Q. I've had stomach issues when racing. I'm about to do an Ironman and am considering taking Imodium. Is this a bad idea?
A. No. Between 20 and 40 per cent of all serious runners experience bowel problems when running.
Anxiety and mechanical forces probably play a part, as does gravity - some research suggests that people participating at similar intensities in sports in which body weight is supported (such as cycling or swimming) suffer far less from this problem.
During a serious run, the blood supply to the gut is reduced because blood is diverted to other parts of the body. The reduction is low (about five per cent) but even this can affect the bowels. There is also an increase in peristalsis - the muscular contractions of the bowel - especially if you're anxious.
Pre-race dietary preparation can affect some runners, so pasta loading or a high- carb diet can be upsetting to people who are sensitive to these types of dietary changes.
Try altering your pre-race dietary regimen to see if this helps, and take it easy with high-fibre foods - they take a long time to digest and can also absorb a lot of water. Also, try to allow about three hours between your last food and starting your race.
Make sure you are well hydrated at the start of a run - dehydration will affect your performance and can trigger bowel symptoms such as cramps and diarrhoea.
Avoid caffeine for 24 hours before a race because this can irritate the gut, and consider changing your sports drink; highly concentrated sugar solutions affect some runners. Taking an Imodium capsule about 15 minutes before the start of your race should cause no problems.
Dr Roger Henderson
Dr Roger Henderson qualified from St Bartholomew's Hospital in 1985 and became a GP in 1990. He is now the senior partner in a general practice and is medical columnist for the Sunday Times and the website NetDoctor. He has a keen interest in sports medicine and has run several marathons. He believes
in the restorative powers of a glass of wine and says that exercise should be enjoyable. Go to doctorhenderson.co.uk