Avoiding Stomach Upset as a Runner

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Avoiding Stomach Upset as a Runner

Heidi Strickler | Fitness, Food & Nutrition, | June 14, 2017

If I were to tally up the topics of all the nutrition questions I have gotten from runners over the years, the issue of stomach upset would take the cake by a landslide.

Why is it that just about every runner deals with stomach issues, be it diarrhea, bloating, gas, heartburn, sloshy stomach, cramps, and/or indigestion?  

Due to the up and down motion of running, it is more likely to cause digestive issues than other endurance events. Imagine eating Thanksgiving dinner then jumping on the trampoline or a pogo stick for several hours – not a pleasant thought, but one many of you can likely relate to. The longer you exercise, and the greater the intensity, the less blood is available to digest your food, which is why most stomach issues don’t happen in the first mile.

Conveniently, most runners are making the same mistakes on the run, which makes for an easy fix:

Mistake #1: Too much simple sugar

Sports drinks, blocks and gels are the primary fuels used in running events. What do all of these have in common? Simple sugars. Excess simple sugar draws water into our intestine, which leads to that notorious gurgle, cramp, and diarrhea. To meet our caloric needs during exercise, simple sugars have to be consumed beyond what our body can absorb. Ever feel like your body is rejecting that 3rd, 4th, or 10th gel? That’s because it literally is.

The Fix: Fuel with more complex carbohydrates (such as maltodextrin, or fresh/dried fruit), which can meet your caloric needs in a smaller volume. Maltodextrin also increases our blood sugar quickly, but does not cause a steep spike in insulin, which can lead to a blood sugar crash. The benefit is three-fold: We can consume less to meet our energy demands, we don’t end up with a bonk, and we avoid a sloshy stomach. Anything over three hours and you should include some source of protein (ideally soy protein, in a ratio of 8:1 carbs:protein).

Mistake #2: Improper hydration

Most runners relying on water alone for hydration, or use a sports drink made up of glucose (dextrose), fructose, and sucrose.   Both can be problematic, for the same reason: concentration. Water’s concentration (or lack of) does not match well with the concentration of our body’s cells, so it can’t be fully absorbed, and electrolytes are pulled from our cells into our intestine. This means that we are not absorbing all of the water we are drinking, which leaves it sitting in the gut, causing a sloshy stomach. We are also losing electrolytes, which we will eventually pee out. This can make us feel dehydrated, so we drink more water, and exacerbate the cycle. The same problem occurs with simple sugar-based drinks: the concentration (if mixed to meet our calorie needs), is too great, so water is pulled into our digestive tract, which results in diarrhea.

The Fix: The recommended fluid intake in moderate climates is 16-28 ounces of fluid/hour. However, due to decreased absorption during running, you should start small and see what you can tolerate. You can always drink more, but you can’t un-drink (well, you can, but it’s not desirable). It is recommended that you use water only to chase a concentrated liquid or solid fuel, such as Hammer Perpetuem, or a gel, block, or food. At other times, use electrolyte tablets (Endurolytes, Nuun, Gu Hydration) or complex carbohydrate-based drinks that use maltodextrin, cassava, etc. (Heed, Race Rx). Oh yeah – and hydrate adequately on a daily basis – aim for 0.5-0.6 ounces of water per pound of body weight.

Mistake #3: Using salt tablets

Or pickle juice, or olives, or salt packets – pick your poison, because that is what it is. When we sweat, we lose salt, and we crave salt. But we neglect other electrolytes in the process. Excess sodium alone puts our bodies in a negative feedback loop – the more sodium we take in, the more our body will get rid of through sweat. In addition, excess sodium without adequate potassium or other electrolytes can result in cramping, swelling of the arms and legs, and increased blood pressure.

The Fix: Aim for a full spectrum of electrolytes, including magnesium, potassium, calcium, manganese, and no more than 100-600mg sodium per hour. Stick to a low-to-moderate sodium diet on a daily basis. The “I sweat a lot so I can eat a lot of salt” thinking is no longer recommended. If you aim for 1,500-2,300mg sodium daily, your body will become more efficient at conserving salt on your runs.

Mistake #4: Trying to eat what your burn

In our “techie” day and age, most runners will utilize a Garmin or similar device to track pace, mileage, calories burned, etc. While useful in many ways, these can also lead people to overconsume calories, thinking they have to replace what they burn while on the run, or that they get to replace what they burned afterwards. Both are a bad choice. When it comes to eating while running, the body cannot efficiently absorb and digest as many calories as it is losing; trying to replace those calories will leave you with a brick in your stomach. Oftentimes Garmins over-estimate caloric burn, and the notion of “I ran so I can eat more” will only lead to fat gain.

The Fix: For most athletes, 120-180 calories/hour on the run is adequate. Larger athletes need more, smaller need less.  You also need more calories (and less fluid) when running in colder temperatures, and fewer calories (and more fluid) when running in extreme heat. While this may seem minimal, the body is incredibly efficient at using its energy stores, and if we train it to preserve fuel, it will. A safe estimate is to take in 1/3 of what is lost, for calories, fluids, and electrolytes.

After runs, consume adequate protein and carbohydrate within 15 minutes to help recovery. Follow this with a meal that is balances in protein, healthy fat, and fiber, to help continue recovery and control appetite. And always refuel with adequate water.


Interested in a nutrition periodization guide with your training? Hoping to optimize your body composition for racing season? Want to avoid cramping?

Call the front desk at 425-776-0803 to schedule an appointment with Registered Dietitian Heidi Strickler, and learn how to eat your way to success!

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