Fructose and Galactose Enhance Postexercise Human Liver Glycogen Synthesis

Abstract

Both liver and muscle glycogen stores play a fundamental role in exercise and fatigue, but the effect of different CHO sources on liver glycogen synthesis in humans is unclear. The aim was to compare the effect of maltodextrin (MD) drinks containing galactose, fructose, or glucose on postexercise liver glycogen synthesis. In this double-blind, triple crossover, randomized clinical trial, 10 well-trained male cyclists performed three experimental exercise sessions separated by at least 1 wk. After performing a standard exercise protocol to exhaustion, subjects ingested one of three 15% CHO solutions, namely, FRU (MD + fructose, 2:1), GAL (MD + galactose, 2:1), or GLU (MD + glucose, 2:1), each providing 69 g CHO·h(-1) during 6.5 h of recovery. Liver glycogen changes were followed using (13)C magnetic resonance spectroscopy. Liver glycogen concentration increased at faster rates with FRU (24 ± 2 mmol·L(-1)·h(-1), P < 0.001) and with GAL (28 ± 3 mmol·L(-1)·h(-1), P < 0.001) than with GLU (13 ± 2 mmol·L(-1)·h(-1)). Liver volumes increased (P < 0.001) with FRU (9% ± 2%) and with GAL (10% ± 2%) but not with GLU (2% ± 1%, NS). Net glycogen synthesis appeared linear and was faster with FRU (8.1 ± 0.6 g·h(-1), P < 0.001) and with GAL (8.6 ± 0.9 g·h(-1), P < 0.001) than with GLU (3.7 ± 0.5 g·h(-1)). When ingested at a rate designed to saturate intestinal CHO transport systems, MD drinks with added fructose or galactose were twice as effective as MD + glucose in restoring liver glycogen during short-term postexercise recovery.