It has been estimated that 30-50% of athletes experience gastrointestinal discomfort during endurance activities, and in one study of long distance triathletes, nearly 93% endorsed gut symptoms. Symptoms can range from an annoyance to a severity that pulls you out of the race (second 0:47). In this post we will review the major causes of gut discomfort in endurance athletes and what you can do to prevent them.
Decreased blood flow to the Gut
Reduced blood flow to the gut is a normal response to exercise because blood gets diverted to the muscles. Gut issues arise when exercise becomes prolonged, intensity increases, and/or the athlete is dehydrated. These variables compound the effects of decreased blood flow to the gut causing discomfort. Unless, you're doing a recovery workout you will likely experience one of these variables during your training and racing.
Stay hydrated. The science behind hydration and exercise can be barely summed up in a doctoral thesis let alone a blog post but here is a good rule of thumb to get you started:
If less than 2 hours you can usually get by with just water, but only if you go in well fed and hydrated, and the intensity remains medium to low.
Take in 250-1000 mg of sodium per hour in the form of food or drink
Diminished blood flow to the gut can make small nutritional differences a big problem while exercising. Fiber, fat, protein, and fructose have all been associated with increased gut discomfort in endurance athletes. Regardless, of what you use for nutrition there is one thing that will screw it all up: dehydration. Hydration drives nutrition! Without adequate fluids the food you eat will sit in your gut like a giant burrito.
Avoid high fructose foods. Foods, gels, and drinks with a combination of carbohydrates appear to be better tolerated.
Avoid high fiber foods during exercise
Eating while exercising should be followed by fluids - Hydration drives nutrition!
Don't drink your calories – Separate your hydration from your nutrition.
Avoid products with sorbitol. Many of the gels, chews, and electrolyte products out there contain this sweetener, which can cause diarrhea.
The repetitive jostling of your gut while running is thought to contribute to GI upset, diarrhea, and flatulence. Issues with reflux can also arise with poor bike fit. Being in a tucked, aero position puts extra pressure on the abdomen potentially leading to heartburn.
Runners can work on improving their vertical oscillatory movement (ie, how much you move up and down with relation to the ground while running). Less oscillation not only makes you a more efficient runner, but will be less jarring on your gut. Having your bike professionally fit will help reduce issues with reflux.
Non-Steroidal Anti-Inflammatory drugs (NSAIDS)
Drugs like ibuprofen, Aleve, and aspirin increase gut permeability (“leaky gut”) causing discomfort. Use of these drugs can also contribute to stomach and duodenal ulcers. Studies have also shown that NSAIDs can impair performance as well.
Don't take them before or during a race – stick with Tylenol.
Take Home Tips:
Hydration drives nutrition!
Don't drink your calories – separate your hydration from your nutrition.
Don't use NSAIDs
Don't wait until race day to figure out what works best for you.
You need to know how much water, sodium, and carbohydrates you should take in for every hour your training or racing. The complexity of this only increases with the extremes of temperature. But the better you can dial in your nutrition and hydration the better you will perform and the fewer gut issues you will experience.