Amy Stephens
MS, RDN, CSSD, CEDS
Licensed dietitian
specializing in sports nutrition
and eating disorders
Gut Training for Athletes
- Amy Stephens, Sports Dietitian
- Kate Cochran, Nutrition Intern and NYU XC Athlete
Many endurance athletes avoid fueling during long runs or rides because it feels uncomfortable or causes gastrointestinal (GI) issues. But often, that discomfort isn’t due to fueling itself—it’s because the gut hasn’t been properly trained. Being able to ingest carbohydrates during an endurance event will improve performance. It will enable you to exercise at a higher intensity for longer without running out of energy.
This is where gut training can be a great thing to start experimenting with.
Gut training is the process of gradually teaching your digestive system to handle fuel—specifically carbohydrates—during exercise. Just like your muscles adapt to training, your gut can adapt, too. With consistent, intentional practice, your gut can start adapting in two weeks, becoming more effective at:
- Emptying food and fluids faster
- Absorbing carbs more effectively
- Reducing symptoms like bloating, cramping, or nausea during long workouts and races
And the science backs this up:
- The gut can adapt over time. Studies show that with repeated carbohydrate intake during exercise, the stomach and intestines improve their ability to digest and absorb fuel. Athletes who consistently practice fueling are able to oxidize (use) more carbs during training and racing than those who don’t.
- Carbohydrate oxidation increases. Gut training enhances your body’s ability to use carbs for energy—especially when using a glucose + fructose mix, which taps into two different absorption pathways. This is important because higher oxidation rates increase the amount of carbohydrates that can be consumed and used for energy without causing GI issues. Ingesting more carbohydrates preserves muscle glycogen for longer. Many endurance athletes can eventually tolerate up to 90g of carbs per hour, which is key for performance in longer events.
- Fewer GI issues on competition day. Athletes who practice fueling in training are far less likely to experience cramping, bloating, or nausea during competition. In contrast, those who wait until race day to introduce fuel are more prone to GI distress.
With consistent gut training, you’ll be able to take in more fuel with less discomfort—helping you avoid energy crashes, improve performance, and feel stronger all the way to the finish.
Practice Pre-Workout Fueling
In addition to fueling during runs, I’ve also found that consistently eating before and after workouts has made a big difference in how I feel and perform. Taking in carbohydrates before a run gives me the energy I need to get through the run feeling strong, and fueling afterward helps me recover faster and stay consistent with my training. With consistent gut training—and by giving your body the fuel it needs before, during, and after your workouts—you’ll be able to train harder, recover faster, and perform at your best.
Here are some quick things that I like to eat before a run:
- Banana with peanut butter, sea salt, and cacao nibs on top
- Sourdough toast with peanut butter, bananas, cinnamon, & honey drizzled on top
- Frozen waffles with nutella and strawberries on top
- Oatmeal with frozen fruit, nut butter, and chocolate chips
- *If you have a sensitive stomach, studies have shown that white toast, applesauce, banana, or boiled rice are great options.
Start Fueling During Training and Gradually Increase Carb Intake
Fueling during workouts longer than 90 minutes plays a key role in effective gut training. These longer sessions are ideal for helping your digestive system adapt. Fuel at regular intervals with fluids and electrolytes.
- For workouts up to 2½ hours, aim for 30–60 grams of carbohydrates per hour.
- For sessions over 2½ hours, increase intake to around 80 grams per hour, using a mix of carbohydrate sources (glucose + fructose) to improve tolerance and absorption.
- Hydrate with 10-20 oz fluids about two hours before + electrolytes.
Here are some great options that use a variety of carb sources:
- Gels typically provide 22–25 grams of carbohydrates each, though some newer options offer 30–40 grams per gel for higher fueling needs.
- Sports drinks such as Skratch or Gatorade provide hydration and carbohydrates.
- Natural gels made from maple syrup or honey may be better tolerated such as Honey Stinger, Huma or Untapped.
- Food options can include dates or other types of dried fruit.
- *Longer endurance events such as ultra marathons or long cycling events will benefit from solid foods such as bananas, pretzels, Fig Newtons or other easily digestible carbohydrates.
- Practice your fueling plan in race-like conditions.
Here’s what I typically eat directly after a run (second breakfast)
- 2-3 scrambled eggs with salt, pepper, and parmesan cheese, with a few slices of sourdough toast, avocado, and arugula
- Greek yogurt smoothie (my favorite combo right now is ⅔ a cup of Greek yogurt, almond coconut milk blend, 1 and ½ bananas, a handful of fresh or frozen mango chunks, a handful of strawberries, a handful of fresh or frozen slices of peach, and a scoop of vanilla protein powder. With this I would also probably have a bagel or toast on the side.
- Kodiak protein pancakes w/ chocolate chips and bananas.
- *If I’m ever on the go and can’t eat immediately after running, I like to bring a core power protein drink or chocolate milk + a banana with me. I usually do this when we travel for long runs and are an hour away from home after finishing.
Refuel post-workout with a mix of carbohydrates and protein to support recovery and help your gut adapt to fueling.
Being consistent with carbohydrate gut training can enhance both performance and overall health during a training cycle. Longer workouts provide a valuable opportunity to experiment with different foods and sports products to find what works best for your body.
Reference
Cox GR, Clark SA, Cox AJ, Halson SL, Hargreaves M, Hawley JA, Jeacocke N, Snow RJ, Yeo WK, Burke LM. Daily training with high carbohydrate availability increases exogenous carbohydrate oxidation during endurance cycling. J Appl Physiol (1985). 2010 Jul;109(1):126-34. doi: 10.1152/japplphysiol.00950.2009. Epub 2010 May 13. PMID: 20466803.
Jeukendrup AE. Training the Gut for Athletes. Sports Med. 2017 Mar;47(Suppl 1):101-110. doi: 10.1007/s40279-017-0690-6. PMID: 28332114; PMCID: PMC5371619.
Jeukendrup A. A step towards personalized sports nutrition: carbohydrate intake during exercise. Sports Med. 2014 May;44 Suppl 1(Suppl 1):S25-33. doi: 10.1007/s40279-014-0148-z. PMID: 24791914; PMCID: PMC4008807.
Jeukendrup A. Training the Gut for Athletes. 2018. Gatorade Sport Science Institute, SSE#178. https://www.gssiweb.org/sports-science-exchange/article/training-the-gut-for-athletes