Training Your Gut For Endurance

Training Your Gut for Endurance

BY Philip Mosley

Eat more, race faster. Yes, you read that correctly — if you train your gut to consume more calories, you’ll improve your endurance-sport performance. Here’s what you need to know.

What’s held you back from better performance? You may think that your training isn’t efficient enough, or that you should start incorporating more strength workouts into your current program. Those are great places to start looking into, but one often overlooked aspect of training is a bit more internal — that is, your gut.

Many endurance athletes could benefit from consuming more calories on race day, which will help you to maintain energy throughout the event so that you cross the finish line strong. Take the example of the legendary Brownlee brothers — triathletes with two Olympic gold medals, one silver, and one bronze between the two — and their epic fail in the Mexico World Triathlon Series race in 2016. The heat and intensity of the race had drained Jonny of energy, leading to dizziness and rubbery legs. Alistair prevented his younger brother from hitting the blue carpet, scooping him up and dragging him over the finish line. Victory was very well lost because Johnny hadn’t properly fueled himself.

The thing is, your gut needs to be trained to handle more calories, or else you’ll face a slew of gastrointestinal issues that could very quickly ruin your race. Here’s what you need to know.

How Your Body Processes Energy During Exercise

During endurance, ‘steady state’, or low- to medium-intensity exercise, the bulk of your energy is derived from fats that are broken down via the aerobic energy system. One pound of fat stores roughly 3,500 calories, so even a professional cyclist with 8% body fat has a plentiful supply to tap into. 

Things change when you crank up the intensity. Your muscles’ desire for energy can’t wait for oxygen to slowly break down fats or more complex stored carbohydrates. It needs an instant hit, which comes from breaking down carbohydrates via anaerobic glycolysis. The problem is, your body can only store around 300-500 g of carbs in the form of glycogen. Burning one gram of glycogen releases just four calories, meaning your body’s carbohydrate storage capacity is between 1,200 and 2,000 calories. During long events, this can easily leave you feeling low in energy. 

Training Your Gut for Better Endurance

Because of the way our bodies process energy, endurance athletes have to fuel throughout a race, be it from drinks, gels, blocks, and/or bars. And this is where training your gut can prove beneficial. “In general, an athlete can burn around 60 grams of glucose every hour of exercise,” explains Patrick Wilson, author of the acclaimed The Athlete’s Gut: The Inside Science of Digestion, Nutrition and Stomach Distress. “That said, some athletes run into problems at around 40-50 g/hr of glucose, while some athletes can handle 90 g/hr or more via a glucose-fructose mix — especially if they spend time training their gut.”

Wilson provides us with two valuable insights here: glucose-fructose mix and training your gut. The former is a relatively well-known concept that advocates for adding fructose to glucose, which theoretically raises your carbohydrate ceiling from 60 g/hr to 90 g/hr because fructose is transported across the intestine via a different channel than glucose, so there’s no internal sugar traffic-jam going on.

This concept is theoretical because it’s rare that an athlete who is used to consuming 60 g of glucose an hour can effortlessly jump to 90 g (with the addition of fructose) without some form of stomach issue. That’s where training your gut comes in, which you can start to do by eating during your next workout. “Studies have shown that regularly eating 60-90 g/hr of carbohydrate during training can increase tolerance to aggressive feedings,” says Wilson. “Some of the adaptations probably relate to stomach emptying, while others involve upregulating the expression transporters that shuttle sugar molecules into intestinal cells.”

How Long Does Gut Training Take?

“The big question is how often an athlete needs to do this ‘gut training’ to reap the benefits,” Wilson continues. “Costa et al. had runners do 10 days of gut training over two weeks in one experiment, but I’m not sure how practical that approach is for most athletes. I’d suggest gradually increasing carbohydrate intake once or twice a week. For example, start at 30 g/hr during a longer training session and add 10 g/hr every week until you reach your target.”

Wilson suggests that the adaptations he’s talked about happen pretty quickly – “within a few days or a week” – so it’s not necessary that endurance athletes need to be training their gut 52 weeks a year. That’s a lot of sugar, which your molars and dentist won’t thank you for! “Instead, it’s a better idea to periodize gut training like any other training,” he adds. “I would focus on it more as you get closer to certain competitions where you expect to ingest a high rate of carbohydrate.”

This periodization might see you bypass the 90 g/hr point and carry on consuming. A study in the American College of Sports Medicine showed that a handful of athletes can handle upwards of 120 g/hr. But, says Wilson, this really isn’t necessary for most athletes.

There are also caveats about transferring lab-based results into the real world. One of the authors of the aforementioned study, Peter Res, showed how former IRONMAN record holder Marino Vanhoenacker could consume 120 g/hr in the laboratory but took those results to IRONMAN Hawaii and suffered awful gastric issues. “It was down to the heat,” Res explained. Needless to say, Vanhoenacker subsequently dropped below 100 g/hr and avoided stomach complaints.

Learning From a Different Type of Competitor

Still, maybe Vanhoenacker could have coped with 120 g/hr, whatever the heat, if he had learned from competitive eaters. It’s known that this hungry band of men and women train their stomachs to hold large volumes of food through a meticulous training program that can see them consume ridiculous amounts of grub. Take the current all-time record of eating 69 hot dogs — bun included — in just 10 minutes!

Sports nutrition scientist Asker Jeukendrup says that to achieve this hungry hallmark, competitors use a range of methods including chewing large pieces of gum for long periods of time, drinking large volumes of fluids, and eating huge amounts of food.

Jeukendrup applies this knowledge to an exercise environment and says that training with relatively large volumes of fluid, and training immediately after a meal, are methods to reduce bloating during exercise and, ultimately, to increase your capacity to absorb carbohydrates.

So there you have it. This is your free pass to eat and drink more in the name of performance. What right-minded endurance athlete wouldn’t raise a glass or two to that?


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About Philip Mosley

Phil Mosley is Head Coach and founder of MyProCoach. He has over 20 years’ coaching experience and his training plans are followed by over 10,000 endurance athletes each year. Follow his regular training advice via Instagram (@myprocoach_).

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