Training Your Gut for Athletic Performance

Tanya Jones Digestive Health, Endurance Sport, Food for Runners, Gut Health, Nutrient Timing, Nutrition Tips, Performance, Running Performance, Training 3 Comments

I feel like we have all had an experience or two where you’re out there having a great ride or run and suddenly, you’re out of energy, or feeling crampy and nauseous or in a worst-case scenario looking desperately for somewhere to go the bathroom wishing you had a roll of toilet paper in your pocket.

Fear of these scenarios happening can lead us to limiting how much we eat pre-workout as well as not taking in enough nutrition during our training sessions or race. This is so unfortunate because we know we need to nourish our bodies for the workout that we are doing but even more importantly to support our recovery so we can make the adaptations we are working so hard for as well as set ourselves up well for our next workout.

What Leads to GI Distress?

The gastrointestinal (GI) system is not adapted to functioning well during exercise. You may have heard of the sympathetic and parasympathetic nervous systems, also known as “fight or flight” and “rest & digest”. When you are exercising, your body is predominantly in fight or flight mode and blood flow is reduced to the GI tract as it is diverted to your muscles. This is why gut problems are very common with athletes, especially during endurance events that require you to consume food and fluids during the event. 

Some of the reasons we struggle with gastrointestinal (GI) distress are:

  • Physiological. Blood flow to the GI tract is reduced during exercise.
  • Mechanical.  Either impact-related or related to posture. For example, the jostling of organs while running or compression of abdomen while cycling, especially when in aero position. Symptoms are more common in runners than in cyclists.
  • Nutritional. The gut is sensitive to water and nutrient intake during exercise. Fiber, fat, protein, and fructose have all been associated with a greater risk to develop GI symptoms as well as too much concentrated carbohydrates at one time.
  • Dehydration. Either as a result from inadequate fluid intake to offset sweating, or environmental conditions.

If you struggle with stomach or lower GI distress, you’re not alone. In my time working with athletes, this is a very common discussion we have. The initial options are to fuel less and have a chance of running out of energy and become dehydrated or fuel more and have a chance of getting an upset stomach. Or we take the optimal approach which is somewhere in the middle where you balance intake with stomach comfort and “train” your gut to tolerate the required amount of energy that you need to take in during the types of activities you want to participate and thrive at. The gut is an extremely adaptable organ and can be “trained” in a similar way to the way we train our muscles. While we are great at following our training plan to build our muscles for our chosen endurance sport, nutrition seems to be something that we just wing it and hope for the best. I suggest that you match the time and effort you invest in training your body with training your gut to get the most out of your training and reach your athletic potential.

Where to Start?

Before we look at training your gut during exercise, here are a few tips that can help you support your gut before you even start.

Limit fibre-rich foods
This can be for the days before an event or important training session. You do want to ensure you have adequate fibre in the majority of your diet to help maintain a healthy gut, but fibre can be a problem during an event. Fibre is indigestible, it can result in bloating, gas, and constipation. To reduce this risk on competition day, you can try processed white foods, such as white pasta, white rice, and white bread instead of wholegrain bread, fibre-rich cereals, oats and brown rice (This is the only time I will ever suggest this). Also, most vegetables and fruit are rich in fibres, but there are a few exceptions: zucchini, tomatoes, olives, grapes, and grapefruit all contain less than one gram of fibre per portion and can therefore be eaten as part of a low-fibre diet.

Avoid dairy products
Dairy contains lactose and even mild lactose-intolerance can cause digestive distress while exercising. Lactose may not impact you when you’re not exercising so many athletes may be lactose intolerant without knowing it. I suggest trying a milk alternative to determine one that you like and incorporate that into your pre-event and training strategy.

Avoid foods that are rich in fructose

This actually applies to your everyday diet as well. Fructose is not just found in fruit but also in most processed foods such as soft drinks, sweetened fruit drinks, canned fruits, boxed desserts, flavoured yogurts, baked goods, breakfast cereals and condiments, like ketchup, and jams, in the form of glucose-fructose syrup. It should be noted that naturally occurring fructose in fruits is not the problem here. Fruits are beneficial to health, being an excellent source of fiber, vitamins, and antioxidants. Sports drinks, gels and chews that contain a combination of fructose, glucose and/or maltodextrins are reasonably well-digested as a rule and can even improve tolerance.

