Practically any endurance athlete has suffered from gastrointestinal problems (e.g., nausea or the so-called "side stitches") during training or worse, in a competition. Gastrointestinal problems are one of the biggest fears of endurance athletes. You can arrive in great physical shape to the competition after months of perfectly planned training, but everything can go wrong when stomach pain begins and you cannot continue, even though fatigue is not the cause.
If this is the case for you, it's important to know that you're not alone. In a very recent study published in the journal Nutrients (Pugh, 2018), researchers went to different marathons and observed that 1 in 4 runners showed gastrointestinal symptoms during the race. In addition, half of the participants suffered discomfort during training. But is there a solution to these problems?
Control carbohydrate intake
Carbohydrates are essential to maintain performance in endurance sports, especially when we talk about long-duration disciplines such as the marathon. In these tests, our body consumes the glycogen we have stored and, if we run out of deposits, the familiar "bonk," or hypoglycemia, can occur. That is why in this type of test we must regularly consume carbohydrates either in the form of bars, gels or isotonic drinks. However, both excessive and insufficient intake can be problematic.
No matter how much carbohydrate we consume, our cells will only be able to transport a certain amount inside to be used. In the case of some of the most consumed carbohydrates such as glucose, sucrose or maltodextrin, this amount is 60 g/hour. In other words, a priori everything we eat above that amount will not be used to obtain energy, and on the contrary the risk of stomach problems will increase. However, this limit of use applies only if we consume carbohydrates that use the same transporter to enter the cell. Thus, if we use two types of carbohydrates that use a different transporter, such as glucose and fructose, we can provide those 60 g/hour of glucose already mentioned along with an "extra" amount of fructose (up to 30 g/hour) that will allow us to obtain more energy without increasing the risk of stomach problems. This fact has been demonstrated by studies in which it was observed that the combined consumption of glucose and fructose (around 108 g/hour) led to a higher performance (8% higher) in a cycling time trial than the consumption of the same amount of carbohydrates but only from glucose (Currel, 2008).
Train the stomach
It is also important to mention that, although carbohydrate tolerance appears to be higher when combining sources that use different transporters, the gut must be trained to tolerate these amounts. Just as we plan training by progressively increasing the loads so that the body adapts, the intake of carbohydrates (and in general, of any food/liquid that is going to be taken in competition) must be practiced beforehand and implemented progressively. As summarized in a review recently published in the prestigious journal Sports Medicine, the intestine must be trained (a process known as "training the gut"). The progressive increase in carbohydrate intake will increase tolerance to carbohydrates as well as their absorption, thus facilitating performance and reducing gastrointestinal symptoms. The author also comments that other strategies such as getting the body used to exercise as soon as you eat (i.e., on a full stomach) or consuming high doses of carbohydrates can facilitate these adaptations.
Figure 1. Methods proposed by Jeukendrup (2017) to produce adaptations in the body that eventually reduce gastrointestinal problems with the consequent improvement of performance.
The microbiota, a weapon against gastrointestinal problems?
It is increasingly being demonstrated that a "healthy" microbiota prevents a multitude of metabolic and digestive pathologies. In addition, recent studies suggest that it could play a critical role in preventing gastrointestinal problems during exercise. A study published a few weeks ago looked at 24 marathon runners who were supplemented for 4 weeks with probiotics (which promote the development of the microbiota) or with a placebo supplement. The researchers noted that the group taking the probiotics had fewer gastrointestinal problems during workouts. In addition, after the 4 weeks of supplementation were over, all participants ran a marathon, and the group that consumed probiotics had fewer gastrointestinal problems than the group that consumed the placebo. Therefore, supplementation with probiotics (or other probiotic foods such as yogurt or kefir) could be an effective strategy against gastrointestinal problems.
In summary, numerous factors can increase the incidence of gastrointestinal problems during exercise, including nutritional variables but also psychological state (e.g. stress) or even environmental variables (e.g. temperature). However, some factors such as controlling carbohydrate consumption, increasing the intake of probiotic foods, and proper planning of nutritional intake on the day of the competition, are in our hands and can be decisive in being able to perform optimally.
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References
Pugh JN, et al. (2018) Prevalence, Severity and Potential Nutritional Causes of Gastrointestinal Symptoms during a Marathon in Recreational Runners. Nutrients. 10(7), pii: E811. doi: 10.3390/nu10070811.
Jeukendrup, AE. (2017) Training the Gut for Athletes. Sports Medicine. 47 (Suppl 1): 101-110.
Currell K, and Jeukendrup AE (2008) Superior endurance performance with ingestion of multiple transportable carbohydrates. Med Sci Sport Exerc. 40(2):275-81. doi: 10.1249/mss.0b013e31815adf19.
Pugh JN, et al. (2019) Four weeks of probiotic supplementation reduces GI symptoms during a marathon race. Eur J Appl Physiol. In press (Apr 13). doi: 10.1007/s00421-019-04136-3.
AUTHOR
Pedro Valenzuela
Researcher in the Physiology Unit of the University of Alcalá and in the Performance Control Unit at the Sports Medicine Center (AEPSAD, CAR of Madrid).
Web: www.fissac.com
