Your Guide to Fiber Intake for Runners
May 3, 2024
It’s a dreaded scenario for many runners: you take a gel during your race, and within minutes your stomach revolts. Nausea, vomiting, urgency, and cramping are all common symptoms of gastrointestinal (GI) upset during marathons and other races. While many factors can be responsible for GI upset, some runners are concerned about their running gel causing their GI issues. The answer is not skimping on fueling – instead, you can try running gels for sensitive stomachs.
Running gels are concentrated formulas containing easily available carbohydrates. Most gels contain 20 grams to 30 grams of carbohydrates.
The formulation of a gel allows you to consume it without chewing. The gels can often be consumed with a few swallows, thus minimally disrupting your running. You can take them at higher intensities, which is why many runners prefer them when racing.
Because of the high carbohydrate content, many running gels require four to six ounces of water to aid in absorption. If you do not consume enough water with your gels, the risk of GI upset increases.
Typically, running gels contain two forms of carbohydrates: glucose and fructose. Glucose and fructose are both monosaccharides – meaning the simplest form of carbohydrate. Both glucose and fructose can be quickly absorbed by the gut, sent via the bloodstream to working muscles, and converted into energy. These two monosaccharides use different gut transporters, which allows you to consume and uptake more total carbohydrates than just one form alone.
Two main issues can cause GI upset with running gels: osmolality and ingredients. Traditional gels are highly concentrated carbohydrate formulas that must be taken with water. If you do not take them with them with water, they pull water from the gut in order to be absorbed. This process alters gastric emptying rates, leading to GI upset. The ingredients can also cause GI upset, particularly if an individual has a condition such as IBS or IBD.
As stated above, many running gels contain fructose. Fructose is a monosaccharide (simple sugar), similar to glucose. However, unlike glucose, fructose needs to be metabolized in the liver into glucose before it enters the bloodstream. The ratio varies; some gels use 2:1 glucose:fructose, while newer products use 1:0.8 glucose:fructose.
However, fructose can be a gastrointestinal irritant for sensitive individuals. Fructose falls under the FODMAP category – foods that are poorly absorbed in the small intestine and can ferment in the large intestine. For athletes with IBS or IBD, FODMAPs can be a trigger for GI upset. It’s a dose that makes the poison type issue: small amounts may not be bothersome, but large amounts over several hours can irritate some runners.
Some research indicates that minimizing FODMAP consumption around running can reduce gastrointestinal symptoms. A 2019 randomized controlled trial in the Journal of the International Society of Sport Nutrition found that reducing FODMAP in the diets of healthy, recreational and trained athletes helped reduce the occurrence of gastrointestinal symptoms. A 2023 systematic review in Nutrients reached a similar conclusion, that low FODMAP diet can be part of a strategy for how to prevent runner’s stomach.
If your issue seems to be related to fructose, pay close attention to the labels of running gels. Some great products (such as Maurten) contain nearly equal ratios of glucose and fructose, which could irritate some people. If this is the case for you, opt for low-fructose gels. Huma is one of the most popular lower fructose gels, especially if you get the berry flavors and forgo any apple flavors.
If hydration and not fructose is the issue, you may want to consider some of the newer gel products on the market. Certain brands of running gels can be taken without water. These brands Maurten, Precision, Science in Sport (SIS), and Neversecond – all hydrogels or isotonic gels.
A 2022 study in Medicine & Science in Sports & Exercise found that GI symptoms were less severe when a hydrogel was used compared to a nonhydrogel. However, the placebo had the same effect on GI symptoms as the hydrogel. This is also not a definitive conclusion, as other studies reported no significant difference in GI symptoms. Additionally, all studies used relatively small sample sizes.
However, hydrogels and isotonic gels do not give you permission to skip your hydration. Dehydration is one of the most influential factors for gastrointestinal upset when running. These gels simply allow you to take them independent of fluid and may lower the risk of GI upset.
Related: How to Fuel on Long Runs
Importantly, this is a generalized list – there are no guarantees that every one of these gels will work for you. Approach this list as a starting point. Try these gels on training runs to ensure they work for you. Ideally, you want to try them on both long runs and race pace workouts.
Most of these gels can be purchased at your local running store, REI, or speciality online shops such as The Feed. (This is not sponsored.)
