Is energy substrate mobilization a limiting factor for cold thermogenesis?
Energy substrate mobilization has been suggested as being a limiting factor for the rate of cold-induced thermogenesis (M), and consequently in delaying hypothermia. The evidence supporting this hypothesis in humans, however, is not convincing and the hypothesis has yet to be tested in a rigorous manner using a full heat balance analysis (partitional calorimetry). The goal of this study was therefore to re-investigate whether enhancing energy substrate mobilization by feeding cold-exposed subjects would improve M and affect heat debt (S; the minute-by-minute balance of M and heat losses) as well as rectal (Tre) and mean skin temperatures (Tsk). Nine healthy semi-nude fasted subjects were exposed to 5 degrees C (3 h at rest, 1 m.s-1 wind) on three occasions following the ingestion at min 0 and 90 of either: (1) a placebo, (2) 710 kJ of pure carbohydrates (100%-CHO), or (3) 710 kJ of a high-carbohydrate bar (High-CHO). As expected in the cold, Tre and Tsk decreased whereas M, S and heat losses increased (P < 0.01). However, there were no differences between treatments, including the final Tre [mean (SEM); 36.4 (0.2); 36.5 (0.3) and 36.5 (0.2) degrees C for the placebo, 100%-CHO and High-CHO tests, respectively]. During the 100%-CHO treatment, rates of carbohydrate oxidation were the highest and fat oxidation the lowest (P < 0.05), whereas the High-CHO treatment caused smaller changes.(ABSTRACT TRUNCATED AT 250 WORDS)
Vallerand
A L
AL
Defence and Civil Institute of Environmental Medicine, Environmental Physiology Section, North York, Ontario, Canada.
Tikuisis
P
P
Ducharme
M B
MB
Jacobs
I
I
D000328:Adult; D000704:Analysis of Variance; D001831:Body Temperature; D001833:Body Temperature Regulation; D050260:Carbohydrate Metabolism; D003080:Cold Temperature; D004734:Energy Metabolism; D006801:Humans; D008297:Male; D010084:Oxidation-Reduction; D012007:Rectum / Q000502:physiology; D012881:Skin Temperature