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Ask The Coach: How Do I Avoid GI Problems In A Marathon?

Matt Fitzgerald explains how to keep it all in check on race day.


Dear Matt,

I have run three marathons, and in each one I have experienced gastrointestinal issues that affected my performance. I’ve used the drinks and gels provided on the course. What’s strange is that I never have GI problems in my long training runs even though I use the same products. What am I doing wrong?


Reno, Nev.


Dear Meredith,

Your problem is not uncommon. A marathon subjects the body to a level of stress it never experiences in any workout. Consequently, the body sometimes experiences a bad reaction to physiological stress in a marathon that never crops up in training. Muscle cramping is one such reaction that is quite common, and gastrointestinal distress is another.

Unfortunately, some runners’ GI systems are more sensitive than others. It may not be possible for you to fuel your marathons as other runners do. Your goal should be to find the race fueling system that maximizes your performance, regardless of whether that system matches what your fellow runners do.

I think it’s safe to say that your current approach to marathon nutrition is not maximizing your performance. Your belief that the GI problems you’re experiencing during marathons are negatively affecting your performance is undoubtedly correct. The surest way to avoid nutrition-related GI problems during a marathon is, of course, to take in no nutrition at all. But you would probably perform even worse in a marathon in which you drank and ate nothing than you would in a marathon in which you fueled yourself like everyone else and suffered GI distress. So it’s probably best if you accept some risk of suffering GI issues by consuming something during your next marathon. But you’ll want to minimize that risk as much as you can.

How do you minimize the risk of suffering GI distress without “fasting” through the marathon? Here are three guidelines:

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Keep It Simple

The more types of nutrition you consume during a marathon, the more likely it is that you will consume something problematic, or that the combination of things you consume will become problematic in your stomach. Sports drinks are formulated to provide everything your body needs during running. I recommend that you consume a sports drink only — no gels, chews, bars, or supplemental water.

Go Light

No matter what you drink, you probably can’t get away with drinking as much as most runners can. That’s OK. Take comfort in knowing that Alberto Salazar ran a world-record 2:08 marathon back in the early 1980s without drinking anything. While taking in fluid and carbohydrate does enhance performance, it doesn’t make the life-and-death difference that sports drink makers would like you to believe. So just trust that something is better than nothing, and also know that too much is just as bad as nothing, and err on the side of conservatism in your rate of drinking during the marathon. Take only a small sip at each aid station, or skip every other aid station altogether.

Also be aware that the less you drink during some of your long training runs, the less negatively “going light” will affect you in the race. Therefore I suggest that you intentionally drink less than you could during every other training run. This will increase your muscles’ fat burning capacity so that you’re less likely to bonk during your next marathon even though you’re not drinking a lot.

RELATED: Effective Fueling Strategies

Drink What Your Tummy Likes

Generally speaking, the simpler and lighter the formulation of your sports drink, the less likely it is to upset your stomach. You’ll probably find that your tummy prefers sports drinks with lower concentrations of carbohydrate and without the “extra” ingredients some sports drinks have. If the sports drink offered on the course at your next marathon is too much for your tummy, you might be better off carrying your own — or choosing another marathon. It might sound crazy, but I actually choose my marathons in part based on the sports drink that is used on the course, because I want to drink what works best for my body and I don’t want to be weighed down by a bottle that I carry.



About The Author:

Matt Fitzgerald is the author of numerous books, including Racing Weight: How To Get Lean For Peak Performance (VeloPress, 2012). He is also a Training Intelligence Specialist for PEAR Sports. To learn more about Matt visit