Fructose and glucose co-ingestion during prolonged exercise increases lactate and glucose fluxes and oxidation compared with an equimolar intake of glucose

Abstract

Background: When fructose is ingested together with glucose (GLUFRU) during exercise, plasma lactate and exogenous carbohydrate oxidation rates are higher than with glucose alone. Objective: The objective was to investigate to what extent GLUFRU increased lactate kinetics and oxidation rate and gluconeogenesis from lactate (GNGL) and from fructose (GNGF). Design: Seven endurance-trained men performed 120 min of exercise at ≈60% VO 2max (maximal oxygen consumption) while ingesting 1.2 g glucose/min + 0.8 g of either glucose or fructose/min (GLUFRU). In 2 trials, the effects of glucose and GLUFRU on lactate and glucose kinetics were investigated with glucose and lactate tracers. In a third trial, labeled fructose was added to GLUFRU to assess fructose disposal. Results: In GLUFRU, lactate appearance (120 ± 6 μmol·kg-1·min-1), lactate disappearance (121 ± 7 μmol·kg-1·min -1), and oxidation (127 ± 12 μmol·kg -1·min-1) rates increased significantly (P < 0.001) in comparison with glucose alone (94 ± 16, 95 ± 16, and 97 ± 16 μmol·kg-1·min-1, respectively).GNGL was negligible in both conditions. In GLUFRU, GNGF and exogenous fructose oxidation increased with time and leveled off at 18.8 ± 3.7 and 38 ± 4 μmol·kg -1·min-1, respectively, at 100 min. Plasma glucose appearance rate was significantly higher (P < 0.01) in GLUFRU (91 ± 6 μmol·kg-1·min-1) than in glucose alone (82 ± 9 μmol·kg-1·min-1). Carbohydrate oxidation rate was higher (P < 0.05) in GLUFRU. Conclusions: Fructose increased total carbohydrate oxidation, lactate production and oxidation, and GNGF. Fructose oxidation was explained equally by fructose-derived lactate and glucose oxidation, most likely in skeletal and cardiac muscle. This trial was registered at clinicaltrials.gov as NCT01128647. © 2010 American Society for Nutrition.