Are You Training Your Gut ?


10 performance tips for the endurance athlete

From Fitness Trainer March/April

Athletes tend to do a good job of training their muscles, heart and lungs. But some of them (particularly endurance athletes and those in running sports) commonly fail to train their gut.

As one marathoner reported, “I was so afraid of getting diarrhea during long training runs that I did not eat or drink anything beforehand. I really struggled after 14 miles…” A high school soccer player admitted, “I’m so afraid I’ll throw up if I run with food in my stomach.” He ate only a light lunch at 11 a.m. and then practiced on fumes at 3:30 p.m. No wonder he had a disappointing season.

An estimated 30-50% of endurance athletes (including up to 90% of distance runners) have experienced gastrointestinal (GI) issues during and after hard exercise.

They fear bloat, gas, nausea, stomach cramps/pain, side stitch, diarrhea, vomiting, and urge to defecate. These issues arise during long bouts of exercise because blood flow to the gut is reduced for an extended period of time. When combined with dehydration, elevated body temperature, and high levels of stress hormones; normal intestinal function can abruptly end.

Ready, Set, Digest

If you have a client with a finicky GI tract, restricting diet before and during exercise will not solve the problem. You want them to learn how to train their gut to accommodate performance enhancing carbs and water. That way, they can train better—hence compete better—without stressing about undesired pit stops.

Thankfully, the gut is trainable. Competitive eaters have proven this point. Google Nathans’ Hot Dog Eating Competition and watch the video of a champ who stuffed 72 hotdogs into his stomach in 10 minutes. Clearly, he had to train his gut to be able to complete that task.

Competitive eating is unlikely their goal, but they may want to be competitive in their sport. That means they need to fuel wisely in order to perform optimally. While some “ketoathletes” choose to train their bodies to rely on fat for fuel (fat is less likely to cause GI distress), training the gut is a far easier alternative for most of us.

The following tips can help them exercise with digestive peace.

The Bottom Line

  • Train with relatively large volumes of fluid to get the stomach used to that volume.
  • Routinely eat carbohydrate-based foods before training sessions to increase the body’s ability to absorb and use the carbs.
  • During training, practice race-day fueling. Mimic what might be eaten before the actual competitive event, and tweak it until the right balance is found.
  • If they are concerned about diarrhea, in addition to preventing dehydration, limit fiber intake for a few days pre-event (fewer whole grains, fruits and veggies).
  • Reducing intake of onions, garlic, broccoli, apples, and sorbitol might help reduce GI issues during exercise.
  • Meet with a sports dietitian to help create a fueling plan that promotes intestinal peace and better performance.



Jeukendrup, A. Training the Gut for Athletes. Sports Med 2017; 47 (Supple 1): S101-S110

Prado de Oliveira E., Burine, R, Jeukendrup A. Gastrointestinal Complaints During Exercise; Prevalence, Etiology and Nutritional Recommendations. Sports Med 2014 (Supple 1): S79-S85


Nancy Clark

Sports nutritionist Nancy Clark MS RD CSSD has a private practice in the Boston-area

(Newton; 617-795- 1875), where she helps both fitness exercisers and competitive athletes create winning food plans. Her best-selling Sports Nutrition Guidebook, and food guides for marathoners, cyclists and soccer are available at

For workshops, see