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Citation

Edinburgh RM, Hengist A, Smith HA, Travers RL, Koumanov F, Betts JA, Thompson D, Walhin J, Wallis GA, Hamilton DL, Stevenson EJ, Tipton KD & Gonzalez JT (2018) Preexercise Breakfast Ingestion versus Extended Overnight Fasting Increases Postprandial Glucose Flux after Exercise in Healthy Men. American Journal of Physiology-Endocrinology and Metabolism, 315 (5), pp. E1062-E1074. https://doi.org/10.1152/ajpendo.00163.2018

Abstract
Aims To characterize postprandial glucose flux after exercise in the fed versus overnight fasted-state and to investigate potential underlying mechanisms. Methods In a randomized order, twelve men underwent breakfast-rest (BR; 3 h semi-recumbent), breakfast-exercise (BE; 2 h semi-recumbent before 60-min of cycling (50% peak power output) and overnight fasted-exercise (FE; as per BE omitting breakfast) trials. An oral glucose tolerance test (OGTT) was completed post-exercise (post-rest on BR). Dual stable isotope tracers ([U-13C] glucose ingestion and [6,6-2H2] glucose infusion) and muscle biopsies were combined to assess postprandial plasma glucose kinetics and intramuscular signaling, respectively. Plasma intestinal fatty acid binding (I-FABP) concentrations were determined as a marker of intestinal damage. Results Breakfast before exercise increased post-exercise plasma glucose disposal rates during the OGTT, from 44 g?120 min-1 in FE [35 to 53 g?120 min-1] (mean [normalized 95% CI]) to 73 g?120 min-1 in BE [55 to 90 g?120 min-1; p = 0.01]. This higher plasma glucose disposal rate was, however, offset by increased plasma glucose appearance rates (principally OGTT-derived), resulting in a glycemic response that did not differ between BE and FE (p = 0.11). Plasma I-FABP concentrations during exercise were 264 pg?mL-1 [196 to 332 pg?mL-1] lower in BE versus FE (p = 0.01). Conclusion Breakfast before exercise increases post-exercise postprandial plasma glucose disposal, which is offset (primarily) by increased appearance rates of orally-ingested glucose. Therefore, metabolic responses to fed-state exercise cannot be readily inferred from studies conducted in a fasted state.

Keywords
Physiology (medical); Physiology; Endocrinology, Diabetes and Metabolism

Journal
American Journal of Physiology-Endocrinology and Metabolism: Volume 315, Issue 5

• Published version