DIET AND BODY-COMPOSITION AS DETERMINANTS OF BASAL LIPOLYSIS IN HUMANS

Determinants of basal lipolysis were investigated in a group of 23 vol unteers of both sexes. Body composition was measured by underwater wei ghing and resting metabolic rate with indirect calorimetry. Insulin se nsitivity was determined by using the minimal model of Bergman. The ra te of appearance of palmitic acid in the blood was measured with C-14- 1-palmitate as the tracer administered as a nonprimed constant infusio n. Simple and stepwise-regression analyses were performed to determine correlations and to generate a multivariate model to examine the dete rminants of basal lipolysis. Fat intake (as a percent of total energy intake) was correlated with basal lipolysis (r = 0.57, P < 0.005) as w ell as protein intake (as a percent of energy intake) (r = -0.46, P = 0.03) in univariate analysis. Body weight (r = 0.56, P = 0.005) explai ned a greater portion of the variance in lipolysis than fat-free mass (r = 0.44, P < 0.05) or fat mass (NS). Independent predictors of basal lipolysis were determined by stepwise regression. The best model gene rated included fat intake, fat-free mass, carbohydrate intake, and dai ly energy intake as significant determinants of lipolysis (r = 0.89, P < 0.001). The insulin sensitivity index and sex were not independent predictors of basal lipolysis. Thus, our data support either body weig ht or fat-free mass as more appropriate indexes than fat mass to norma lize basal rates of lipolysis in humans. Furthermore, the macronutrien t composition of the diet is an important determinant of lipolysis and thus should be considered in future experimental designs.