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, 10 well-trained male cyclists ingested 60 g h⁻¹ carbohydrate 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 following 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 h of recovery. However, muscle glycogen concentrations (mmol L⁻¹: MAL, 168 ± 33; FRU, 145 ± 32; MF, 151 ± 33; PRO 153 ± 33) were not different between trials (P > 0.05). We conclude that, despite enhancing glucagonaemia, 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 aminoacidaemia alongside rapid glycogen resynthesis. (Figure presented.). Key points: Endurance athletes commonly co-ingest carbohydrate and protein within the post-exercise recovery period to facilitate rapid glycogen repletion and muscle remodelling. Here we report that the ingestion of dual-source carbohydrate (a 1:1 ratio of maltodextrin and fructose) enhances liver glycogen repletion when compared with maltodextrin alone. Co-ingesting whey protein alongside this dual-source carbohydrate enhanced amino acid availability without compromising liver glycogen resynthesis, despite enhanced glucagonaemia. These data demonstrate that the co-ingestion of whey protein with dual-source carbohydrate provides a practical strategy to enhance amino acid availability (which provides an important substrate for post-exercise muscle remodelling) and rapid glycogen resynthesis.