Protein and Exercise-Induced Gastrointestinal Symptoms

Context: Proper nutrition is crucial for peak sport performance. Recommendations for carbohydrate intakes in the pre-exercise meal for endurance athletes are available; however, are lacking for protein. Furthermore, a recent position statement regarding nutrient timing for exercise also lacks protein recommendations. The only advice provided is to avoid "too much" as it may cause gastrointestinal (GI) discomfort. The aforementioned recommendation provides no guidance as to how much is "too much" nor, to our knowledge, is there any clinical trial data to support the position. Exercise-associated gastrointestinal symptoms are a common cause of withdrawal from competition; thus, athletes need to consider the impact of dietary choices on gastrointestinal (GI) symptoms, as well as performance. Exercise induced GI symptoms can plague all athletes; but the effects seem to be most pronounced in endurance running. The reported prevalence of exercise-induced GI disturbances varies depending on methodology; however a questionnaire administered by the investigator's lab to 440 runners found 41% experienced stomach pain/cramps, 24% had intestinal issues, and over 20% reported bloating, diarrhea and/or gas. Exercise related GI complaints have been broadly related to diet. Research from the investigator's lab has found that many of the top foods that are avoided pre-running, to reduce GI symptoms, are those classified as high in protein (legumes, meat, poultry, fish, milk). These observations are based on self-reported data from experienced runners, and require testing in a clinical setting.

Objectives: 1) to quantify exercise induced gastrointestinal symptoms and gut fullness occurring in response to a low protein (control) and high protein (intervention) pre-exercise meal. 2) to quantify blood glucose responses to a high protein pre-exercise meal as compared to a low protein control.

Methods: The study is a single blind crossover design. Endurance runners will be ask to standardize their exercise 3-days prior to testing. The participants will be asked to eat a similar meal in the 24-12 hours pre-testing and fast for 12 hours pre-testing. The participants will be assigned to consume a pre-exercise shake with carbohydrate at 0.75g/kg body weight + water at 5ml/kg body weight and either low whey protein control or high whey protein intervention one hour pre-exercise in a randomized fashion. Participants will then complete a 10 km running protocol at 85% of the participant's race pace on a treadmill in an temperature and humidity controlled room. Gastrointestinal symptoms via self-report questionnaire and blood glucose will be measured at fasting, during the one hour digestive period and post-exercise.