Abstract
ContextPre-exercise nutrient availability alters acute metabolic responses to exercise, which could modulate training responsiveness.ObjectiveTo 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).SettingGeneral community.ParticipantsMen 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).InterventionsModerate-intensity cycling performed before versus after mixed-macronutrient breakfast (Acute Study) or carbohydrate (Training Study) ingestion.ResultsAcute 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).ConclusionsExperiments 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.
Highlights
Obesity and a sedentary lifestyle are independently associated with changes in skeletal muscle that can reduce insulin sensitivity [4, 5] and increase hyperinsulinemia, contributing to elevated cardiovascular disease risk [2]
Increasing insulin sensitivity and reducing postprandial insulinemia are important targets for interventions to reduce the risk of metabolic disease
The beneficial effects of exercise on oral glucose tolerance and insulin sensitivity can be attributed to both an acute phase and the more enduring molecular adaptations that accrue in response to regular exercise [7]
Summary
Ethical approval This project comprised 2 experiments. We first assessed the acute metabolic and mRNA responses to manipulating nutrient-exercise timing (Acute Study), followed by a 6-week randomized, controlled trial to assess the longer-term adaptations in response to carbohydrate-exercise timing (Training Study). All participants provided informed written consent prior to participation. Potential participants were excluded if they had any condition or were taking any medication known to alter any of the outcome measures. The studies were registered at https://clinicaltrials.gov (NCT02397304 and NCT02744183, respectively). Protocols were approved by the National Health Service Research Ethics Committee (15/WM/0128 and 16/SW/0260, respectively), and experiments were conducted in accordance with the Declaration of Helsinki
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