Tim Podlogar, Brandon J Shad, Alex P Seabright, Oliver J Odell, Samuel O Lord, Rita Civil, Rafael B Salgueiro, Emma L Shepherd, Patricia F Lalor, Yasir S Elhassan, Yu-Chiang Lai, David S Rowlands, Gareth A Wallis
Journal: American journal of physiology. Endocrinology and metabolism 2023;325(6):E672-E681
PMID: 37850935
Exhaustive endurance exercise results in substantial reductions in skeletal-muscle glycogen content. Following exhaustive endurance exercise, at least 24 h of high dietary-carbohydrate ingestion is required to attain complete repletion of skeletal-muscle glycogen content. Accordingly, nutritional strategy is particularly important when the time between successive exercise bouts is limited. This study aimed to compare the effectiveness of glucose, galactose, and a combination of galactose and glucose in promoting muscle glycogen synthesis during the recovery period after exhaustive exercise. This study was a double-blind, randomised study involving 9 participants (7 men and 2 women). Each participant completed three trials of exhaustive cycling exercise followed by a 4-hour recovery period. During recovery, they ingested carbohydrates at a rate of 1.2 g/kg/h in the form of glucose (GLU), galactose (GAL), or a combination of galactose and glucose (GAL + GLU) in a 1:2 ratio. Results showed that: - ingestion of GAL + GLU resulted in lower muscle glycogen synthesis compared to the ingestion of an isocaloric amount of GLU. - exclusive ingestion of GAL resulted in lower muscle glycogen synthesis compared to GLU. - GAL-only ingestion resulted in muscle glycogen synthesis comparable to that of combined GAL + GLU ingestion. Authors concluded that postexercise galactose-glucose coingestion results in a lower rate of skeletal-muscle glycogen replenishment compared with exclusive glucose-only ingestion. Thus, these findings suggest that glucose should be the preferred carbohydrate source for rapid muscle glycogen replenishment during recovery.
Ingested galactose can enhance postexercise liver glycogen repletion when combined with glucose but effects on muscle glycogen synthesis are unknown. In this double-blind randomized study participants [7 men and 2 women; V̇o: 51.1 (8.7) mL·kg·min] completed three trials of exhaustive cycling exercise followed by a 4-h recovery period, during which carbohydrates were ingested at the rate of 1.2 g·kg·h comprising glucose (GLU), galactose (GAL) or galactose + glucose (GAL + GLU; 1:2 ratio). The increase in vastus lateralis skeletal-muscle glycogen concentration during recovery was higher with GLU relative to GAL + GLU [contrast: +50 mmol·(kg DM); 95%CL 10, 89; = 0.021] and GAL [+46 mmol·(kg DM); 95%CL 8, 84; = 0.024] with no difference between GAL + GLU and GAL [-3 mmol·(kg DM); 95%CL -44, 37; = 0.843]. Plasma glucose concentration in GLU was not significantly different vs. GAL + GLU (+ 0.41 mmol·L; 95%CL 0.13, 0.94) but was significantly lower than GAL (-0.75 mmol·L; 95%CL -1.34, -0.17) and also lower in GAL vs. GAL + GLU (-1.16 mmol·; 95%CL -1.80, -0.53). Plasma insulin was higher in GLU + GAL and GLU compared with GAL but not different between GLU + GAL and GLU. Plasma galactose concentration was higher in GAL compared with GLU (3.35 mmol·L; 95%CL 3.07, 3.63) and GAL + GLU (3.22 mmol·L; 95%CL 3.54, 2.90) with no difference between GLU + GAL (0.13 mmol·L; 95%CL -0.11, 0.37) and GLU. Compared with galactose or a galactose + glucose blend, glucose feeding was more effective in postexercise muscle glycogen synthesis. Comparable muscle glycogen synthesis was observed with galactose-glucose coingestion and exclusive galactose-only ingestion. Postexercise galactose-glucose coingestion or exclusive galactose-only ingestion resulted in a lower rate of skeletal-muscle glycogen replenishment compared with exclusive glucose-only ingestion. Comparable muscle glycogen synthesis was observed with galactose-glucose coingestion and exclusive galactose-only ingestion.
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