I frequently hear from triathletes who suffer from gastrointestinal symptoms associated with racing, predominantly during the run. These include gastroesophageal reflux, or heartburn; delayed gastric emptying; intestinal bloating and flatulence; and diarrhea. Although they’re not truly dangerous, these symptoms often impair performance and are more pronounced during longer races and in those who become dehydrated.
Gastroesophageal reflux (GER): The esophagus is a muscular tube with a sphincter at the lower end. Normally, contractions of the muscles in the wall of the esophagus ensure that whatever you swallow moves down toward the stomach, while the sphincter then prevents the contents of the stomach from coming back up. During exercise, both of these processes can be impaired by an increase in intra-abdominal pressure that can result in the reflux of acidic stomach contents into the esophagus.
There are few effective remedies for this, although one important strategy is to avoid the things that are known to relax the lower esophageal sphincter. These include caffeine, alcohol and smoking. Taking chewable antacids or over-the-counter acid-reducing medication may provide some relief. For the most part, exercise-induced GER causes only mild, self-limited symptoms and is not known to cause any long-term problems.
Delayed gastric emptying (DGE): Most triathletes understand the importance of ingesting an adequate amount of fluids, electrolytes and energy sources during prolonged periods of exercise. Unfortunately, not everything that is ingested passes out of the stomach in a timely fashion, an issue that is more pronounced at higher levels of exertion. This results in a feeling of fullness and bloating and may lead to nausea and vomiting. More importantly, dehydration can ensue when less fluid is delivered to the intestines. As athletes become dehydrated, they experience a further decrease in gastric emptying that can accelerate dehydration.
DGE can have a significant negative impact on athletic performance. Unfortunately, there is no way to completely prevent this nor is there any rapidly effective treatment. The best preventive measure is to ingest a balance of high- and low-energy fluids (i.e., a mixture of water and sports drinks) to keep the concentration of sugars from getting too high.
Once DGE becomes apparent, the only viable remedy is to decrease the effort of exertion to a level below 70 percent of aerobic capacity and avoid high-carb sports drinks in favor of plain water. This should restore a more normal rate of gastric emptying. Once the symptoms have abated, athletes can try raising their level of exertion, paying careful attention to fluid intake.
Intestinal bloating and flatulence: There are two reasons for this: swallowing air and ingesting a high concentration of simple sugars. Air ingestion occurs most commonly while swimming. Once in the stomach, air can pass into the intestines. Having significant quantities of air in the bowels causes uncomfortable bloating and cramping. The best way to avoid this problem is to encourage belching to expel any air that you have ingested while swimming.
Your stomach might not completely absorb simple sugars in high concentrations. This too can cause uncomfortable bloating and cramping. The best way to avoid this problem is to minimize the concentration and amount of simple sugars ingested.
Diarrhea: A final common problem that many endurance athletes encounter is diarrhea. The most common causes of this are related to fluid shifts and decreased absorption.
Drinking large amounts of fluids that contain high concentrations of simple sugars may cause fluid to be drawn from the bloodstream into the intestines. This speeds up intestinal transit, resulting in possibly severe diarrhea that can lead to dehydration. Once again, the best preventive measure is to ingest a lower volume of simple-sugar-containing fluids and increase water intake.
Jeffrey Sankoff, MD, is a two-time Ironman triathlete and ER physician at the University of Colorado Health Sciences Center in Denver, Colo.