Pre-Run Whey Protein Tolerance in Endurance Running: What a New Clinical Trial Found

Gastrointestinal (GI) discomfort can significantly impair performance for runners during races or intense training. Many athletes avoid protein-rich pre-run meals based on conventional advice, yet rigorous evidence investigating how much protein can be tolerated before high-intensity running has been lacking. This question is addressed directly in the clinical trial “Whey protein intakes up to 0.4 g/kg body mass are well tolerated before a 10 km run at 85% of race pace” by Keely Shaw et al, which examined whether consuming moderate amounts of whey protein before a hard run increases gastrointestinal symptoms or alters markers related to exercise tolerance.

Study Design and Participants

Researchers conducted a single-blind crossover clinical trial with 13 recreational runners (8 female, 5 male) who completed a 10 km treadmill run at 85 % of personal race pace after consuming pre-exercise shakes. Each runner participated in two conditions, one week apart:

• Low-protein shake: 0.15 g of whey protein per kg of body mass + carbohydrates
• Moderate-protein shake: 0.40 g of whey protein per kg of body mass + carbohydrates

Shakes were consumed 60 minutes before exercise, with total energy adjusted for the added protein content. GI symptoms, gut fullness, capillary blood glucose, and perceived exertion were measured at multiple time points before and after running.

Key Findings

1. Tolerance of Whey Protein Up to 0.4 g/kg BM

• Both low- and moderate-protein shakes were generally well tolerated, meaning no significant increase in total GI symptoms overall directly attributable to higher protein dose.

2. Bloating Increased With Moderate Protein

• Bloating severity was significantly higher during the run after the moderate-protein (0.4 g/kg) shake compared to the low-protein shake. This was the only GI symptom that differed between conditions.

3. Gut Fullness and Blood Glucose

• Gut fullness increased after both shakes but did not differ significantly between the low- and moderate-protein conditions at any measured time.
• Blood glucose rose after ingestion (as expected with carbohydrate intake), but no difference emerged between protein conditions.

4. Perceived Effort Unchanged

• Ratings of perceived exertion following the run did not differ between the two trials, indicating that added protein neither made the run feel easier nor harder at this pace.

What This Means for Endurance Runners

Practical Takeaways

1. Moderate pre-run protein is generally fine. Easily digestible whey protein up to 0.4 g/kg of body mass consumed about an hour before running does not produce substantially worse GI symptoms compared to a lower protein dose, aside from increased bloating.
2. Bloating is a real individual factor. If you frequently struggle with GI discomfort during races, introducing moderate protein before a key workout or race should be trialed in training first to assess personal tolerance.
3. Performance perception unaffected. Consuming more protein pre-run did not alter how hard runners felt the effort was, suggesting no obvious negative impact on acute performance at this pace.

How This Could Influence Nutrition Planning

• For sessions at race pace or high-intensity efforts, athletes often avoid protein to minimise GI issues. This study suggests that with training, moderate protein intake can be incorporated without substantial detriment—potentially supporting better overall energy and muscle protection strategies.

Limitations and What It Does Not Mean

• The study involved a small sample (n=13) of recreational runners, not elite athletes; responses may differ by fitness level or in competition settings.
• Only whey protein was tested. Other protein sources with different digestion rates might behave differently.
• The study examined only a 10 km run at 85 % race pace; longer durations may amplify GI responses or nutrient effects.

Bottom Line

This clinical trial provides evidence that a moderate amount of whey protein (0.4 g/kg) consumed about an hour before a hard run is generally well tolerated by recreational runners and does not significantly worsen GI symptoms compared to a lower protein dose, aside from some increased bloating. Athletes should still test this strategy in training before racing to ensure individual tolerance.

Disclaimer: The information on this website does not constitute medical advice, nutritional counseling, diagnosis, treatment, or coaching. It is not intended to replace consultation with qualified medical doctors, dietitians, nutritionists, or other licensed professionals.

Any decisions regarding health, nutrition, or training should be made in consultation with appropriately qualified professionals.

Source: Shaw K, Lindstrom B, Moss A, Parnell JA. Whey protein intakes up to 0.4g/kg body mass are well tolerated before a 10km run at 85% of race pace: a clinical trial. J Int Soc Sports Nutr. 2026 Dec 31;23(1):2615270. doi: 10.1080/15502783.2026.2615270. Epub 2026 Jan 20. PMID: 41556283; PMCID: PMC12821340.