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Who doesn’t know the troublesome gastrointestinal problems that occur precisely during the most important training unit or competition?

This article is presented by the Swiss Sports Nutrition Society

On the whole, it is estimated that 30 to 50% of all athletes struggle with such problems on a regular basis. There are various reasons as to why or how they occur or materialise. Before developing strategies to prevent these problems, an individual analysis of the underlying causes must first be made. It is well-known that various nutritional components more frequently lead to problems in the gastrointestinal area than others. Dietary fibres, fat and highly concentrated carbohydrate solutions seem to be particularly common causes. This usually leads to bloating, cramping or even diarrhoea. One way to combat these symptoms is to train the gastrointestinal tract in terms of gastric emptying, nutrient uptake, and volume.

Gastric emptying

The gastric emptying rate is the time it takes food to leave the stomach and reach the small intestine. The emptying speed is higher when more fluid is present in the stomach. However, other factors, such as energy density, osmolarity or the training load also influence gastric emptying. Studies have shown that targeted dietary intervention - such as a high carbohydrate intake via gels or high fluid intake – could improve the gastric emptying rate and also reduce the symptoms during the load.

Carbohydrate intake in the intestine

As soon as carbohydrates reach the intestine along with other nutrients or water, they are transported through specific transport channels into the bloodstream. There are channels that are specialised in the transport of glucose and others that are specialised in the transport of fructose. One of these various transport channels, which transports glucose, can transport a maximum of 1 g of carbohydrates per minute, i.e., 60 g per hour. For this reason, it is important to resort to fructose and glucose for a higher intake of carbohydrates (60 to 90 g per hour). Studies have also shown that athletes who consume carbohydrates through their daily food intake have a better gastric emptying rate and can absorb carbohydrates in the intestine more efficiently.

Practical application

Those who restrict their intake of carbohydrates in everyday life as well as during training units run the risk of deteriorating the absorption capacity of carbohydrates in the intestine. If you ultimately still want to consume the recommended amount of carbohydrates (60 to 90 g per hour for competitions with a duration of >120 min) during the competition, this can lead to gastrointestinal problems. The body is no longer used to this amount of carbohydrates within such a short time. Thus, if an athlete is on a “low-carb” or “ketogenic” diet, they are recommended incorporating a few carbohydrate-rich days into their training before the competitions. It is also worth testing your competition nutrition during training and train as described above. This means that the target product must be tested at the correct dosage (in this example 60 to 90 g per hour). It is worth gradually increasing the dosage until the target dose is reached. This means starting at 20 g per hour and increasing it from training to training until you can tolerate up to 60 to 90 g per hour under the intensity of a competition. A combination of glucose and fructose or maltodextrin and fructose is recommended at such high doses. You should also train your fluid intake, especially when high sweat rates (e.g., in heat and humidity) are expected and thus a higher consumption of fluids during the competition.

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