Although intense exercise can trigger the release of those “feel-good” hormones, aka endorphins, if you have a sensitive stomach or a GI condition like IBS or Crohn’s disease, your gut won’t always agree with your training plan. It’s not uncommon to experience exercise-induced digestive issues like nausea, gas, cramping, stomach pain, and even vomiting or diarrhea mid-workout or after an especially long or intense session.
The good news? These symptoms are usually temporary. But that doesn’t mean they won’t put a, well, cramp in your workouts. “While they don't have harmful effects on long-term health, they are uncomfortable and can certainly hamper performance,” says Kelly Jones, MS, RD, CSSD, LDN, a board-certified specialist in sports dietetics.
Why intense exercise might lead to digestive issues
While hard workouts can be great for your overall health, they're not always kind to your GI tract. Since blood flow is directed to the muscles when they're working really hard, there’s less blood supply available to aid in digestion, according to registered dietitian Trista Best, MPH, RD, LD. As a result, your pre-workout meal or snack gets stuck in your belly, then ends up jostling around during aggressive movements.
How “intense” does exercise have to be to cause a problem? “You might be performing high repetitions with max effort, and with an elevated heart rate that’s around 70 to 85 percent of your maximum rate,” says Best. And you’re likely moving speedily—running or cycling to the point where you’re out of breath and dripping in sweat. “This might apply to people participating in distance cycling or HIIT workouts, or who are conditioning for sports or heavy lifting competitions, for example,” says Jones.
Fortunately, even if you’re prone to digestive distress, you can ease the issues by being vigilant about what you’re eating, when you’re eating it, and in what quantities.
Best tips for fueling for intense exercise
1. Time and choose your fuel wisely
In general, eating too close to working out increases the risk of GI pain and gas. “This is essentially because your body has to multitask between digesting your food and fueling your muscles, so both become inefficient and good gut bacteria starts to release gas as a side effect,” says Best.
Give yourself a few hours after a big meal to digest before pushing your body too hard. Then, “snack 30 to 60 minutes before activity to ensure your blood sugar doesn't rise and fall before you start moving,” says Jones. If you’ll be training for over an hour, consider a snack 5 to 15 minutes before you start, or nibble mid-workout to replenish electrolyte stores and avoid cramping up.
Know that protein and fat take longer to digest, so you’ll want to keep both minimal pre-workout, says Best. Instead, Jones recommends focusing mainly on simple carbs, since they’re absorbed into the bloodstream faster and are ready to use as immediate energy. Adding just a small amount of fat and protein, however, will boost satiety, fuel muscles, and offer electrolytes without weighing you down. So what does that all look like? Smart examples include oat bars, hummus on a slice of white toast, a banana with a bit of peanut butter, and trail mix.
2. Avoid sugar alcohols
“Restrictive diets can make food reactions more common,” says Jones. This is especially true with foods containing sugar alcohols like xylitol. These sugar substitutes have been shown to trigger GI reactions in people with sensitive stomachs and IBS. They’re particularly common in low-carb, low-calorie, and sugar-free packaged foods like protein bars and diet sodas or teas. Check labels for sweeteners that don’t lead to GI pain: Good options include monk fruit and stevia, which don’t elevate blood sugar and shouldn’t cause any trouble for your gut.
3. Fuel with sports gels or drinks
“Sports nutrition products may be smarter to use than real foods for those with GI distress, since sports drinks and gels are mixed carbohydrate sources, so the intestines can better absorb them,” says Jones.
Consider swapping food for a sports gel, beverage, or even honey if you want something more natural. Jones suggests SuperStarch, a mixed carbohydrate source that’s great for long workouts and is less likely to cause GI discomfort.
4. Skip dairy if you’re sensitive to it
Though not everyone finds dairy to be a trigger, many do, so avoid it pre-workout if you know you fall in that camp. And take note of sources that are less obvious, like protein shakes. “These protein shakes are typically dairy-based and can cause GI upset in those with sensitivities when consumed too close to an intense workout,” says Best. Even if the shake is vegan, you don’t want protein in excess before training, either.
5. Sprinkle on a little salt
Salt is actually helpful prior to intense exercise, since sodium is an electrolyte that your body loses through sweat—and in higher amounts with harder workouts. Having greater stores to start with can help stave off gut distress. “Low fluid intake results in GI problems and cramping, and sodium helps maintain fluid balance and improve carbohydrate absorption,” says Jones.
Toss some salt on your pre-workout oatmeal or grab a handful of saltine crackers. “Saltines are bland and easy to digest for quick fuel in the form of glycogen for a workout,” says Best.
6. Save the greens for your recovery meal
“While vegetables like broccoli, Brussels sprouts, and cauliflower are nutrient dense and incredibly healthy, they can be difficult to digest and result in nausea and gas during an intense workout,” says Best. The same goes with legumes like black beans, chickpeas, and lentils.
Eat your high-fiber foods after exercising instead, and pair them with protein for muscle repair. “Post-workout is a good time to take in the protein you've been avoiding prior,” says Best. “A protein shake, nut butter, or veggies with hummus will quickly replenish your body's amino acids to build muscle and boost glycogen stores.”
7. Introduce new foods slowly
Don’t be too aggressive when adding pre- or mid-workout fuel into your routine. “People are deep into training and then decide to add in a gel, sports drink, or even bananas during exercise, but have horrible GI distress, so think they shouldn't be fueling,” says Jones.
You definitely should be fueling, but sometimes it takes some getting used to. Start small by fueling for shorter workouts, and make sure you're balancing your food intake with ample fluids and enough electrolytes and sodium. Consider it to be “training your gut,” says Jones.
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