Effects of two glucose ingestion rates on substrate utilization during moderate-intensity shivering

Although the importance of food consumption to survive in the cold is well established, most shivering studies have focused on fuel selection in fasting subjects. Therefore, the aim of the present study was to provide the first estimates of exogenous glucose as well as liver and muscle glycogen oxidation rates of non-cold acclimatized men (n = 6) ingesting glucose in trace amounts (Control; C), and at rates of 400 mg min(-1) (Low Glucose; LG), and 800 mg min(-1) (High Glucose; HG) during moderate-intensity shivering (similar to 3 times resting metabolic rate or similar to 20% VO2max) using indirect calorimetry and stable isotope methodologies. Exogenous glucose oxidation peaked at similar to 200 mg min(-1) at the lowest glucose ingestion rate (similar to 400 mg min(-1)). In addition, glucose ingestion increased the contribution of plasma glucose to total heat production by similar to 50% but did not change the role played by muscle glycogen (similar to 27% of heat production for control condition and similar to 23-28% for LG and HG). Instead, the contribution of liver-derived glucose to total heat production was reduced by 40-60% in LG and HG, respectively. In conclusion, glucose ingestion even at low rates contributes a significant proportion of total heat production during moderate intensity shivering and reduces the utilization of liver-derived glucose but not muscle glycogen.