Not Drinking Water During Workouts May Affect the Body's Response to Whey Protein: Study - Video

Exercise-induced dehydration may weaken the body's early amino acid response to whey protein supplementation, potentially affecting post-workout recovery, according to a study published in Nutrients.

Whey protein is widely used after exercise because it is rapidly digested and provides amino acids needed for muscle recovery. However, researchers investigated whether inadequate fluid replacement during exercise could influence circulating amino acid levels following protein intake.

The study included 13 healthy young men with an average age of 22.7 years. Participants completed three treadmill exercise trials under different hydration conditions: dehydration without fluid replacement, replacement of 50% of fluid losses, and complete fluid replacement.

After exercise, participants consumed 45 grams of whey protein isolate mixed with 450 millilitres of water. Researchers collected blood samples before and after exercise and at 60 and 120 minutes following supplementation to measure circulating amino acid concentrations.

Body mass loss reached 2.2% during the dehydration trial, compared with 1.2% with partial fluid replacement and 0.3% with complete replacement.

Results showed that dehydration significantly reduced concentrations of total amino acids, branched-chain amino acids (BCAAs), leucine, isoleucine and glutamine 60 minutes after protein ingestion compared with both fluid-replacement conditions.

Overall amino acid responses during the two-hour recovery period were also lower under dehydration for several measures. However, replacing 50% of fluid losses produced amino acid responses comparable to complete fluid replacement.

Researchers suggested that dehydration could influence gastric emptying, intestinal blood flow or amino acid processing. However, these mechanisms were not directly investigated.

The study also found increased thirst and perceived exertion during dehydration, while gastrointestinal symptoms remained generally low across all conditions.

The findings suggest that hydration status may influence the early circulating amino acid response to post-exercise protein supplementation.

Further studies are needed to establish whether adequate hydration improves muscle recovery and long-term training outcomes.

REFERENCE: Xin, Z., Gao, M., Wu, X., et al. (2026). Exercise-Induced Dehydration Limits the Effectiveness of Post-Exercise Whey Protein Supplementation in Healthy Young Men. Nutrients 18(19). DOI: 10.3390/nu18193267