Purpose: Current understanding of exogenous CHO metabolism during cold exposure is limited but suggests that exogenous glucose oxidation reaches a maximum of ~200 mg · min(-1) at a glucose ingestion rate of 400 mg · min(-1). The aim of the present study was to determine whether ingesting glucose in combination with fructose (GLU + FRU) after 60 min of cold exposure could increase the rate of exogenous CHO oxidation and reduce the reliance on endogenous CHO reserves compared with ingesting a glucose drink (GLU).
Methods: Six healthy non-cold-acclimatized men were exposed to low-intensity shivering (~2.5 times resting metabolic rate) for a duration of 150 min on two occasions. Subjects consumed a (13)C-enriched CHO drink ((13)C-enriched glucose and fructose) providing 400 mg · min(-1) of glucose + 400 mg · min(-1) of fructose (GLU + FRU) or 800 mg · min(-1) of glucose alone (GLU) after 60 min of cold exposure.
Results: The peak exogenous CHO oxidation rate was 30% greater in GLU + FRU compared with GLU (209 ± 62 vs 159 ± 42 mg · min(-1), respectively, P < 0.05). This contributed to a 16% increase in total CHO oxidation (406 ± 100 vs 351 ± 80 mg · min(-1), respectively, P < 0.05). The utilization of endogenous CHO sources was the same between experimental conditions but was nearly 2.5 times lower than values previously reported by our laboratory when only water was ingested (192-197 vs 456 mg · min(-1), respectively).
Conclusions: This study demonstrates that the greater exogenous and total CHO oxidation rate observed in the GLU + FRU condition was a result of increased systemic appearance of CHO from consuming multiple transportable CHO and/or the supplementary substrate provided from fructose conversion to glucose and lactate in the liver.