Effect of carbohydrate ingestion on glycogen resynthesis in human liver and skeletal muscle, measured by ¹³C MRS

Abstract

This study investigated the effect of carbohydrate (CHO) ingestion on postexercise glycogen resynthesis, measured simultaneously in liver and muscle (n = 6) by (13)C magnetic resonance spectroscopy, and subsequent exercise capacity (n = 10). Subjects cycled at 70% maximal oxygen uptake for 83 +/- 8 min on six separate occasions. At the end of exercise, subjects ingested 1 g/kg body mass (BM) glucose, sucrose, or placebo (control). Resynthesis of glycogen over a 4-h period after treatment ingestion was measured on the first three occasions, and subsequent exercise capacity was measured on occasions four through six. No glycogen was resynthesized during the control trial. Liver glycogen resynthesis was evident after glucose (13 +/- 8 g) and sucrose (25 +/- 5 g) ingestion, both of which were different from control (P < 0.01). No significant differences in muscle glycogen resynthesis were found among trials. A relationship between the CHO load (g) and change in liver glycogen content (g) was evident after 30, 90, 150, and 210 min of recovery (r = 0.59-0. 79, P < 0.05). Furthermore, a modest relationship existed between change in liver glycogen content (g) and subsequent exercise capacity (r = 0.53, P < 0.05). However, no significant difference in mean exercise time was found (control: 35 +/- 5, glucose: 40 +/- 5, and sucrose: 46 +/- 6 min). Therefore, 1 g/kg BM glucose or sucrose is sufficient to initiate postexercise liver glycogen resynthesis, which contributes to subsequent exercise capacity, but not muscle glycogen resynthesis.

Energy replacement attenuates the effects of prior moderate exercise on postprandial metabolism in overweight/obese men

“…This reasoning can also explain why replacement of the exerciseinduced energy deficit substantially attenuated the TGlowering effect. Increased carbohydrate ingestion following exercise markedly increases the rate of both hepatic and muscle glycogen re-synthesis 29 and thus muscle and hepatic substrate deficits would have been substantially smaller following energy replacement than exercise with energy deficit. In addition, increased carbohydrate ingestion per se has been shown to increase fasting and postprandial TG concentrations, probably by increasing hepatic VLDL production, 33 so the increased carbohydrate intake in the exercise with energy replacement trial would have acted to oppose an exercise-induced lowering in TG.…”

Physiological aspects of energy metabolism and gastrointestinal effects of carbohydrates

“…The energy balance can be calculated from changes in body composition (Fuller et al, 1992;Heymsfield et al, 2005), which can provide estimates of fat and protein mass, and in some cases carbohydrate (glycogen stores are small, but can be measured accurately and precisely using nuclear magnetic resonance; Taylor et al, 1992;Casey et al, 2000). Energy balance can also be calculated from classic balance studies, which involve measurement of energy intake and energy expenditure.…”

The Effect of Pre-Exercise Galactose and Glucose Ingestion on High-Intensity Endurance Cycling

“…Pre-exercise muscle and liver glycogen concentrations are essential substrate sources during prolonged moderate to high-intensity exercise, as they are both directly associated with performance (1,2). Athletes typically consume carbohydrates (CHO) prior to and/or during exercise as a means of improving performance and endurance capacity.…”

“…Further, the consumption of galactose within the hour before exercise may have the potential to pre-load the liver with newly synthesised glycogen, for subsequent release, as galactose has to be converted by the liver through the Leloir pathway. This is of particular importance as the liver is as important in sustaining high-intensity exercise as muscle glycogen (2).…”