Glucose ingestion during exercise blunts exercise induced gene expression of skeletal muscle fat oxidative genes

Ingestion of carbohydrate during exercise may blunt the stimulation of fat oxidative pathways by raising plasma insulin and glucose concentrations and lowering plasma free fatty acids (FFA) levels, thereby causing a marked shift in substrate oxidation. We investigated the effects of a single 2 hour bout of moderate-intensity exercise on the expression of key genes involved in fat and carbohydrate metabolism with or without glucose ingestion in seven healthy untrained men [22.7 +/- 0.6 y; BMI: 23.8 +/- 1.0 kg/m(2); VO2 max: 3.85 +/- 0.21 l/min]. Plasma FFA concentration increased during exercise (p<0.01) in the fasted state but remained unchanged after glucose ingestion whereas fat oxidation (indirect calorimetry) was higher in the fasted state vs. glucose feeding (p<0.05). Except for a significant decrease in the expression of pyruvate dehydrogenase kinase 4 (PDK4; p<0.05), glucose ingestion during exercise produced minimal effects on the expression of genes involved in carbohydrate utilization. However, glucose ingestion resulted in a decrease in the expression of genes involved in FA transport and oxidation (CD36, CPT-1, UCP3 and AMPK-alpha2; p<0.05). In conclusion, glucose ingestion during exercise decreases the expression of genes involved in lipid metabolism rather than increasing genes involved in carbohydrate metabolism.