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 / Updated  / Source: TODAY

Halfway through the 2003 Los Angeles Marathon, Emma Diego was on pace to clock a 3:40 — her Boston qualifying time — when painful stomach cramps forced her to make three detours into Porta Potties. She finished in 3:48. The total length of her lavatory layovers? Eight minutes.Diego's experience is, unfortunately, not uncommon. Studies suggest that as many as 60 percent of runners experience varying degrees of nausea and unpleasant stomach issues during or following a run. Gastrointestinal (GI) issues can make finishing a workout painful, or worse, they can impair performance. The problems are said to be caused, in part, because blood is diverted from the GI tract to the muscles during exercise. The diversion of blood can cause cramping and limits the body's ability to absorb fluids, potentially leading to dehydration. "Stops at the Port-a-John can also accelerate dehydration, which can end a race," says Bobby McGee, a distance-running coach in Colorado and running expert for USA Triathlon.The main culprit of stomach distress, however, is running itself. When you ride a bike, blood is also diverted from the gut, but cyclists report half the number of GI problems as runners. That's because running has twice the force of impact. "All the pounding jostles the GI tract," says Stephen Simons, M.D., a sports-medicine physician at St. Joseph Regional Medical Center in South Bend, Indiana. Which, in turn, speeds up the need for a pit stop.But why do some runners suffer and others don't? Because the amount of bacteria in the stomach, digestion time, and even hormone and stress levels affect digestion and vary from person to person. And because running compounds preexisting conditions like lactose intolerance and irritable bowel syndrome, says Dr. Simons. Some runners experience difficulty only during speedwork and races (at higher intensities, more blood is diverted, increasing the likelihood of GI distress). The solution is to experiment with your diet the day before workouts that give you trouble. "Test different foods," says McGee. "You'll find what works for you."

Change for GoodIn the late 1980s, gastrointestinal specialist Mervyn Danilewitz reported curing a number of runners' stomach ailments by having them eliminate dairy 24 hours before running. Milk, cheese, and ice cream can trigger stomach pain because they contain lactose, a sugar that's hard for some people to digest. If you just can't skip your glass of milk, try soy, rice, or almond milks, which generally don't contain lactose. Or choose acidophilus milk and yogurts with "live and active cultures" (look for the seal). These products have added bacteria that help break down lactose.Another option is to reduce your fiber intake — its indigestibility cleans out your system, but it also increases the risk for GI trouble. "When fiber gets low in the tract, bacteria feast on it, producing gas and sometimes cramping," says Bob Seebohar, R.D., director of sports nutrition at the University of Florida. Replace high-fiber fruits and veggies like pears and green peas with lower-fiber cantaloupe and tomatoes (see "Easy to Take," above). And save the bran cereals and other high-fiber foods for after your run.Certain sweeteners can also lead to GI trouble. Check the ingredients in your energy bar for anything ending in "ol" — sorbitol, mannitol, and so on — and avoid gels that list fructose as the first sugar on the ingredient list. "These sweeteners can cause GI trouble," says Seebohar. And take gels slowly. "Suck a little goo, sip some water, and then swallow," says Seebohar. "Otherwise, the gel could just sit in your stomach."Other solutions include avoiding cruciferous vegetables, like broccoli, cauliflower, and cabbage; they contain raffinose, a gas-inducing compound also found in — you guessed it — beans. And limit hard-to-digest foods like protein and fats. The night before or the morning of a run, aim for a meal that is 80 percent carbs, 10 percent protein, and 10 percent fat.Finally, watch the timing of your meals. Allow three hours between big meals and your run; eat dinner at least two hours before bed. And, of course, try to empty your system before a run. Coffee and tea can help move things along, but limit your intake to one cup, says Seebohar: "Caffeine can trigger GI complaints when taken in large quantities." Runners with frequent heartburn should skip caffeine altogether because it can increase acid in the stomach.

Most of all, don't let GI trouble keep you from your run. "As you get more fit, the muscles divert less blood, and there's more for the stomach," Dr. Simons says. "The effect on the gut improves." And so does your running.