Co-ingesting whey protein with dual source carbohydrate enhances amino acid availability without compromising post-exercise liver glycogen resynthesis

We examined the effects of ingesting maltodextrin and/or fructose with protein co-ingestion on post-exercise liver and muscle glycogen resynthesis. Following glycogen-depleting exercise, ten well-trained male cyclists ingested 60 g.h-1 CHO from either maltodextrin (MAL), fructose (FRU), 1:1 ratio of maltodextrin + fructose (MF) or 1:1 ratio of maltodextrin + fructose plus 30 g whey protein at 0 and 180 min (PRO) during a 5-h recovery period. 13C magnetic resonance spectroscopy and imaging were performed at 0, 120 and 300 min post-exercise to determine liver and muscle glycogen concentrations and liver volume. Protein co-ingestion resulted in elevated serum insulin and plasma glucagon compared with FRU and MF (P < 0.001 for all). Similarly, serum insulin and plasma glucagon concentrations were markedly higher with MAL when compared with both FRU and MF (P < 0.05 for all), although plasma glucagon was also higher when compared with PRO (P < 0.001). Liver glycogen concentrations were significantly higher with FRU (275 ± 49 mmol·L-1), MF (255 ± 50 mmol·L-1) and PRO (283 ± 50 mmol·L-1) compared with MAL (204 ± 51 mmol·L-1) (P < 0.05 for all) following 5 hours of recovery. However, muscle glycogen concentrations (MAL, 168 ± 33; FRU, 145 ± 32; MF, 151 ± 33; PRO 153 ± 33, mmol·L-1) were not different between trials (P > 0.05). We conclude that, despite enhancing glucagonemia, co-ingestion of whey protein (to a 1:1 combination of maltodextrin and fructose) does not compromise post-exercise liver glycogen resynthesis, allowing for increased aminoacidemia alongside rapid glycogen resynthesis.