Plus, the steps you can take to prevent those unpleasant side effects.
A few miles into your first long-distance jog, you might follow through on the fueling instructions any experienced runner provides newbies: Nosh on an energy gel or slurp down a gel to keep yourself from hitting a wall. But in some cases, you may quickly develop gas, bloating, abdominal pain, nausea, or a desperate need to poop. If you’re lucky, you may even experience a blend of all those unpleasant side effects.
There are a couple of reasons you might have to hit the park’s porta potty after scarfing down one of the pre-made energy snacks designed for endurance athletes, says Supriya Rao, M.D., a quadruple board-certified physician in internal medicine, gastroenterology, obesity medicine, and lifestyle medicine, and a managing partner at Integrated Gastroenterology Consultants.
The first and simplest explanation: The physical act of running, whether you eat an energy chew or not, increases the motility of your gastrointestinal tract, or how fast and easily food moves through your digestive system, says Dr. Rao. In turn, you may feel the need to have a bowel movement. Plus, jogging causes oxygen-rich blood to be diverted away from your GI tract and pushed toward your extremities, particularly the muscles powering your movement, she adds. This reduced blood flow can lead to nausea, vomiting, abdominal pain, and diarrhea, research suggests.
The high sugar content of energy goos and gels can also send you straight to the bathroom, says Dr. Rao. A single Honey Stinger energy gel packet boasts 24 grams of sugar from honey, for example, while a serving of CLIF BLOCKS contains 24 grams of carbs, 12 grams of which come from added sugar. The problem: Your body can’t process a large amount of sugar in a short amount of time. As the food sits and slowly digests in your GI tract, the bacteria in your gut will begin to interact with and ferment it — leading to gas and that desire to find a restroom ASAP, explains Dr. Rao.
Compounding the problem is caffeine, which is often included in energy snacks and generally increases gut motility, says Dr. Rao. “While caffeine is designed to give you a boost of energy, I don't really recommend it for working out,” she explains. “It does increase your heart rate, it's very dehydrating, and, if you're in the middle of a race, it can make you want to run to the bathroom.”
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So why do some runners get away scot-free after noshing on a cherry-flavored chew mid-workout? The type of sugar used in the product matters. Your gut contains specific proteins called carbohydrate transporters. They move the carb-derived energy from your gut to your bloodstream, which then delivers it to your working muscles, Dr. Rao explains. “But if you are giving [your gut] such a load that your transport proteins can't transport [the carbs] fast enough, that's when they hang out in the gut and cause that fermentation and all of those symptoms,” she says. Long-lasting carbohydrates, including maltodextrin, are less likely to undergo that gas-inducing fermentation process than fast-acting carbohydrates, such as glucose and fructose, says Dr. Rao.
You may also be more likely to experience stomach upset from your energy chew if you generally have a “sensitive stomach,” says Dr. Rao. “There are millions and millions of nerve endings in your gut,” she explains. “...For all the patients who come in with IBS or other functional GI disorders — where nothing is organically wrong but the nerve endings are causing a lot of pain and whatnot — we tend to see these kinds of symptoms more in those patients.”
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Regardless of the cause, there are steps you can take to minimize and potentially prevent these uncomfortable side effects. Consider swapping your sugar-rich energy product with a snack that offers a mix of long- and short-acting carbohydrates, suggests Dr. Rao. You might make a homemade energy ball consisting of oats, dried fruit, and nuts, for example. “It won't spike your blood sugar so high,” she adds. “It's going to be more of a consistent blood sugar profile to allow you to use that energy in a way that's not going to cause GI upset and [give you] energy over a longer period of time.”
If you love the convenience of pre-packaged products, spend some time testing different varieties to see what works best for you, advises Dr. Rao; just make sure these experiments happen during training, not on race day.
Also important: staying on top of hydration. When products rich in simple carbohydrates hit your GI tract, your body pulls water from your blood vessels to help you digest the food. According to Dr. Rao, without amping up your water intake, you increase your risk of dehydration, which may already be high if you’re exercising in a hot, humid environment. As you exercise, sip on a low-sugar, electrolyte-rich beverage to counteract any dehydrating effects of your carbohydrate-heavy snack, she says.
Of course, the fundamental rules of healthful living still apply; getting enough sleep, prioritizing recovery, and eating a well-balanced, nutritious diet can all help reduce your odds of gastric distress while running. “It's hard to predict [who experiences side effects]. Some people who you wouldn't think would do fine with [energy snacks] do fine, and some don't,” says Dr. Rao. “It's just really dependent on what their normal lifestyle is…I feel like people want an easy answer, but it really comes back down to those basics."