Intestinal Distress and Urgent "Pit Stops"

author : Nancy Clark
comments : 3

Endurance run training can mean unpleasant digestive problems for triathletes.

While some runners have cast iron stomachs and few concerns about what and when they eat before they exercise, others live in fear of pre-exercise fuel contributing to undesired pit stops during their workouts. Be it stomach rumbling, a need to urinate or defecate, reflux, nausea, heartburn, or side stitch, how to prevent intestinal distress is a topic of interest to athletes with finnicky guts. Here are tips to help you fuel well before and during runs, races and workouts while reducing the risk of gastro-intestinal (GI) distress. For more in-depth information, you might want to read The Athlete’s Gut by Patrick Wilson or listen to this podcast.

  • Stay calm. Being anxious about intestinal issues can exacerbate the problem. Think positive. Trust that your gut is adaptable and trainable. Record what, when, and how much you eat, as well as the duration and intensity of your runs, and use that data to help you figure out what foods and fluids settle best. Building body trust can reduce anxiety—and that can help reduce GI issues. That said, pre-competition nerves can affect any runner, regardless of GI hardiness!

  • Triathletes are more likely to suffer GI issues while running versus cycling or swimming. With running comes intestinal jostling; the longer the intestines are jostled, the higher the risk of upset. Ultra-runners know this too well…

  • If you experience gut issues every day—even when you are not exercising, you want to talk with a GI doctor. Celiac disease, Crohn’s, ulcerative colitis, and blood in your stool need to get checked out now! They are serious issues and differ from exercise-induced GI problems.

  • The higher the intensity of your runs, the higher the risk of intestinal distress. Add heat and anxiety to a hard workout, and many runners experience transit trouble. During hard runs, blood flow diverts away from the gut to transport oxygen and glucose to the working muscles and carry away carbon dioxide and waste products.

  • Low intensity runs are less problematic. The GI tract gets adequate blood flow, can function relatively normally and digests, absorbs, and metabolizes pre-run fuel. Runners tend to have fewer GI issues on easy training days that offer better blood flow to the intestines, as well as lower body temperature and less anxiety.

  • Carbohydrate is the fuel that is easiest-to-digest before and during long runs. Carbohydrate gets broken down into simple sugars in the stomach, then absorbed into the bloodstream from the small intestine. Specific transporters carry each sugar molecule (such as glucose or fructose) across the intestinal wall. Hence, consuming a variety of carb-based fuels helps minimize a “backlog” if all the transporters for, let’s say, fructose get called into action.

  • With training, the body creates more transporters to alleviate any backlog. That’s one reason why you want to practice pre-run fueling during training sessions. Your body gets the chance to activate specific transporters. The foods and fluids you consume before and during training should be the same ones you’ll use for the race. Some popular carb-based snacks for before and during long runs include fruits (banana, applesauce), vegetables (boiled potato, roasted carrots), and grains (sticky rice balls, pretzels, pita)—as well as commercial sports foods (sport drinks, gels, chomps).

  • Runners who experience gas and bloat want to familiarize themselves with FODMAPs —Fermentable (i.e., gas-producing) Oligo-, Di-, Mono-saccharides And Polyols. These are sugars and fibers that some people have trouble digesting. Commonly eaten sport foods high in FODMAPs include milk (apart from lactose-free milk), bread, pasta, onions, garlic, beans, lentils, hummus, apples, and honey.

    By choosing a low FODMAP menu for a few days before race day, a runner might be able to reduce, if not avoid, digestive issues. (Of course, you want to first experiment during training to be sure the low FODMAP pre-race foods settle well.) Low FODMAP foods include bananas, grapes, cantaloupe, potato, rice, quinoa, cheddar cheese, Parmesan cheese, and maple syrup. Some low FODMAP commercial sport fuels include (but are not limited to) Skratch Labs Hydration mix, peanut butter and orange Hammer Gels, Gatorade thirst quencher, Gu Chews, strawberry lemonade Infinit Essential Hydration, and Tailwinds Endurance Fuel. For more information on FODMAPS, refer to

  • Fatty foods (butter, cheese, nuts) tend to slowly leave the stomach and are metabolized slower than carb-rich foods. If you will be running for less than two hours, think twice before reaching for a handful of nuts or a chunk of cheese for a quick fix as you dash out the door. A banana or slice of toast will digest quicker and be more available for fuel.

  • Eating fatty foods on a regular basis can speed-up gastric emptying a bit, but you won’t burn much pre-run dietary fat during your workout unless you are a marathoner or ultra-runner who will be exercising for more than 3 hours. In that case, a bagel with nut butter or cheese will offer long-lasting fuel.

  • Some runners chronically under-eat. This includes those trying to lose weight and others with anorexia. Under-eating can impair GI function; the gut slows down with inadequate fuel. Delayed gastric emptying means food stays longer in the stomach and can feel “heavy” during runs (as well as is less available for fuel). Slowed intestinal motility easily leads to constipation, a common problem among under-eaters.

  • Highly active runners, such as those doing double workouts and ultra-runners, need to consume a large volume of food to support their performance. If they are eating primarily “healthy” foods, they can easily consume a lot of fiber —and that can easily contribute to rapid transit. Runners needing a high calorie diet often benefit from including some so-called less-healthy foods (such as white bread, white rice, cookies, candy) for low-fiber muscle-fuel.

  • Given each runner has a unique GI tract, be sure to experiment during training to learn what works best for you and your gut. Eat wisely and enjoy miles of smiles.

Sports nutritionist Nancy Clark, MS, RD counsels both casual and competitive athletes in the Boston-area (Newton, 617-795-1875). Her best-selling Nancy Clark’s Sports Nutrition Guidebook (6th edition, 2019) can help you eat to win. For more information, visit


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date: July 31, 2020

Nancy Clark

Nancy Clark, MS, RD, an internationally known sports nutritionist and nutrition author, is a registered dietitian (RD) who specializes in nutrition for exercise, health and the nutritional management of eating disorders.

avatarNancy Clark

Nancy Clark, MS, RD, an internationally known sports nutritionist and nutrition author, is a registered dietitian (RD) who specializes in nutrition for exercise, health and the nutritional management of eating disorders.

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