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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.

  • 2026-01-20
  • Journal of the International Society of Sports Nutrition 23(1)
    • Keely Shaw
    • Brynn Lindstrom
    • Amy Moss
    • Jill A Parnell

Study Design

Type
Clinical Trial
Population
13 recreational runners (eight females, five males)
Methods
single-blind crossover study, 10 km treadmill run at 85% of 10 km race pace after consuming a shake with carbohydrate and whey protein at either a low-protein (0.15 g/kg body mass) or moderate-protein (0.4 g/kg body mass) dose 60 minutes prior to exercise
Blinding
Single-blind
Duration
60 minutes prior to exercise plus a 10 km run
Funding
Unclear

Background

Exercise induced gastrointestinal (GI) symptoms affect a significant portion of endurance runners, resulting in discomfort and suboptimal performance. Protein intakes pre-exercise may have benefits; however, research investigating dietary intake prior to exercise suggests that many runners avoid foods high in protein before running to manage their GI symptoms. Unfortunately, clinical trials evaluating the effectiveness of this strategy are lacking. This study aimed to quantify exercise-induced GI symptoms, gut fullness, blood glucose response, and ratings of perceived exertion in response to low-protein (LP) and moderate-protein (MP) pre-exercise shake.

Methods

This single-blind crossover study involved 13 recreational runners (eight females, five males) who completed a 10 km treadmill run at 85% of their 10 km race pace after consuming a shake with carbohydrate and whey protein at either a low-protein (0.15 g/kg body mass) or moderate-protein (0.4 g/kg body mass) dose 60 minutes prior to exercise. Due to increased whey protein and standardized carbohydrate, the shakes had differing energy contents. GI symptoms were assessed pre-shake, 60 minutes post-shake, and post-run using a questionnaire and gut fullness was assessed pre-shake, 15-, 30-, and 60 minutes post-shake, and post-run using a visual analog scale. Blood glucose was measured pre-shake, 30- and 60 minutes post-shake, and post-run using a capillary blood sample and rating of perceived exertion was assessed following the 10 km run.

Results

Total symptoms experienced increased over time (p < 0.01) and were greater during the run than at fasting (p < 0.01) or post-shake (p = 0.01) but were not affected by protein content (p = 0.85). A significant increase in bloating severity was observed following the moderate-protein shake as compared to the low-protein shake during the run (0.54 vs 1.23; p = 0.03), but no other symptoms assessed were significantly impacted by the shake composition. Blood glucose was significantly higher at 30 minutes post-shake than at any other time; however, there was no difference between the shakes (p = 0.20). Gut fullness increased post-shake (p < 0.01) but did not differ significantly between the two conditions at any time point; however, remained above fasting at all time points only in the MP group. Rating of perceived exertion was not significantly different between the two conditions (low-protein = 14.9 ± 1.0; moderate-protein = 14.9 ± 0.7; p = 1.00).

Conclusions

Easily digestible protein sources up to 0.4 g/kg body mass consumed one hour before exercise are advised and generally well tolerated, though 0.4 g/kg body mass of protein was associated with increased bloating. However, protein intakes before exercise should be trialed prior to competition due to variations in individual tolerance.

Research Insights

  • Whey Protein→Increased Bloating

    A significant increase in bloating severity was observed following the moderate-protein shake as compared to the low-protein shake during the run (0.54 vs 1.23; p = 0.03)

    Effect
    Harmful
    Effect size
    Small
    Dose
    0.4 g/kg body mass
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