Although they may not appear to be a frequent threat, gastrointestinal (GI) illnesses are the second most common cause of illness in sports, which has substantial impact on athletic performance. During exercise, GI system faces number of potential challenges that may increase the risk of GI symptom development and severity which includes reduction in blood flow, increased core temperature, potential alterations in GI physiology induced by feeding during exercise, hypoxia and dehydration and malabsorption of carbohydrates. Anxiety and stress experienced by endurance athletes, specially in the build-up to races, also increase GI symptom severity during the competition. A recent research reported the prevalence of GI symptoms in cyclists (4–7%), marathon runners (4–96%), ultra marathon runners (60–96%) and ironman triathletes (31–93%). These include upper GI symptoms (nausea, regurgitation, heartburn, belching, bloating, and abdominal cramps) and lower GI symptoms (abdominal pain, constipation, incomplete evacuation, diarrhoea and urge to defecate).

Infectious gastrointestinal diseases are commonly caused by bacteria, like Escherichia coli (enterotoxigenic), Salmonella, Shigella, and Vibrio. Viruses account for another part of the cases, with norovirus being the most common in adults and rotavirus in children. Symptoms can last less than 14 days in acute cases; but 14 to 30 days in persistent and more than 30 days in chronic cases. Traveler’s diarrhea is also another concern for athletes who travel to developing countries. Most cases are caused by bacteria, followed by viruses or parasites; nevertheless, coinfection may occur in up to 20% of cases. Management of acute gastroenteritis or diarrhea should focus primarily on two objectives: maintaining adequate hydration through replacement of lost fluids, preferably via the oral route and controlling symptoms. The use of antibiotics should be reserved for specific cases.

The athletes should follow some precautionary measures to reduce the disease load. They should avoid high-fiber foods in the day or even days before competition. The use of NSAIDs in the pre-race period should be discouraged, mainly for athletes with a history of gastrointestinal problems. Dehydration can exacerbate gastrointestinal symptoms, hence it is important to prevent dehydration and start the race (or training) well hydrated. It is essential to ingest carbohydrates with sufficient water or choose drinks with lower carbohydrate concentrations to prevent very high concentration and osmolality in the stomach. The athletes should make sure to experiment with the pre-race and race-day nutrition plan many times before the race day. This will reduce the chances of getting gastrointestinal symptoms. Another good option could be the  BRAT diet (bananas, rice, applesauce, toast)  given that in general they are easily available. This reduces weight loss due to fluid loss and facilitates return to training. Return to sports may be considered when the athlete is afebrile, adequately rehydrated, able to tolerate solid foods, and free of residual gastrointestinal symptoms, or at least 48 hours have passed since the last episode of diarrhea or vomiting.