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/m²; VO_{2 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-2; 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.