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Is energy substrate mobilization a limiting factor for cold thermogenesis?
A L Vallerand1, P Tikuisis, M B Ducharme
1Defence and Civil Institute of Environmental Medicine, Environmental Physiology Section, North York, Ontario, Canada.
Summary
Feeding cold-exposed individuals did not enhance cold-induced thermogenesis (M) or prevent hypothermia. This study found no significant differences in core body temperature between placebo, pure carbohydrate, and high-carbohydrate bar treatments.
Area of Science:
- Human physiology
- Environmental physiology
- Metabolic studies
Background:
- Cold-induced thermogenesis (M) is vital for maintaining body temperature in cold environments.
- Energy substrate mobilization is hypothesized to limit M and delay hypothermia.
- Previous human studies lack rigorous heat balance analysis.
Purpose of the Study:
- To investigate if enhancing energy substrate mobilization by feeding improves M in cold-exposed humans.
- To determine the effect of feeding on heat debt (S), rectal temperature (Tre), and mean skin temperature (Tsk).
Main Methods:
- Nine healthy, fasted subjects were exposed to 5°C with 1 m.s-1 wind for 3 hours.
- Subjects received either a placebo, pure carbohydrates (100%-CHO), or a high-carbohydrate bar (High-CHO) at 0 and 90 minutes.
- Partitional calorimetry was used to measure heat balance, including M, S, heat losses, Tre, and Tsk.
Main Results:
- Cold exposure decreased Tre and Tsk while increasing M, S, and heat losses, as expected.
- No significant differences in final Tre were observed between the placebo, 100%-CHO, and High-CHO treatments.
- The 100%-CHO treatment maximized carbohydrate oxidation and minimized fat oxidation compared to other treatments.
Conclusions:
- Enhancing energy substrate mobilization through carbohydrate feeding does not improve cold-induced thermogenesis (M) in semi-nude, fasted humans.
- Dietary interventions with carbohydrates do not appear to significantly alter heat debt or core body temperature during acute cold exposure.
- The hypothesis that substrate availability limits M in the cold requires further investigation with different experimental designs or populations.