Diet and body composition as determinants of basal lipolysis in humans

Determinants of basal lipolysis were investigated in a group of 23 volunteers of both sexes. Body composition was measured by underwater weighing and resting metabolic rate with indirect calorimetry. Insulin sensitivity was determined by using the minimal model of Bergman. The rate of appearance of palmitic acid in the blood was measured with 14C-1-palmitate as the tracer administered as a nonprimed constant infusion. Simple and stepwise-regression analyses were performed to determine correlations and to generate a multivariate model to examine the determinants of basal lipolysis. Fat intake (as a percent of total energy intake) was correlated with basal lipolysis (r = 0.57, P < 0.005) as well 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) explained 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 generated included fat intake, fat-free mass, carbohydrate intake, and daily 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 weight or fat-free mass as more appropriate indexes than fat mass to normalize basal rates of lipolysis in humans. Furthermore, the macronutrient composition of the diet is an important determinant of lipolysis and thus should be considered in future experimental designs.