Food, endurance exercise and gut health

Do certain foods cause you gastrointestinal issues when exercising? Would changing what you eat reduce the symptoms? What else should you do?

If you’ve been following my page for a while, you’ll know that I’m a bit of a research nerd 🤓! I recently took a short course through Monash University aimed at helping health professionals work with their clients to help manage gastrointestinal issues associated with exercise. The course helped deepen my understanding of gut health and how food and exercise can affect the gastrointestinal tract.

So what do we know? A recent Monash University review has found that people who exercise for more than 2 hours may be prone to acute or chronic gut issues and as duration and intensity of exercise increased so too did the 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 health complications, and exacerbate already established conditions including irritable bowel syndrome (IBS).

However we also know that for people with IBS low to moderate activity (walking or running three times per week) may be beneficial for symptom management and improving quality of life. The gut disturbances occur once exercise is for two hours or more, especially for running (compared to cycling) and in hot weather.

So what can you do, if you love long distance running, live somewhere warm (hello summer in Sydney!) and get an upset gut? Luckily there are some practical solutions:

  • ensure optimal hydration before exercise and maintain hydration during exercise. You might consider doing a hydration assessment to measure your “sweat rate” to determine a hydration schedule

  • consider lowering the FODMAPs content of the diet prior to periods of heavy training or racing.

  • Many ‘sport foods’ (e.g., drinks, gels or bars) contain fructose and sorbitol which can be an issue for people that malabsorb these sugars. Use glucose/dextrose/maltodextrin based products and consume small amounts regularly throughout exercise. I’ve written more about low FODMAP sports supplements here

  • You can “train your gut” to get used to fuelling during exercise so practice your race nutrition

  • Avoid non-steroidal anti-inflammatory drugs (e.g., aspirin and ibuprofen) around training and competition schedules. This was one major take-away I took from the course, learning how NSAIDs increase intestinal permeability so the tight junctions of the intestinal wall become loose, allowing bacteria and toxins to enter the bloodstream.

  • Avoid exercising in hot conditions (e.g., ≥30°C), so go early or late if you can, and if you need to exercise in the heat slow your intensity 

  • So far there is insufficient evidence that dietary supplements such as probiotics, antioxidants, glutamine, L-arginine, L-citrulline, or bovine colostrum provide any beneficial effects (and some cause negative effects!) in respect to preventing exercise-associated gut symptoms, so save your money on these.

Are you training for an endurance event?  Did you know that using a scientific approach to nutrition in a marathon takes, on average, nearly 11 minutes OFF an amateur runner's finish time?  My 8 week Endurance Nutrition program focuses on supporting your marathon training with making nutritious food choices a priority so that you can get to the start line feeling great.  On race day you will be armed with well trialled strategies that work for you and will help you run your best fuelled marathon, half marathon or triathlon.