Metabolic flexibility is unimpaired during exercise in the cold following acute glucose ingestion in young healthy adults

• Published in: Journal of thermal biology Vol. 98; p. 102912
• Main Authors: McCue, Alexus, Munten, Stephanie, Herzig, Karl-Heinz, Gagnon, Dominique D.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.05.2021; Elsevier BV
• Subjects: Calorimetry; Cold; Exercise; Fatigue; Flexibility; Glucose; Health; High fat diet; Indirect calorimetry; Lactic acid; Lipid peroxidation; Lipids; Metabolic disorders; Metabolism; Mitochondria; Oxidation; Thermal stress; Thermal stress; Exercise; Metabolism; Indirect calorimetry; Health
• ISSN: 0306-4565; 1879-0992
• DOI: 10.1016/j.jtherbio.2021.102912

Metabolic flexibility is compromised in individuals suffering from metabolic diseases, lipo- and glucotoxicity, and mitochondrial dysfunctions. Exercise studies performed in cold environments have demonstrated an increase in lipid utilization, which could lead to a compromised substrate competition, glycotoxic-lipotoxic state, or metabolic inflexibility. Whether metabolic flexibility is altered during incremental maximal exercise to volitional fatigue in a cold environment remains unclear. Ten young healthy participants performed four maximal incremental treadmill tests to volitional fatigue, in a fasted state, in a cold (0 °C) or a thermoneutral (22.0 °C) environment, with and without a pre-exercise ingestion of a 75-g glucose solution. Metabolic flexibility was assessed via indirect calorimetry using the change in respiratory exchange ratio (ΔRER), maximal fat oxidation (ΔMFO), and where MFO occurred along the exercise intensity spectrum (ΔFatmax), while circulating lactate and glucose levels were measured pre and post exercise. Multiple linear mixed-effects regressions revealed an increase in glucose oxidation from glucose ingestion and an increase in lipid oxidation from the cold during exercise (p < 0.001). No differences were observed in metabolic flexibility as assessed via ΔRER (0.05 ± 0.03 vs. 0.05 ± 0.03; p = 0.734), ΔMFO (0.21 ± 0.18 vs. 0.16 ± 0.13 g min−1; p = 0.133) and ΔFatmax (13.3 ± 19.0 vs. 0.6 ± 21.3 %V̇O2peak; p = 0.266) in cold and thermoneutral, respectively. Following glucose loading, metabolic flexibility was unaffected during exercise to volitional fatigue in a cold environment, inducing an increase in lipid oxidation. These results suggest that competing pathways responsible for the regulation of fuel selection during exercise and cold exposure may potentially be mechanistically independent. Whether long-term metabolic influences of high-fat diets and acute lipid overload in cold and warm environments would impact metabolic flexibility remain unclear. [Display omitted] •Metabolic flexibility allows shifting between carbohydrates and fat as energy sources.•Exercising in a cold environment increases fat oxidation and could regulate metabolic flexibility.•Metabolic flexibility from an acute glucose ingestion was unaffected during exercise to volitional fatigue in the cold.•Competing pathways regulating fuel selection during exercise and cold exposure may be mechanistically independent.