American Journal of Clinical Nutrition, Vol 27, 175-187, Copyright © 1974 by The American Society for Clinical Nutrition, Inc.

The metabolic fuel regulatory system: implications for protein-sparing therapies during caloric deprivation and disease

¹ From the Unit of Experimental Medicine, Department of Nutrition and Food Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139

A scheme is developed to describe the primary physiological interactions that serve to regulate the supply and the consumption of substrates for energy production. In a highly simplified form, the proposed concept of the metabolic fuel regulatory system shows how carbohydrate, amino acid, and fat metabolism can be integrated.

The scheme is used to analyze the metabolic behavior encountered under conditions of increased protein catabolism. It appears that during periods of caloric deprivation, the anabolic effect of insulin on fat metabolism may enhance protein catabolism by curtailing the mobilization of endogenous fat stores and by preventing starvation ketosis. The implications for nutritional therapies designed with the specific property or aim to preserve the lean body mass during periods of caloric deprivation and disease are discussed.

The close relationship between nitrogen balance and fat mobilization suggests that the favorable or unfavorable effects exerted by various hormones or drugs on protein metabolism may be related largely to their direct or indirect influence on fat mobilization.