By Dr Ricardo Costa
Senior Lecturer & Researcher in Exercise Physiology, Metabolism & Dietetics - Monash University
A recent Monash University review of published studies has found that all people who exercise excessively may be prone to acute or chronic gut issues .
The review found that with increasing intensity and duration of exercise, there was a proportional increased risk of gut damage, impaired gut function, and both upper- and lower-gastrointestinal symptoms. Specifically, the cells of the intestine are injured, the gut becomes more “leaky” allowing toxins to pass into the bloodstream resulting in an initial systemic immune response, the gut transit and digestion of food is reduced, and nutrients already in the gut and/or consumed during exercise may be prone to malabsorption. This scenario of 'exercise-induced gastrointestinal syndrome' may lead to acute or chronic health complications, and exacerbate already established conditions including irritable bowel syndrome – IBS.
Strenuous exercise of two hours or more appears to be the threshold whereby significant gut disturbances arise, irrespective of an individual’s fitness status. Running appears to exacerbate the gut disturbances more than other forms of exercise (e.g., cycling), as does exercising in hot ambient temperatures (i.e., ≥30°C).
The study published in Alimentary Pharmacology and Therapeutics did however find that low to moderate activity may be beneficial for symptom management and improving quality of life in IBS patients. Walking programs over 10 -12 weeks and running three times per week did not exacerbate symptoms and were associated with improvements in general well-being. However, for sufferers of IBS, the health and symptoms management implications of more strenuous exercise have not been researched, but likely to be detrimental and a high-risk activity for such patients.
Despite strenuous exercise being confirmed to compromise gut integrity and function, there are several exacerbating factors which can be controlled, and several prevention and management strategies that can attenuate and abolish the damage and compromised function. These include: regulating exercise duration and intensity within individual comfort; ensure optimal hydration before exercise and maintain hydration during exercise; avoid overfeeding and over drinking- identify individual tolerance levels; identify any exercise-associated malabsorption; avoiding non-steroidal anti-inflammatory drugs (e.g., aspirin and ibuprofen) around training and competition schedules; and avoid exercising in hot ambient conditions (e.g., ≥30°C) or if training and/or competing in hot environments ensure heat acclimation/acclimatisation.
Despite further research being warranted to determine the full extent of prolonged strenuous exercise on IBS to establish evidence-based prevention and management guidelines, some practical strategies, aimed at reducing gut symptoms during exercise include :
- Ensure hydration is optimal before starting exercise and maintain hydration during exercise- ad libitum water intake is sufficient to maintain hydration. However, a hydration assessment can identify body water losses (i.e., sweat losses) in response to exercise and how much intake should be on an individual basis (e.g., ml/h).
- Consider lowering the FODMAPs content of the diet prior to periods of heavy training and/or competition. For example, consider reducing the amount of “red rated foods” than normally consumed. There is some evidence to suggest that a 24h low FODMAP diet may reduce both upper- and lower-gastrointestinal symptoms in response to prolonged strenuous exercise.
- Many ‘sport foods’ (e.g., drinks, gels or bars) contain fructose and sorbitol. Known fructose and sorbitol malabsorbers should pay particular attention to avoid these. Use glucose/dextrose/maltodextrin based products and consume small amounts regularly throughout exercise. Note that carbohydrate feeding during exercise is generally only recommended if exercising more than two hours, as the body’s muscle glycogen stores can normally provide sufficient quick fuel for the first two hours.
- Train the gut to tolerate feeding during exercise [2,3]. Practice the proposed race nutrition regime in training on various occasions.
- Consider conducting a Gut Challenge Assessment during exercise. The underlying cause and exacerbating factors to gastrointestinal symptoms can be identified and managed following such an intervention. Furthermore, carbohydrate requirements (i.e., quantity and quality) for endurance exercise can be more accurately determined in this assessment, reducing unnecessary stress on the gut during exercise due to overfeeding .
- To date, there is insufficient evidence that dietary supplements (i.e., probiotics, antioxidants, glutamine, L-arginine, L-citrulline, and bovine colostrum) provides any substantial beneficial effects (albeit, some negative effects have been reported) in respect to preventing or managing exercise-associated gut disturbances or symptoms in response to exercise in those suffering from IBS, so intake is not justified [1,4].
Individuals interested in conducting a hydration or gut challenge assessment should enquire at the Monash University, BASE Nutrition & Exercise Clinic;
Telephone: +61 3 9902 4270
 Costa, R.J.S., Snipe, R., Kitic, C., Gibson, P., (2017). Systematic review: Exercise-induced gastrointestinal syndrome- Implication for health and disease. Alim Therap Pharmacol 46(3):246-265.
 Miall, A., Khoo, A., Rauch, C., Snipe, R., Camões-Costa, V., Gibson, P., Costa, R.J.S., (2017). Two weeks of repetitive gut-challenge reduces exercise associated gastrointestinal symptoms and malabsorption. Scand J Med Sci Sports (In press).
 Costa, R.J.S., Miall, A., Khoo, A., Rauch, C., Snipe, R., Camões-Costa, V., Gibson, P., (2017). Gut-training: The impact of two weeks repetitive gut-challenge during exercise on gastrointestinal status, glucose availability, fuel kinetics, and running performance. Appl.Physiol.Nutri.Metab., 42(5):547-557. Gill, S.K., Allerton, D.M., Ansley-Robson, P., Hemming, K., Cox, M., & Costa, R.J.S., (2016). Does Acute High Dose Probiotic Supplementation Containing Lactobacillus casei Attenuate Exertional-Heat Stress Induced Endotoxaemia and Cytokinaemia? Int.J.Sports.Nutr.Exerc.Metab., 26, 268 -275.