Thermogenic effect of slight hyperglycemia during a lipid infusion

Resistance to the glucoregulatory action of insulin is a common finding in obesity and may affect thermogenesis. In 13 healthy subjects, we studied th e influence of acute insulin resistance induced by a lipid infusion on ther mogenesis without any glucose load (n = 4) or during a euglycemic-hyperinsu linemic clamp (n = 5) and an oral glucose tolerance test (OGTT, n = 8). Whe n substrates were not administered at the same time, the energy cost of sto rage was significantly (P < .05) lower for lipids (3.9% +/- 0.9%) than for glucose (11.9% +/- 0.5% during the clamp and 14.9% +/- 4.0% during the OGTT , NS). The lipid infusion decreased glucose storage during the clamp (contr ol, 3.99 +/- 0.40 mg.kg(-1).min(-1); lipid infusion, 0.92 +/- 0.39; P < .05 ) but increased it during the OGTT (control, 1.76 +/- 0.22 mg.kg(-1).min(-1 ); lipid infusion, 2.94 +/- 0.27; P < .05). Infused lipids were stored more (clamp, 3.31 +/- 0.16; OGTT. 2.65 +/- 0.11 mg.kg(-1).min(-1); P < .01) and oxidized less (clamp, 0.64 +/- 0.21; OGTT. 1.02 +/- 0.09 mg.kg(-1).min(-1) ; P<.05) during the clamp than during the OGTT: When lipids were infused, t he energy cost of substrate storage was lower during the clamp versus the O GTT (clamp, 3.2% +/- 0.8%; OGTT, 7.3% +/- 1.0%; P < .05). This effect was a ttributed to a lipid-induced impairment of glucose tolerance, which overcom es the inhibitory effect of lipid infusion on glucose storage observed in e uglycemia. A slight elevation of plasma glucose in response to a lipid infu sion impairs thermogenesis by redirecting the storage of substrates from li pids to glucose, which has a higher energy cost. Copyright (C) 1999 by W.B. Saunders Company.