Glucose-fructose beverages do not alter the effects of training on lactate metabolism

Glucose-fructose beverages do not alter the effects of training on lactate metabolism Rosset R., Egli L., Cros J., Schneiter P. and Tappy L. and Lecoultre V. Department of Physiology, University of Lausanne, Lausanne, Switzerland. Introduction It is generally accepted that lactate is produced by skeletal muscle during exercise, and is either used in adjacent muscle fibers (lactate shuttle) or recycled to glucose in the liver. We have shown that ingestion of fructose-containing drinks stimulates lactate production and release from the liver during exercise, and that fructose-derived lactate is subsequently used as an energy substrate by muscle. The regulation of this liver to muscle fructose-lactate shuttle remains unknown. In this study, we assessed whether consumption of fructose-containing beverages alters the effects of training on fructose and lactate metabolism. Methods Two groups of eight sedentary male subjects were endurance-trained for three weeks while ingesting 489 mL/h of either a 9.8%-glucose 6.2%-fructose beverage (GLUFRU) or water (C) during exercise training sessions. An incremental test to exhaustion and a metabolic test were performed before and after the interventions to assess training adaptations and substrate use during endurance-type exercise. Indirect calorimetry, [1-13C]lactate and [6,6-2H2]glucose were used to calculate plasma lactate appearance, clearance and oxidation and glucose kinetics. Results Anthropometrics and performance parameters were similar in both groups at baseline. Plasma glucose concentrations (+1±3 vs. +3±3 % vs. baseline values), glucose rate of appearance (+3±7 vs. +2±3 %) and metabolic clearance (+6±8 vs. +1±5 %) remained stable after both GLUFRU and C training (all p=n.s.). Overall, lactate concentrations were decreased after intervention in both GLUFRU and C, but not differently between groups (-10±5 vs. -20±4 %; p<0.01 vs. baseline, p=n.s. between GLUFRU and C), as a result of an increased lactate metabolic clearance (+26.5±11.4 vs. +17.5±10.2 mL·min-1; p=0.01 vs. baseline, p=0.56 between GLUFRU and C). Lactate appearance (+10±6 vs. -4±9 %) and oxidation (+9±6 vs. - 6±9 %) remained unchanged across time and conditions (all p=n.s.). Maximal oxygen consumption (+287±53 vs. +249±104 mL·min-1) and power eliciting lactate threshold (+25±5 vs. +25±8 W) were similarly increased in GLUFRU and C (both p<0.01 vs. baseline, p=n.s. between GLUFRU and C). Discussion These data corroborate our earlier observation that fructose is converted into lactate by the liver and subsequently oxidized during exercise. Endurance training did not alter liver lactate release, but increased lactate metabolic clearance. The effects of endurance training were not differently altered by the consumption of fructose during training sessions, however