Forum user Iceman writes: I’ve been running for many years. I run almost every day, I’ve done marathons and ultras.

Up until recently, I’ve had an iron stomach. I could eat a bowl of oatmeal with raisins, followed by ice cream the night before, washing it all down with a bottle of Metamucil, and get up the next morning for a 20 mile run with no problems.

These days, however, I get about 8 miles before I feel the urge to poop. I can usually make it about two more miles before I absolutely have to stop and go. Lately, I’ve been planning my routes so that I pass public restrooms at about this point, and I carry tissue with me.

However, today, my timing was off. I actually made it a bit farther than I thought, which was bad because I was on a city street, but it was early enough that nothing was open, so I couldn’t duck into a McD’s or a fancy restaurant. I found myself crawling into a dumpster to make the magic happen.

Now, I feel REALLY, REALLY guilty about it. I’m thinking about going back tonight when it’s dark with some kitty litter, water, bleach, and a shovel to clean up after myself.

I have two questions: Any reasons for the sudden change in my intestinal personality? And should I go back and clean up after myself, or am I overreacting?

Runner’s trots or runner’s diarrhea is a relatively common problem for runners and often requires timing your workouts to avoid having to “go on the run.” This is one of those “secret” personal problems runners seldom talk about with each other or their physicians. It happens to both world-class elite runners and ordinary fitness runners. I have witnessed the problem firsthand in several race medical tents, and even on a televised international marathon.

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For some unknown reason, physical activity like running can activate the large bowel resulting in the need to evacuate. This is not a problem if your route is peppered with accessible toilets, but becomes a personal emergency when facilities are not available. Runners with a history of this problem often learn to manage the problem by timing their runs to their bowel habits. It is the intermittent and unexpected episode that sets a runner up for the embarrassing situation you have described.

A once in a lifetime episode may just be bad luck, but if this is a recurring problem, you want to a search for a cause. There is a gastrocolic reflex in humans that is quite strong in babies and tends to be reduced or extinguished in adults. The gastrocolic reflex is simply described as “fill the stomach, empty the colon.” It is possible that running could trigger this reflex, so not eating within two to three hours of your run may help. Running-associated changes in gut blood flow may also contribute to the problem of increased gut motility or peristalsis.

A food sensitivity to dairy products (lactose intolerance) or a gluten sensitivity could also be a cause, and caffeine or other stimulants might activate bowel contractions. Try a dairy or gluten elimination diet for 2-8 weeks, then reintroduce it to see if you can uncover a problem.

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Your gut may also have trouble with high fiber or fatty foods. If so, you may need to avoid those foods before your runs. It may also help if you time that Metamucil shake to the meal after your run rather than at bedtime.

If you know how quickly food travels through your gut after a meal, you can sometimes avoid eating troublesome foods when they are likely to make trouble during your planned runs (especially your long runs).

You can check your gut transit time by eating corn or other foods with husks or skins that are not digested in the gut, or eating beets that pass a red color in your stool.

There is a lot of research being done on the gut biome, and maybe we will better understand the causes of runner’s trots as this research unfolds. If you have recently been on antibiotics, your gut biome may be adversely affected—so taking a probiotic may help the problem.

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If the “trots” have become a frequent problem for you, consider carrying an “emergency toilet” pack with a plastic bag that you can seal and some tissues or soft wipes. You can then carry your “deposit” home and dispose of it. I would refrain from climbing into a dumpster again. You can never tell what is in or has been in the receptacle; a cut or scrape may lead to a nasty infection.

Most of my patients with this malady learn to time their runs to their gut and develop running routes with accessible toilets.

If these strategies do not help, you should see your physician, especially if you are feeling ill, losing weight, getting more easily fatigued, notice blood in your stools, or have continuous diarrhea away from your runs.

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Get answers to questions on health, injuries and sports medicine from runner-friendly physician William Roberts, M.D. If you have a question for the Sports Doc, please ask it on our Health & Injuries forum.