Gastrointestinal Function and Exercise

The gastrointestinal (GI) system consists of all those organs involved in the digestion of food, as well as its transport into the bloodstream and the elimination of waste products from the body. The GI system consists of the esophagus, stomach, small intestine, large intestine, rectum, and anus, along with organs associated with this system, such as the liver, gallbladder, and pancreas. Exercise can have a variety of effects on the way in which the GI system functions.

Nutrients in the foods that a person eats are used by the body to provide energy for body functions and the raw materials of which new body parts are made. The GI system breaks food down into its components parts, many of which consist of those nutrients. As nutrients, such as glucose (“blood sugar” and amino acids) are released from digested foods, they pass through the walls of the GI system and into the bloodstream, within which they are carried to cells throughout the body. Portions of food that are digested remain in the GI system and are excreted from the body through the excretory tract, consisting of the rectum and anus. Malfunctions of the GI system can result in a number of medical problems, ranging from mild to severe. These problems include chest pain, heartburn, belching, abdominal cramps, constipation, diarrhea, nausea, vomiting, gastroesophageal reflux disorder (GERD), dyspesia, gastritis, irritable bowel syndrome (IBS), gastrointestinal bleeding, Crohn's disease, ulcerative colitis, and colon cancer.

The single most important factor determining the effect of exercise on the GI system is intensity of the exercise. Moderate exercise appears to have a number of benefits for GI function, including a more efficient digestive process and a healthier GI system in general, as well as offering protection against a number of common GI disorders, such as constipation, diverticular disease, cholelithiasis, and colon cancer. By contrast, more strenuous exercise tends to have deleterious effects on a person's GI system, resulting in a variety of conditions that include chest pain, heartburn, belching, abdominal cramps, constipation, diarrhea, nausea, vomiting, GERD, dyspesia, and gastritis.

Most studies show that 20%–70% of elite athletes report some type of GI malfunction. Female athletes experience relatively more problems than do male athletes, and GI problems tend to be more common among younger athletes than older athletes. GI problems tend to be more common in sports that involve vigorous, abrupt movements (such as running) than in sports that use smooth motions (such as swimming). One study found that the frequency of GI problems was almost twice as high for running as for other sports, and up to three times as common among elite athletes compared to recreational athletes. That study also found that the level of GI malfunction was such that it prevented anywhere from a quarter to a half of all elite athletes from participating in formal competition at one point or another.

The most common types of GI malfunction associated with exercise are nausea, vomiting, GERD, gastric pain, bloating, belching, constipation, diarrhea, rectal blood loss, flatulence, urge to defecate, abdominal cramps, and fecal incontinence.

The GI problems associated with intense exercise appear to be relatively easily controlled, as discontinuation of that type of exercise generally results in decrease or termination of the symptoms. For professional athletes, of course, that option is generally not available, and the symptoms of GI malfunction have to be dealt with symptomatically.

David E. Newton, AB, MA EdD