Lipid metabolism links nutrient-exercise timing to insulin sensitivity in men classified as overweight or obese. Breakfast, exercise and metabolic health

Context: Pre-exercise nutrient availability alters acute metabolic responses to exercise, which could modulate training responsiveness. Objective: To assess acute and chronic effects of exercise performed before versus after nutrient ingestion on whole-body and intramuscular lipid utilization and postprandial glucose metabolism. Design: (1) Acute, randomized, crossover design (Acute Study); (2) 6-week, randomized, controlled design (Training Study). Setting: General community. Participants: Men with overweight/obesity (mean ± standard deviation, body mass index: 30.2 ± 3.5 kg·m ^-2 for Acute Study, 30.9 ± 4.5 kg·m ^-2 for Training Study). Interventions: Moderate-intensity cycling performed before versus after mixed-macronutrient breakfast (Acute Study) or carbohydrate (Training Study) ingestion. Results: Acute Study -exercise before versus after breakfast consumption increased net intramuscular lipid utilization in type I (net change: -3.44 ± 2.63% versus 1.44 ± 4.18% area lipid staining, P < 0.01) and type II fibers (-1.89 ± 2.48% versus 1.83 ± 1.92% area lipid staining, P < 0.05). Training Study -postprandial glycemia was not differentially affected by 6 weeks of exercise training performed before versus after carbohydrate intake (P > 0.05). However, postprandial insulinemia was reduced with exercise training performed before but not after carbohydrate ingestion (P = 0.03). This resulted in increased oral glucose insulin sensitivity (25 ± 38 vs -21 ± 32 mL·min ^-1·m ^-2; P = 0.01), associated with increased lipid utilization during exercise (r = 0.50, P = 0.02). Regular exercise before nutrient provision also augmented remodeling of skeletal muscle phospholipids and protein content of the glucose transport protein GLUT4 (P < 0.05). Conclusions: Experiments investigating exercise training and metabolic health should consider nutrient-exercise timing, and exercise performed before versus after nutrient intake (ie, in the fasted state) may exert beneficial effects on lipid utilization and reduce postprandial insulinemia.