20 to 50% of athletes complain of gastrointestinal problems while running, especially during hard training sessions and races. Women, novices and younger athletes are most affected.
It is not completely clear what is happening, but it is likely that during intense exercise your digestion gets hampered, because most of the blood is diverted from your bowels to your working muscles. During running, bouncing and compression of the gut can aggravate the situation.
If that is true, the best thing that you can do is to reduce your bowels’ workload:
- Eat your last meal at least 2 hours before the race and avoid fatty and high-fibre food. Consider having a liquid meal, such as a meal replacement drink, as that is quicker and easier to digest.
- Keep hydrated during the run, but do not overdo it: drink to your thirst. Sport drinks are much easier to digest than juices or soft drinks.
- Some people cannot digest milk and dairy products during exercise, even though they can at rest. Experiment with avoiding dairy products for 24 to 48 hours before the race.
- Caffeine can give you a boost during a race, but sometimes it leads to gastrointestinal symptoms. Try out how it works for you during training sessions.
Do not forget that exercise is good for your bowels: physically active people reduce their risk of bowel cancer by up to 50% and suffer less from gallstones or diverticular disease. Some researchers have even shown that runners are less likely to be constipated than the general population. Even so, it is not because you are a really fit athlete that you are immune from disease: contact your doctor if you have any concerns, if your stool habits change or if you see blood in it.
C Riddoch and T Trinick.Gastrointestinal disturbances in marathon runners. Br J Sports Med. 1988; 22(2): 71–74.
RW ter Steege and JJ Kolkman. Review article: the pathophysiology and management of gastrointestinal symptoms during physical exercise, and the role of splanchnic blood flow. Aliment Pharmacol Ther 2012; 35(5):516-28.