Avoid highly concentrated drinks during exercise
Consuming beverages that are very carbohydrate rich (hypertonic) can lead to digestive distress. These highly concentrated drinks usually contain more than 12 g of carbohydrates per 100 ml liquid and slow down gastric emptying. This can result in back up in your digestive system which has two impacts. First, you are limiting access to the energy you need to keep exercising and second, if you keep adding fluid and more fuel to your system, the back up in your GI tract with need to be evacuated by either vomiting or diarrhea. Neither of these options are desirable or pleasant, especially during a race in front of a crowd.  Determining what works well for you will take practice with the timing and concentration of your fuel choices.

Avoid taking NSAIDs
Aspirin and NSAIDS, such as ibuprofen, can both lead to irritation of the GI tract. They both irritate the stomach lining and can lead to long term complications if taken over a long period of time. Your GI tract is already not functioning optimally while exercising and we need to absorb the nutrition we take in, so reducing any irritants that you can is beneficial. If you do need to take either aspirin or an NSAID, take with food to limit this risk but really the use of NSAIDs in the run up to a competition should therefore be avoided.

Start hydrated
As you exercise, your core body temperature rises. In response, your body sweats to dissipate excess heat so it doesn’t overheat. Dehydration can worsen gastrointestinal symptoms, so you want to stay ahead of this by starting your workouts well hydrated. Adequate hydration is also essential for thermoregulation, helping to prevent cramps, heat exhaustion and heat stroke. As well as helping with transport of nutrients throughout your body, maintaining appropriate blood pressure, lubrication of joints, and help eliminate waste and metabolites. So, ensure you are well-hydrated and strive for urine that in lemonade in color.

Practice, Practice, Practice!
Before an important event make sure you have tested out the meals you plan to eat the day before, morning of and all the nutrition items you plan to ingest during your activity. This is important to do in a variety of conditions that will simulate what you will face on your event day. Use all your training sessions as an opportunity to prepare your yourself physically, mentally, and nutritionally. That way you can discover what does and doesn’t work for you and reduce the risk of gastrointestinal problems disrupting your event.

Training Your Gut for Fuel and Hydration

Dial in your fueling strategy

As endurance athletes, we need to come up with a strategy to fuel our bodies while we participate in our activities. Often, we do this with a combination of drinks, gels, blocks, and/or bars. This is where training your gut can prove beneficial to find what works and to expand your ability to process the carbohydrates you need to keep moving forward. On average, we are aiming to take in 60 to 90 grams of carbohydrates per hour for those hard or long (over 90 min) training sessions. But as you know, this can be an issue for some but with practice you can train your gut to tolerate the amount of carbohydrates you need to be energized and thrive through your training and events. Some athletes run into problems at around 40-50 grams per hour of glucose, while some athletes can handle closer to 90 grams of carbs per hour with a mixture of glucose and fructose mix.

Consuming a mixture of fructose and glucose can increase your ability to absorb carbohydrates because fructose is transported across the intestine via a different channel than glucose, so there’s no internal sugar traffic-jam going on. This method does take some training, so your body gets used to using both channels for absorption. Adding too much fructose right away can cause digestive distress as mentioned above but adding small amounts and slowly increasing over time will give your body time to adjust and reduce the potential for GI distress.

Once your gut has become accustomed to the food that you will consume during a competition you will have less chance of gastrointestinal problems. If you always avoid carbohydrates in your daily life, your intestines will be less able to digest carbohydrates efficiently when exercising.  As a result, come competition day, you may not be able to make optimum use of all the carbohydrates you have ingested, which could lead to gastrointestinal problems. You therefore shouldn’t limit your daily intake of carbohydrates, instead you should train your intestines and eat carbohydrates regularly.

Ideally you want to time your intake so that you will ingest small doses of carbs, evenly spaced out throughout the entire workout. I suggesting you start fueling within the first 15-20 min of starting your workout and keep a steady flow every 15-20 min after that. This will be an individual process, but these smaller doses will allow you to process what you’ve taken in before adding more to your digestive system. While you are exercising under intensity or for a long time, you have limited blood flow to your digestive system to allow for absorption and distribution of the nutrition that you take in. If you take in too much at one time you could get a back up and potentially digestive distress, and no one wants that. Try different options and see what works for you and the best timing system based on the activity you’re doing.

