PROTEIN, FAT, AND CARBOHYDRATE REQUIREMENTS DURING STARVATION - ANAPLEROSIS AND CATAPLEROSIS

The purpose of this work was to clarify the essentiality of glucose pr oduction from amino acids in obese subjects undergoing prolonged starv ation and to provide an explanation for death after the depletion of l ean body mass when some body fat is still available to meet body energ y requirements. Five obese subjects fasted for 21 d. Nitrogen balance studies were combined with measurements of blood metabolite and hormon e concentrations, indirect calorimetry, determination of body-composit ion changes, and catheterization techniques. Phenylacetate was adminis tered from day 19 to day 21 to remove glutamine from the body and to a ssess this perturbation on energy requirements, ammoniagenesis, ureage nesis, gluconeogenesis and ketogenesis. The obese subjects lost body f at and fat-free mass in parallel and resting metabolic energy requirem ents per mass remained constant during starvation. Urinary nitrogen ex cretion reflected continuous demands for amino acid oxidation. Phenyla cetate administration decreased blood glutamine concentrations, increa sed plasma epinephrine concentrations, and increased urinary nitrogen loss through phenylacetylglutamine excretion; urinary excretion rates of urea, ammonium, urate, creatinine, and ketone bodies remained uncha nged. The essentiality of amino acid oxidation was therefore shown. La te in prolonged starvation, aminogenic oxidation amounted to 7% and fa t provided the remaining energy requirements. Hepatic and renal glucon eogenesis were not curtailed. Blood glutamate served as a vehicle for carbon and nitrogen transport; the contribution of glycerol to glucone ogenesis equaled that of all amino acids combined. The minimal quantit ies of amino acid (0.27 plus or minus 0.08 and 0.52 plus or minus 0.10 g) and fat (1.53 plus or minus 0.21 and 2.98 plus or minus 0.15g) oxid ized per kg body wt or fat-free mass/d, respectively, were determined. Included within amino acid and fat oxidation were the minimal amounts of precursors needed for synthesizing the essential quantity of gluco se (0.34 plus or minus 0.14 and 0.66 plus or minus 0.20g) oxidized per kg body wt or fat-free mass, respectively.