ENERGY-EXPENDITURE AND SUBSTRATES OXIDATIVE PATTERNS, AFTER GLUCOSE, FAT OR MIXED LOAD IN NORMAL-WEIGHT SUBJECTS

Objectives: To evaluate energy balance after three isocaloric oral loa ds of different composition and to establish possible relationships be tween the substrates oxidative patterns and the modifications of insul in and free fatty acids (FFA) plasma profiles. Design: Each subject re ceived, in a randomized order, three oral loads of 2658 +/- 45 kJ (636 +/- 11 Kcal) either as glucose, lipids (cream) or a mixture (glucose + cream). Setting: The experiments were performed at the University Ho spital of Geneva. Subjects: Ten normal body-weight volunteers. Methods : Energy expenditure GEE) and substrates oxidation were measured by in direct calorimetry during 8 h following each load. Plasma glucose, ins ulin and FFA were also measured. Results: EE was 1776 +/- 107, 1818 +/ - 125 and 1785 +/- 117 KJ over 8 h after glucose, mixed and lipids loa d, respectively. Glucose oxidation was the highest after oral glucose as compared to mixed and lipids load, while the highest value of lipid s oxidation was measured after fat load. A significant relationship Li nked fat oxidation to plasma FFA (r= 0.54, P < 0.002) as well as to in sulin (r = - 0.40, P < 0.002). Conclusions: (a) The energetic cost of glucose and fat intake is the same; (2) after each load, the main sour ce of energy corresponds to the substrate administered; (3) both plasm a insulin and FFA influence the substrate oxidative patterns observed after each load; (4) alimentary fat may contribute to fat oxidation by maintaining elevated plasma FFA levels.