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

Abstract 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. image 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.