Carbohydrates are an important source of energy for the human body. Carbohydrates make a positive contribution to the period in which an effort can be sustained and thus to physical performance. Athletes are advised by the American College of Sports Medicine to take between 30 and 60 grams of carbohydrate per hour during prolonged exercise. Others even advise during workouts longer than two hours an intake to 90 grams of carbohydrate per hour.

Unfortunately, there are not only positive effects on carbohydrate intake; ingestion can also lead to complaints of the gastro-intestinal tract. Researchers have studied the carbohydrate intake and the prevention of gastro-intestinal complaints in endurance athletes.

A total of 221 participants (180 men and 41 women) from the following sports participated in the study;

Ironman (n = 107),
Half Ironman (n = 43),
Two 200 km cycling races (42 professional cyclists),
120 km cycling race (20 amateur cyclists),
Marathon (n = 12).

Carbohydrate intake and gastrointestinal symptoms that were experienced were asked by means of questionnaires.

The results show that the largest amounts of carbohydrates were taken during Ironman races (average 62, 65 and 71 grams per hour). During amateur cycling, this was significantly lower with an average of 53 grams per hour. The least carbohydrates were taken during the marathon; an average of 35 grams per hour. There are more carbohydrates taken during cycling than during running. Carbohydrate intake differed greatly between all participants; of 6 grams per hour to 136 grams per hour. The authors found that a high carbohydrate intake often corresponded with the best rankings.

What is clear is that a high carbohydrate intake can cause nausea and flatulence.

Nauseous and vomit
Bowel problems and diarrhea

It must be said that it often involves people who are susceptible to this type of gastrointestinal complaints. A guideline does not have to be appropriate for each individual. Try to experiment first during training with different amounts of carbohydrate intake. In this way, the optimal amount of carbohydrates can be taken during competitions without this leading to gastro-intestinal complaints.



Asker Jeukendrup from Birmingham presented the current advice for discussion of taking 30-60 grams of carbohydrate per hour during exercise. Jeukendrup proposes to allow an intake to 90 grams of carbohydrate per hour. The intake of 30 grams of fructose in addition to the 60 grams of glucose namely leads to a higher intake than 60 grams carbohydrate per hour. The explanation is in accordance with Jeukendrup in the transport systems in the gastrointestinal tract which transport the carbohydrates into the blood. These become saturated if the carbohydrate intake is limited to one type of carbohydrate.

The combined intake of two types of carbohydrates uses different transport systems and then the carbohydrate intake can rise up to 90 grams per hour. This opinion according Jeukendrup is independent of the body weight of an athlete. Canadian food scientist Trent Stellingwerf suggests that athletes can train their transport systems for the various carbohydrates.

Stellingwerf also briefly touched on the “stacking” of carbohydrates before a race. Per gram of carbohydrate 2.8 grams of water is stored. This therefore leads to an additional increase in the body weight which is not desirable in all race situations.