As the exercise demand increases, the onslaught on the stomach follows suit. Something that I am often questioned about, particularly in endurance sports, such as triathlon. The reality is a number of factors may play a part in any exercise induced gastrointestinal discomfort. Recently one of the founding fathers in carbohydrate research, Asker Jeukendrup has published a review article on this very topic. At Platform nutrition we want to share our thoughts and uncover some of the practical recommendations they may help reduce or eliminate this race limiting issue.
In sport the gastrointestinal (GI) tract is as important as any of the working muscles. This is particularly true in endurance sports, where external sources of fluid and carbohydrate may have a direct impact upon performance. Without doubt the GI system is extremely adaptable and specific training may improve nutrient delivery during exercise and help protect or limit the commonly reported stresses.
Why do I get gastrointestinal discomfort when training?
There are many potential factors but a common cause and attributing factor is following the ingestion of drinks, gels and solids during exercise, possibly going from empty to a full stomach. This is often accelerated in warm weather or when the exercising demand is high, due to rapid gastric emptying to meet the energy demands required – basically bypassing digestion, or more likely food and drink being held too long in the stomach and causing exercise induced bloating. The good news is the gut is all trainable and not something that you have to endure.
Look after your gut
Yes the gut is trainable, but think logically; if you are exercising really hard and using all the ingested nutrients, coupled with the fact that your body is working overtime to meet the exercising demands, the last thing you want to do is overload an organ that is often susceptible to struggle under stress and quickly, without warning, bite back. The stomach can be a delicate thing and should therefore be treated as such.
Training the gut
Science tells us that endurance performance is impaired when carbohydrate and hydration levels are compromised. To be more precise, in times of carbohydrate depletion and when the body is greater than 2% dehydrated. This then, serves in part as the exercising recommendations and has been well tolerated with minimal GI problems. In fact, many practitioners recommend training at higher intakes to help train the gut, increase the rate of gastric emptying and further minimise an exercise induced complications.
Slow progress with SGLT1
Endurance exercise competitions are based on the speed that you can get to the finish line. In the review by Jeukendrup (2017) he highlights that a limiting factor for the working muscles is receiving the fuel it needs, in this case sugar. The issue is the rate of glucose transportation by the sodium-dependent glucose transporter (SGLT1) being impaired during exercise. Exercisers may wrongly assume therefore that with transport being a limit, just add more carbohydrate, but further studies have shown that the limiting factor resides with the speed of gastric emptying, muscle glucose uptake and liver glycogen storage, rather than the total amount of glucose. Added to the fact that adding more carbohydrate is likely to cause further GI distress. More evidence is required to determine whether transportation improvements can be made to SGLT1 but for now, platform nutrition’s recommendation would be to determine the right amount of tolerated carbs, the not too little and the not too much - All things that you can refine in training.
Top tips to training the gut
Jeukendrup, A. E. (2017). Training the Gut for Athletes. Sports Medicine (Auckland, Nz), 47(Suppl 1), 101.