Gastrointestinal (GI) problems are a common concern of athletes during intense endurance exercise, in particular during races.  In most studies the incidence of GI symptoms has been documented as being between 30-50%.  Ultimately these symptoms can impair performance and possibly prevent athletes from winning or even finishing a race.  The causes of GI problems during exercise are diverse, but among others include unaccustomed or inappropriate food and fluid intake.  It is therefore vital for athletes to carefully select and test their food intake before race day.
It has been demonstrated that exercise at high intensities leads to a redistribution of blood flow such that the priority becomes to nourish the exercising muscle.  This leads to a reduced blood flow into the gut of up to 80%.  It has been suggested that alongside changes in nervous activity and altered hormonal responses during exercise this can lead to the development of GI symptoms. The exact causes of GI symptoms, however, are incompletely understood. On top of these exercise induced GI problems; race nutrition can exaggerate or cause a number of GI problems.

What can athletes do to prevent GI problems?

• Testing of food and drink intake during intense training or less important races is vital.
• Training of fluid intake especially during running can reduce discomfort.
• Sufficient fluid intake before and during the race (euhydration).
• Avoid fiber rich foods (e.g. beans, bran, fruits, seeded or wholemeal bread) intake in the days before the race and during the race.
• Avoid high fat foods in the days before the race and during the race.
• Allow sufficient time (> 3 hours) to digest the last meal.
• Test your tolerance of lactose and if sensible avoid diary products before the race.
• Caution with NSAIDs and aspirin.
• Limit use of caffeine on race day.
• Stress management in order to keep psychological stress on race day low
• Adapt intensity to allow normal gut function

Protocol for those with GI bleeding presenting for medical evaluation:

• Elevate legs 12 inches above their core
• Ask about regular NSAIDS use and/or on course use
• Hematemesis, coffee grounds or blood in stool
• inquire about cardiac history and risk factors
• Check I-stat sodium
• Consider IV fluids if sodium > 135 mEq/L and signs of hypovolemia
• Arrange transport to the ED if more than 1 bloody bowel movement or hematemesis