Address your during activity hydration

When you think about your fueling strategy, you want to think of hydration as a separate component to fueling. What you are taking in for energy, as we talked about above, and what you will take in for hydration. We have a tendency to think that if we are using liquid fuel options, that counts as hydration, and I suggest that you keep it separate. If you don’t have enough water in your bloodstream, you will have a harder time to temperature regulate, manage blood pressure and very importantly carry the nutrients and electrolytes around your body to where they are needed. An even larger concern is, if the concertation of fuel that you take in, has a higher concentration than your bloodstream, you will not be able to absorb it, leading to lack of energy, cramps and eventual digestive distress. So, you want to make sure that you are hydrating as well as fueling.

A guideline to start with is 1/2 – 1 cup fluid every 20 minutes. In hot conditions, it could go as high as 2 cups every 20 minutes. Aim to drink fluids on a consistent schedule (set a watch timer), do not take an on-the-fly approach.

The amount of electrolytes that you need is also different for each individual. Factors such as sweat concentration, sweat rate, temperature, humidity, individual body chemistry and body composition contribute to your unique electrolyte requirements. How much sodium you should consume during exercise will vary from athlete to athlete. So, experiment in training to dial in what works best for you. As a starting point, try consuming 300-800 mg of sodium per hour. I also recommend that you look into getting a sweat composition test and track your sweat rate over multiple types of workouts to really dial in your plan. I’ve used Precision Hydration (not affiliated to them) and found it to be a game changer, especially in the heat.

It is important to put in just as much effort into your nutrition as you do your workouts. Supporting your body this way will allow you to train harder, recover faster and achieve the athletic potential you are working so hard for.

Happy eating!

Tanya R.H.N.

Sports Holistic Nutritionist

Strength and Conditioning Coach

Multisport Coach

Comments 3

  1. You have anthropomorphized a bodily system. You have asserted without evidence that the digestive system can be trained, like a toddler or a puppy – that it somehow learns or adapts to higher carb loads? Do you have evidence of this? Better to say that you can train your brain, via experimentation and learning, to choose products and fueling patterns that will provide enough calories without digestive upset.

    1. Hey Vince… What an odd comment. What was your intention behind posting? First, may I humbly point out that you have used a very large word out of context. Bodily systems deserve to be “anthropomorphized” as they are 1. obviously part of the human entity; and 2. they operate with a human intelligence of their own that our brains cannot direct (the wisdom of our body extents beyond our brain). Secondly, of course you can train the digestive system – this is nothing new and there is plenty of evidence pointing to such that is easily found. Not least of which has been written about here: https://www.outsideonline.com/health/nutrition/new-science-training-your-gut/. You might note that it’s common to make an assertion without propping it up with evidence when the assertion is now at least half a decade old and no longer controversial or new info. Cheers.

      1. Thank you for the link – I did read it, and the two articles linked within it. I grant that it appears the digestive system may change its reaction to carbs if given a high level of carbs. However, this research is thin, and its usefulness to the average runner is very questionable. The Monash University paper (I could only read the abstract due to paywall) was based on 18 trained runners who could run two hours followed by an hour time trial. So, a pretty select group of runners to begin with. Half were controls, so the effect of carb calories on performance is measured in only 9 people. That doesn’t seem too persuasive to me. What’s more, while their GI distress was reduced, it remained significant.

        The other linked article was a literature review from 2017. It admitted that few studies had investigated “training of the gut,” but gosh he was all for it. (BTW, the article was sponsored by Gatorade.)

        These articles raise more questions than they answer. How long do adaptations take? How quickly do they disappear? If a runner gobbles the gels in the last long run two weeks before a marathon, will the effect be gone after the taper? Must gels or sports drinks be taken daily to produce any adaptation, or is once a week on the long run enough? How does the athlete’s regular diet affect tolerability of high carb gels and sports drinks? After half a decade, as you say, I see little in the way of practical and proven advice and protocols for tolerating higher amounts of race-day nutrition. But boy, I see a lot of people haunting the late-miles Port a Potties.

        Many runners, including me in the past, could benefit from higher calorie intake during endurance exercise. But I see little well-founded research or runner wisdom that suggests that people can solve their endurance nutrition problems via “gut training.” I do think people can improve their comfort and performance by experimenting with different products in different amounts.

        And, the very best advice is to get things moving with coffee two hours before the race or workout! That will erase a lot of sins!

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