Exercise-Induced Dehydration Limits the Effectiveness of Post-Exercise Whey Protein Supplementation in Healthy Young...

Post-exercise protein ingestion is widely used to promote recovery from exercise, but whether exercise-induced dehydration limits the subsequent protein supplementation response remains unclear. This study examined the effects of different hydration strategies during exercise on post-exercise whey protein supplementation.

Thirteen healthy young men completed three partially crossover trials designed to produce approximately 2% (DEH: a dehydration trial without fluid replacement), 1% (EUH_50%: a 50% fluid-replacement trial), and 0% (EUH: a euhydration trial with 100% fluid replacement) body mass loss. Within 5 min after each exercise, participants ingested 45 g of whey protein dissolved in 450 mL of water. Serum amino acid concentrations were measured before exercise, immediately after exercise, and at 60 and 120 min after ingestion.

The protocol produced distinct exercise hydration status, with body mass loss of 2.20 ± 0.19% (DEH), 1.18 ± 0.30% (EUH_50%), and 0.27 ± 0.35% (EUH), respectively. Post-exercise whey protein ingestion increased serum amino acid concentrations in all trials. However, at 60 min after ingestion, the DEH trial showed lower total amino acid, branched-chain amino acid, leucine, isoleucine, and glutamine concentrations than both EUH_50% and EUH (all p < 0.05). The 0-120 min percentage incremental area under the curve for total amino acids, branched-chain amino acids, isoleucine, and glutamine was also lower in DEH. Gastrointestinal symptoms remained low across all conditions, with only 1.0% of individual item scores exceeding 4.

These findings indicate that exercise-induced hypohydration of approximately 2.2% body mass attenuates the early circulating amino acid response to post-exercise whey protein ingestion, suggesting that inadequate fluid intake during exercise may compromise the efficacy of whey protein supplementation for post-exercise recovery.