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Modeling of lipid and protein depletion during total starvation

Centre d'Ecologie et Physiologie Energétiques, Centre National de la Recherche Scientifique/Unité Propre de Recherche 9010, 67087 Strasbourg, France

Submitted 11 September 2003 ; accepted in final form 21 May 2004

This study presents a model describing lipid and protein depletion of an individual facing total starvation. The model distinguishes two compartments of body mass: a metabolic compartment and a structural compartment. It is considered that the lipids and the proteins of the metabolic compartment ensure the totality of physiological functions. The main assumptions of the model lie in the definitions of lipid mass and protein mass of the metabolic compartment, which are related to total lipid mass and total body mass, respectively. Under these assumptions, for a given individual, the ratio of lipid and protein utilization rates is proportional to the adiposity. The model accounts for the protein sparing observed at high adiposity levels and enables us to discuss the individual's survival in relation to the levels of lipid and protein depletion. The time course of changes in lipid and protein depletion rates can be calculated by introducing the energy expenditure of the individual. In simulations, it was assumed that specific energy expenditure was constant during starvation and that mortality occurred at a critical level of protein depletion. The most characteristic results derived from these simulations concern the kinetics of protein depletion, which depend markedly on initial adiposity. Accordingly, in obese subjects, the rate of protein losses remains fairly constant during fasting, whereas it increases from the onset of the fast in lean subjects, in agreement with experimental observations. In the model, protein and lipid depletion rates are both proportional to energy expenditure, which needs to be confirmed from complementary data.

body composition; protein sparing; energy expenditure

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