Control of protein synthesis and its relationship to the bioenergetics of growth

A key goal of nutritional therapies designed to prevent or treat protein energy malnutrition (PEM) is achievement of adequate growth rates and thus positive balances of protein and energy. Positive protein balance is the net result of protein turnover, i.e., of recycling protein through energy-requiring anabolic and catabolic pathways. Thus, protein turnover is inexorably linked to energy metabolism and to energy balance. A long-standing hypothesis is that new tissue synthesis is predominantly a postprandial event. Thus, postprandial rates of protein turnover may regulate the bioenergetics of growth. Traditional methods to evaluate nutritional therapies for diarrhea and PEM, i.e., metabolic balance, 15N-labeled amino acids, fecal output, illness duration, or change in body weight, are not specific to studies of the regulation of acute protein turnover and growth by nutritional intervention. Newer techniques based on 13C-labeled amino acids should be applied to evaluate nutritional interventions such as dietary substrate ratios, protein quality, feeding frequencies, or ratios of dietary protein to energy in terms of their abilities to optimize postprandial protein turnover and thus nutritional management of diarrhea or PEM.