary malnutrition who may have a
further compromise of their linear growth because of low-protein
diets given as part of treatment for their primary condition.
Based on present knowledge we suggest the following approach to optimize catch-up growth of children: provide the necessary energy and protein to permit rapid growth for the malnourished; this implies providing that required for normal children of equivalent age, in practice 180-220 kcal/kg with a P/E ratio of 10-12%. In the case of premature infants, the evidence suggests that 120-150 kcal/kg/d and 34 g/kg of protein are sufficient for catch-up growth; the higher range of these intakes is recommended for periods where rates of growth of > 20 g/kg/d are sought. Environmental stimulation, physical activity, and tender loving care are an integral part of this growth-promoting regimen (VIAL, ALVEAR and ARTAZA, 1991).
Based on the newer understanding of protein-energy and growth interactions we speculate that optimization of catch-up growth for the future may additionally include:
1. Use of different P/E ratios depending on stage of nutritional recovery, desirable weight gain, and target body composition. These regimens might need to be individually adjusted using growth rate, urinary N. and serum urea as simple markers of N metabolism. These laboratory measures are available in most settings.
2. The use of high-carbohydrate, high-protein, low-fat regimens during periods of rapid growth to induce higher insulin levels that may serve to enhance N utilization and lean mass accretion.
3. The use of essential and non-essential N compounds such as glutamine, arginine, branched-chain amino acids, or nucleotides as potential growth modulators for specific organs. These compounds may serve to induce hormonal or growth factor responses (i.e., arginine and GH), provide fuels that favor growth of some organs (i.e., glutamine for the gut), spare amino acid oxidation (i.e., branched-chain amino acids sparing muscle protein breakdown), or serve as preformed precursors for tissue synthesis (i.e., nucleotide salvage for nucleic acid synthesis required by rapidly dividing cells).
4. The administration of growth hormone or insulin during periods of rapid growth, or after lean tissue recovery has slowed, to permit better recovery of length and of other tissues where hyperplastic growth is crucial. The potential use of these agents requires that safety considerations be dealt with and that appropriate substrate provision be given to optimize their action.
5. Finally, the use in specific situations of organ-specific growth factors, e.g., IGF-I to promote muscle mass growth and recovery, or EGF to optimize recovery of skin growth after burn injury. The possibility of utilizing other organ-specific growth factors may come when more is learned about them (i.e., nerve growth factor, platelet growth factor, colony-stimulating factor, osteogenic factor). This is by no means a complete list of possibilities.
The authors gratefully
acknowledge the editorial review and helpful suggestions of
Charles Mize, M.D. Ph.D.