Fructose Coingestion Does Not Accelerate Postexercise Muscle Glycogen Repletion

BACKGROUND: Post-exercise muscle glycogen repletion is largely determined by the systemic availability of exogenous carbohydrate provided. PURPOSE: This study aimed to assess the effect of the combined ingestion of fructose and glucose on post-exercise muscle glycogen repletion when optimal amounts of carbohydrate are ingested. METHODS: Fourteen male cyclists (age: 28+/-6 y; Wmax: 4.8+/-0.4 W.kg) were studied on 3 different occasions. Each test day started with a glycogen-depleting exercise session. This was followed by a 5 h recovery period, during which subjects ingested 1.5 g.kg.h glucose (GLU), 1.2 g.kg.h glucose + 0.3 g.kg.h fructose (GLU+FRU), or 0.9 g.kg.h glucose + 0.6 g.kg.h sucrose (GLU+SUC). Blood samples and gastrointestinal distress questionnaires were collected frequently and muscle biopsies were obtained at 0, 120, and 300 min after cessation of exercise to measure muscle glycogen content. RESULTS: Plasma glucose responses did not differ between treatments (ANOVA, P=0.096), but plasma insulin and lactate concentrations were elevated during GLU+FRU and GLU+SUC when compared to GLU (P<0.01). Muscle glycogen content immediately following exercise averaged 207+/-112, 219+/-107 and 236+/-118 mmol.kg dry weight in the GLU, GLU+FRU and GLU+SUC treatment, respectively (P=0.362). Carbohydrate ingestion increased muscle glycogen concentrations during 5 h of post-exercise recovery to 261+/-98, 289+/-130 and 315+/-103 mmol.kg dry weight in the GLU, GLU+FRU and GLU+SUC treatment, respectively (P<0.001), with no differences between treatments (time x treatment, P=0.757). CONCLUSION: Combined ingestion of glucose plus fructose does not further accelerate post-exercise muscle glycogen repletion in trained cyclists when ample carbohydrate is ingested. Combined ingestion of glucose (polymers) plus fructose or sucrose reduces gastrointestinal complaints when ingesting large amounts of carbohydrate