Across my sample size of athletes, the brand most reported as one of the best running gels for sensitive stomachs is Huma Chia Energy Gel. Athletes with histories of GI problems report that these gels sit well with them. Huma gels use fruit puree, cane sugar, rice syrup, and chia seeds to provide a gluten-free source of carbohydrates. The texture is thin and easy to consume.
Huma also offers an electrolyte gel for runners., which provides sodium as well as carbohydrates. If you do not like sports drinks or have high sodium needs, you may benefit from the higher electrolyte gel.
Many runners also report that Maurten sits well with them, especially if they are aiming for a high carbohydrate intake during their race. The hydrogel technology encapsulates the carbohydrate, so that it is not released until it can be absorbed in the small intestine. By bypassing the stomach, it theoretically has lower risk of GI upset.
Notably, Maurten does have a higher fructose concentration than some other gels. So while it may work for some, these hydrogels are not universally the best running gels for sensitive stomachs.
Precision Fuel Gel provides 30 grams of carbohydrate per gel, with a 2:1 ratio of glucose-fructose. While it may not sit well for athletes who are very sensitive to FODMAPs, many runners report that the mild, neutral flavor makes this tolerable. The addition of pectin creates a hydrogel type formula, which makes it potentially a good running fuel for sensitive stomachs.
For athletes sensitive to large amounts of fructose, some of the best running gels for sensitive stomachs are whole food gels. If you avoid high-FODMAP fruits (such as apple), these gels often are easier to digest.
Muir energy gels and Spring energy gels are two options. The one downside is that these gels are sometimes lower in carbohydrates, meaning you may need to take more per hour to hit your carbohydrate goals.
Isotonic gels have added water, to create a thinner texture and promote rapid gastric emptying. Isontonic means the concentration of the gel is the same as your gut wall cells, so no osmotic movement is required to absorb the gel – thus quicker gastric emptying. Quicker gastric emptying reduces the risk of gastrointestinal upset during running.
Isotonic gels include Neversecond and Science in Sport (SIS). Another benefit of these gels is that the isotonic formulas allow a higher concentration of carbohydrates (30 g for Neversecond, 40 g for SIS Beta Fuel) – allowing you to theoretically take fewer total gels to hit your intra-run carbohydrate goals.
The recommendations for how to prevent runner’s stomach extend beyond the type of running gels you use. Factors such as caffeine, hydration, your pre-run meal, and gut training all impact how your GI system feels during a run.
Some running gels contain caffeine for a performance boost. However, caffeine may not be an ideal component of running fuel for sensitive stomachs. A very common side effect of caffeine consumption is gastrointestinal distress. If you have GI upset during runs, check the amount of caffeine in your running gels – and consider opting for non-caffeinated running gels. (All gels listed above have non-caffeinated options).
Whether or not your gel requires simultaneous fluid ingestion, you want to be hydrated during your runs. Dehydration significantly delays gastric emptying – by up to 25%. This reduction in gastric emptying can increase the likelihood of GI upset. If you want to prevent runner’s stomach, bring water or a sport drink with you and aim to drink roughly 8-16 oz per hour (based on sweat rate).
Research demonstrates that you can train your gut to tolerate more carbohydrates in training. Your body adapts its gastric emptying rates, gut transporters, and even carbohydrate oxidation rates in response to carb intake during long runs. The more you fuel on long runs, the better your gut will tolerate it. Start with small amounts of fuel and gradually build up over time.
Your pre-run meal is essential. A pre-run meal provides energy for your run, which enhances performance, promotes endocrine system function, and reduces risk of injury due to low energy availability. However, eating too large of a meal too close to the start of your run can cause GI upset.
If you have 90 minutes or less, aim for a small, easily digestible pre-run snack. This should be something high in simple carbs and low in fat, protein, and fiber. If you have more than 90 minutes to digest, you can eat a bit more and include a small amount (<10 g) of fat and protein.
Related: What to Eat Before a Run
GI upset during runs and races can be complex. Many variables can cause nausea, vomiting, urgent bathroom stops, and cramping. While running gels are only one of those many variables, they can be a trigger for some runners. Your strategy for how to prevent runner’s stomach may include trying running gels for sensitive stomachs.
Don’t like the texture of gels? Other options include:
If the issue is not resolved, do not hesitate to contact a sports dietitian to work through your GI issues. They can take a holistic look at your fueling, diet, and other factors.
Want more training tips including sport nutrition guidance? We answer all your running questions – including gels for sensitive stomachs – on the Tread Lightly Podcast!
