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Could Your GI Problems Actually Be a Food Intolerance?

Learn what factors could be contributing to your food intolerance symptoms and troubleshoot your GI issues to start performing better.

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It’s very common to see athletes eating gluten-free, avoiding dairy, and eliminating grains or other foods—and not because they have celiac disease or an allergy, but because they perceive that their performance improves with these restrictions. Sometimes this is a short-term measure focused on particular competitive goals, but in other cases these choices are lifestyle changes rooted in improved well-being and reduced GI problems.

Although there is no evidence to suggest that the prevalence of food intolerances in the athletic population is any different from that of the general population, athletes may be more likely to either identify or be diagnosed with a food intolerance. For an elite athlete, improvements in mere seconds, milliseconds, and percentages add up to a significant difference in overall performance, so identifying the cause of anything that reduces the capacity to compete, train, or recover is worth pursuing. Diet is paramount for everything, from the ability to recover from hard training to hand-eye coordination and quick reflexes to building a body best suited to the demands of a particular sport.

Athletes are more likely to recognize symptoms of food intolerance, largely because they are used to analyzing how they are physically performing and feeling, so they may also be more attuned to things going awry or being slightly off. Symptoms of food intolerance may also be more pronounced or frequent with the effects of exercise, prompting athletes to seek out a diagnosis or probable cause.

Furthermore, increasing permeability of the gut will also increase the risk of food intolerance. As the gut becomes more permeable, the body’s immune system is activated to deal with the invading foreign particles. There are three main ways in which the gut can be compromised during exercise: the physical and mental stress associated with intense training or race day nerves, the mechanical factors related to the motion or activity of exercise, and the dietary intake and medications that are often the mainstays of athletic populations.

Because these factors lead to the onset of food intolerance symptoms, we need to differentiate between the possible causes: a food intolerance that is exacerbated by exercise; a food intolerance that is caused by exercise; and symptoms such as GI distress that may present themselves like food intolerance when they are actually related to the effects of exercise itself. For instance, too much fiber or a state of dehydration can cause GI distress during a workout. It has nothing to do with a food intolerance. Understanding how exercise impacts your gut will help you begin to determine whether you need to avoid certain foods altogether, limit your intake of a particular food prior to training, or simply change your fueling strategy.

How to Troubleshoot Your GI Issues

Issues Caused by Specific Foods and Fueling Strategies


Sensitivity to these particular carbohydrates can be increased above threshold tolerance levels due to the anxiety or stress associated with an event or even a disruption in your routine. If you are sensitive to FODMAPs, be aware of what you are eating in the 24–48 hours pre-race.


A common ingredient in sports foods, fructose is one of the FODMAPs that can cause GI problems for athletes. If the foods you are fueling with contain fructose, pay close attention to whether malabsorption or intolerance could be to blame.


This is often a transient intolerance that only presents during exercise. Take note of the timing and types of dairy you consume if lactose is pinpointed as the cause of your GI distress.


Athletes may have poor tolerance of this stimulant either because of increased gut motility or sensitivity. If caffeine or coffee is not identified as a trigger food at other times and only becomes problematic on competition day or before intense workouts, then you may need to experiment with timing or the amounts you consume if you don’t want to completely avoid it.

Other Food Intolerances

Underlying food intolerances can be exacerbated by exercise stress. Look for any other symptoms that may be present either during or after your workout/race.

Meal Timing

Eating meals too close to exercise can be a recipe for disaster because food volume increases pressure on the gut. Ideal timing will depend on numerous factors including type and intensity of exercise, volume of the meal or snack, and individual requirements and tolerance.

Excess Fat and Fiber

Too much fat or fiber can increase motility in the gut, essentially rushing things along too quickly through the GI tract, or they can place additional digestive stress on the GI system. Experiment to find the amount you can tolerate and the best timing.

Composition of Drinks/Foods

Gastric emptying and intestinal fluid absorption are reduced when the carbohydrate concentration of sports drinks, gels, bars, or other foods in the gut is excessive. Changes in fluid and sugar concentrations slow the rate of gastric emptying and increase the likelihood of GI symptoms.

Hydration Status

Dehydration can exacerbate GI symptoms and slow gastric emptying. Monitor your hydration by drinking to thirst, observing pre- and post-workout/race weights to help guide fluid needs, and noting urine color—it should be straw colored, not bright yellow or orange, but also not clear or very pale.

Issues Caused by Other Race-Day Situations


Pre-race nerves are inevitable, but being overly anxious is a hindrance to performance. To help control anxiety, try following a familiar routine, chatting with family or fellow racers, listening to music, or practicing visualization and calming techniques.

NSAIDs and Antibiotics

Both increase intestinal permeability and should be avoided pre-race. If you use NSAIDs and antibiotics, you can experience GI issues without the existence of a food intolerance.


Sports like cycling can put pressure on the abdomen, increasing the risk of upper GI issues. In cycling, to some extent bike fit can alleviate postural issues. In other sports, the balancing act between optimizing posture for GI comfort versus performance will tip either way depending on the level of the athlete and the demands of the race.

Vibration or Jarring of the Gut

This comes as a result of exercise, particularly sports that involve running and jumping. Friction and irritation can lead to diarrhea or stomach pain. Unfortunately, a jarring motion is unavoidable in many sports, so the solution is making things easy on your gut in other ways, such as practicing appropriate fueling, avoiding irritating foods, and staying hydrated.

Adapted from The Athlete’s Fix: A Program for Finding Your Best Foods for Performance and Health by Pip Taylor, with permission of VeloPress.