In order to minimize energy deficit and limit the use of glycogen reserves during ultra-endurance events, appropriate, sufficient and regular hydration and nutrition throughout the effort will be essential and decisive elements.
In ultra-endurance athletes, gastrointestinal disorders (GIDs) are extremely common and represent the leading cause of withdrawal from races.
On average, between 30% and 50% of marathon runners experience digestive issues, a prevalence that climbs to 83% for 60km races and even reaches 96% for 161km ultramarathons ( Source ). These issues include both upper gastrointestinal problems such as heartburn, nausea, and vomiting, and lower gastrointestinal problems such as abdominal pain, urgency, and diarrhea. These symptoms, in most cases, will worsen with increasing duration and under particularly challenging conditions: high temperatures, high humidity, and high altitude. In the most severe cases, this can lead to hospitalization.
Origins and explanations of Gastrointestinal Disorders:
Firstly, we can note the mechanical constraints linked to the activities practiced (for example, repeated impacts in disciplines such as running, trail running…) which lead to a release of prostaglandins and intestinal peptides resulting in an acceleration of intestinal motility.
In addition to mechanical factors, circulatory factors can also contribute to gastrointestinal distress (GID). Indeed, the reduction in splanchnic blood flow associated with exertion leads to ischemia (lack of oxygen) of the digestive tract, thus limiting digestive function. It is important to keep in mind that this phenomenon is exacerbated in cases of dehydration. During intense exercise, the reduction in blood flow to the digestive system can reach up to 80%, which significantly limits the absorption of ingested nutrients.
The lack of oxygenation of the digestive system as well as the secretion of certain anorexigenic hormones completely inhibits the sensation of hunger in most athletes.
Above 70% of VO₂ max, abdominal blood flow decreases significantly and is redirected to the muscles requiring more oxygen. Depending on the intensity, duration, and effort management, solid foods can be extremely difficult, or even impossible, for some athletes to chew and swallow, potentially causing or exacerbating digestive problems. If solid food is inedible, athletes should consider liquid or semi-liquid solutions to ensure adequate nutrition. Gels are therefore good alternatives for providing sufficient carbohydrates. With appropriate testing and a gradual increase in carbohydrate intake during exercise, high doses of carbohydrates (up to 1.4 g/min) are generally well tolerated.
Strategies such as the simultaneous ingestion of glucose and fructose (each molecule using different transporters in the intestine) can increase carbohydrate oxidation by 1 to 1.26 g/min due to improved bioavailability. Therefore, glucose or glucose-fructose gels are generally well-tolerated; however, some athletes may still experience digestive symptoms. This is why multiple tests during intensive training and under conditions similar to those of races are essential to train the digestive system.
Finally, it is essential to remember that taking non-steroidal anti-inflammatory drugs will be strongly discouraged, as in most cases they worsen symptoms by reducing the mucoprotective film and increasing acid secretions, leading to greater intestinal permeability.
Nutritional strategies to prevent IBS:
-
Limit your intake of fiber and fat : Foods high in fat and fiber take much longer to digest, thus increasing the risk of gastrointestinal distress during prolonged exertion. Therefore, around and during long events, it is essential to focus your food choices on easily digestible foods, primarily rich in carbohydrates (applesauce, bananas, refined starches, etc.) and lean protein.
-
Adjusting carbohydrate intake : Carbohydrate intake between 60 and 90 g per hour is recommended for events lasting more than three hours, with a glucose:fructose ratio of 2:1. The combination of the two carbohydrates uses different transporters in the intestine, which allows for more efficient absorption and reduces the risk of digestive problems related to transporter saturation.
-
Testing strategies beforehand : Since each athlete has a different digestive tolerance, it is recommended to test nutritional strategies several times during training to avoid any surprises on race day. "Gut training," which involves progressively increasing carbohydrate intake during varying levels of exertion and in all situations, should be implemented to help the digestive system adapt to high carbohydrate and fluid volumes under physical stress. Although the evidence is still developing, it has been shown that intestinal carbohydrate transporters can be modulated by training, and that gastric emptying also improves with training. Discover Foundation, the first supplement dedicated to the gut health of endurance athletes.
Conclusion
Digestive disorders (GD) are a very common performance bottleneck for ultra-endurance athletes. The causes are varied, ranging from dehydration and poor carbohydrate management to mechanical and circulatory stresses. However, the risk of developing digestive problems can be minimized through careful adjustment of fluid and nutritional intake around and during exercise, as well as through nutritional testing during training. "Gut training" appears to be a promising solution, offering athletes better tolerance to energy intake and optimized performance during the most demanding events.
Sources:
