Because I suffer from IBS (irritable bowel syndrome), it comes to no surprise that I commonly deal with GI distress when racing or training, in particular, on the run. Turns, out I'm not alone. Over 63% of athletes share this problem. Because I've had to deal with it on almost a daily basis, my stomach and I are much better prepared (trained?) on race day. Here are some tips:
Before Race Day:
Search for the Perfect Sports Drink
Gatorade is often a bad recipe for people with sensitive tummies. Search for a sports drink with maltodextrin instead of simple sugars. Avoid drinks with fructose as this has been proven to cause stomach upset. It seems that when you mix different chain length carbohydrates in the sports drink, you can absorb a higher concentration without GI upset (probably because there are more receptors available for the different sugars, as opposed to saturating a single receptor with only 1 sugar). Some people like Carbo Pro. I really love Infinit (http://www.infinitnutrition.com/) because you can customize the drink to your needs (# of calories, strength of taste, amino acids, protein, electrolytes, etc.).
Train Your Stomach During Training
You're not just training your muscles and heart; you're training your GI system as well. To toughen up to the jostling while continuing to absorb and digest food with less blood. Practice what you will eat and drink on race day. Practice the amount and frequency. Then, once you have it dialed in, all you have to do is repeat what you know works in training on race day. If you do have GI upset during training, keep going. It will give you really good practice for how to handle it on race day.
Eat Healthy Meals 48 Hours Prior to Race Day
Be very conscious about what you're putting in your bellies. That means no roadside Joe's Taco Shop stands. Avoid foods high in fiber and fat. Go for things high in carbohydrates (although be aware that too much of this can cause bloating). Things I like are chicken, fish, lean beef, white rice, cantaloupe, cereal, bread, nonfat yogurt, bananas, and other easily digestable foods. Go with foods you know have worked for you in the past. Eat light, frequent meals. Don't try to "carbo load" only 1-2 days in advance (proper carbo loading takes 1-2 weeks and doesn't involve over-eating).
Eat Breakfast (but not too big)
It's important to replace our glycogen stores that are used up while we sleep. However, a 300 calorie meal will suffice. Avoid the pancakes, bacon and eggs. Go for easily digestable foods like cereal with skim milk, bananas, or a bagel with peanut butter. If you're still having a hard time getting it down (most people with sensitive stomachs have a hard time with breakfast in the wee morning hours before a race--this is often due to excess acid), try liquid calories. If you're still having a hard time, pop an antacid like Pepcid or Tums to see if that helps.
During the Race:
Eat/Drink Little and Often
It's easier to absorb small amounts of liquids and foods frequently. Try to drink every 10 minutes or so. Most importantly, follow the plan you worked out in training.
Mix Solids with Liquids
In an Ironman, my stomach has a hard time with liquids all day. I feel better ingesting some solid foods at some point during race day. Sounds counterintuitive but it works. I think the solids (e.g. PB&J) help sop up the acid produced in the gut. For some, the opposite is true and they do better with only solids. You need to practice and experiment in training to get it all nailed down.
Always Drink Lots of Water with Solids and Salt
You need water to digest food. Popping a GU or salt tab without chasing it with 8 ounces of water is a recipe for stomach upset.
Keep Water Separate from Calories
GI distress can be a sign of dehydration. The last thing I want to do when my stomach hurts is drink nasty sports drink. I always keep my sports drink in a more concentrated form and chase it with a shot of water (in my aero bottle--I refill at aid stations). On the run, my cocentrated sports drink is in my fuel bottle and I chase it with a cup of water at aid stations. That way, I can customize as I go. If my tummy gets too full, I cut back on the sports drink and up the water. Or vice versa. But I'm never "forced" to drink sports drink when I really want water.
Caffeine is known to cause stomach upset. I normally drink coffee but not before a race because it overstimulates my gut. If it's late in the day on a long race and my tummy feels go, I might take some in the form of Cliff Blocks (since 1 block of Orange = 1/3 a cup of coffee so it's more easily regulated).
When Your Stomach Acts Up:
Take care of it earlier, rather than later. Mild symptoms will become worse and are much harder to reverse when the GI distress has progressed from yellow to red.
Pop Some Pills
Practice in training so you know how you respond. However, don't be afraid to down 2-4 Tums or Gas-X. Do it earlier, rather than later. Remember, you will have to wait 15-20 minutes for a benefit (luckily it should take effect sooner since our blood is flowing and our heart rates are up). Other meds that have been heaven-sent for me include Bean-O, Pepcid, and Immodium. Avoid Advil or Ibuprofen--this is really hard on the stomach.
The blood is shunted to your muscles and away from your gut when running, making it more difficult to digest food. If there is stuff in your gut (i.e. GUs, gels, etc.), this makes it difficult to digest. First thing to do when your tummy begins to rumble is slow down. Sometimes it just needs a little time to process the GU you just slammed. Also, when we race, we often go faster then in training. Often, this causes a surprise GI upset. Just be aware if your stomach starts complaining on race day but was quiet in training, it may be because of your adrenaline-spiked speed.
Drink and Eat More
Sounds counterintuitive but GI upset is the first sign of dehydration. I force down some water and liquid calories at the first sign of a rumble and wait 5 minutes. If I feel worse, I try something else. 9 times out of 10, however, my stomach feels better.
Go to the Bathroom
Much better to get it over with and out of your system and go on with your race than to hold it and suffer for hours on end. Often, once relieved, your stomach will settle down.
Overall, I have to say that triathlon and exercise have improved my IBS symptoms on a day-to-day basis. And, my stomach has gotten "tougher" in training and in races because I'm so used to dealing with it. I can recognize the early signs and correct them before it gets out of hand. This may actually be an advantage for me in really hard conditions, like heat, where everyone comes down with GI problems. Other athletes who've never had stomach upset don't know what to do. I, however, knew what to do 30 miles ago. Sometimes, I think it's my body's way of signaling to me that something is amiss (like with my pace or nutrition). Some people get calf cramps; I get GI distress.
Links on Running and GI Distress: