Ultra-endurance events demand extreme physical and mental preparation. But these aren't the only determining factors for performance. Among the other fundamental elements is nutrition, which is also crucial for maintaining sufficient energy levels throughout the entire effort.
Alongside the increase in exertion time, athletes are forced to increase their nutritional intake in order to maintain performance and delay the onset of fatigue. This increase in nutritional intake requires athletes to have a very good capacity for nutrient assimilation in order to avoid being limited by gastrointestinal disorders, which are extremely common in long events exceeding 4 hours of exertion [ Nutritional intake and gastrointestinal problems during competitive endurance events ].
This assimilation capacity can, however, be affected by a syndrome that affects many ultra-endurance athletes: intestinal permeability, or "leaky gut".
What is the gut microbiota?
The human gastrointestinal tract harbors a vast and diverse community of microorganisms, including bacteria, archaea, fungi, viruses, and other eukaryotes. This community of microorganisms is collectively known as the "gut microbiota." The gut microbiota plays a crucial role in human health by providing metabolic, immune, and protective functions through its symbiotic relationship with its host.
This microbiota is essential for a multitude of processes, including nutrient breakdown, vitamin production, and the modulation of the immune response. Its health is particularly important for ultra-endurance athletes, as a balanced and functional microbiota will allow for proper nutrient absorption and help prevent the risk of gastrointestinal disturbances during exercise.
Sources: Bidell, MR, Hobbs, ALV, Lodise, TP: Gut microbiome health and dysbiosis: A clinical primer. Pharmacotherapy, 2022 Thursby, E., Juge, N.: Introduction to the human gut microbiota. Biochem. J. (2017).
Introduction to prebiotics
Prebiotics are non-digestible food substances that promote the growth and activity of beneficial bacteria in the gut, particularly bifidobacteria and lactobacilli. These components generally resist digestion in the upper gastrointestinal tract and are not broken down by human digestive enzymes, allowing them to reach the colon, where they serve as a substrate for fermentation by the gut microbiota. Prebiotics are found in certain foods such as onions, garlic, leeks, asparagus, bananas, oatmeal, barley, wheat bran, and legumes.
Intestinal permeability: an obstacle to nutrient absorption
During prolonged endurance events, gastrointestinal disturbances (GI distress) frequently occur, notably due to splanchnic ischemia, which reduces blood flow to the intestines by 30 to 40% when the intensity of the effort exceeds 70% of VO2 max ( Association of gastrointestinal distress in ultramarathoners with race diet ). This phenomenon leads to decreased oxygenation of the intestinal mucosa, causing inflammation and increased intestinal permeability. This phenomenon, known as "leaky gut," compromises the intestinal barrier, allowing toxins and undigested food particles to pass into the bloodstream, potentially leading to systemic inflammation and severe gastric disturbances. These digestive issues, including nausea, cramps, and vomiting, generally affect more than half of ultramarathon runners. (Source: Stuempfle KJ, Hoffman MD, Weschler LB, Rogers IR, Hew-Butler T. Race diet of finishers and non-finishers in a 100 mile (161 km) mountain footrace .)
Factors influencing intestinal permeability
The phenomenon of intestinal hyperpermeability (IP) is defined as a weakening of the lining of the small intestine which, by becoming porous, allows the passage of nutrients, bacteria and waste that should not be able to pass through this intestinal barrier.
Intestinal permeability can be influenced by various factors, including changes in the gut microbiota, chronic stress, the use of nonsteroidal anti-inflammatory drugs (NSAIDs), alcohol consumption, infections, and certain medical conditions. These factors weaken the intestinal barrier, thus increasing intestinal permeability and the susceptibility to inflammation and gastrointestinal disorders. Lifestyle and dietary habits also play a significant role in the development of this phenomenon. Source: Bischoff, SC, Barbara, G., Buurman, W., Ockhuizen, T., Schulzke, J.-D., Serino, M., Tilg, H., Watson, A., Wells, JM: Intestinal permeability – a new target for disease prevention and therapy. BMC Gastroenterol. 14 (1) (2014) .
Ultra-endurance athletes are particularly susceptible to the risk of intestinal permeability due to the mechanical and physiological stresses associated with exertion (impacts, ischemia of the digestive system, etc.). It is therefore essential for these athletes to take extremely good care of their digestive system and adapt their diet to maintain optimal intestinal mucosa.
The importance of prebiotics and probiotics in optimizing assimilation capacity
To combat the risks of gastrointestinal disorders, research is increasingly focusing on the daily use of prebiotics, probiotics, and postbiotics that help improve intestinal health, reduce intestinal permeability, and consequently optimize nutrient absorption.
By strengthening the intestinal barrier, probiotics not only help reduce the risk of IBS, but also increase the absorption capacity of essential nutrients, which is vital for ultra-endurance athletes who rely on a constant supply of energy to maintain their performance.
Reducing TGI to maintain constant energy intake
Gastrointestinal disorders (GI disorders) are not just uncomfortable; they are the number one reason for dropping out of endurance events. These disorders are more prevalent in running events ( Learn all about the origins of GI disorders ) compared to other endurance activities, due to the repeated impact on the ground. Research shows that prebiotics , by stimulating the production of butyrate, a short-chain fatty acid that strengthens the intestinal barrier, can improve intestinal tolerance and thus reduce the frequency and severity of GI disorders. Improved digestive tolerance allows athletes to continue fueling, thereby reducing the energy deficit often observed in ultra-endurance events.
Sources: Stuempfle KJ, Hoffman MD. Gastrointestinal distress is common during a 161-km ultramarathon. J Sports Sci. 2015 https://www.mdpi.com/2072-6643/15/20/4330
Prebiotics and probiotics: allies against dehydration and fluid overload
Another important factor is fluid balance. Inadequate hydration, whether through dehydration or overhydration, increases the risk of gastrointestinal distress (GID), notably by contributing to hyponatremia and splanchnic hypoperfusion. Regular consumption of prebiotics and probiotics may help maintain this fluid balance by reducing intestinal inflammation and improving the digestive system's tolerance to fluid fluctuations. Studies have shown that athletes with adequate hydration and a balanced gut microbiota are less prone to electrolyte disturbances and GID during endurance events. Sources: Wasse LK. Importance of gastrointestinal function to athletic performance and health https://www.mdpi.com/2072-6643/16/5/744 .
Adapting nutritional strategy through a healthy microbiota
Beyond reducing GI tract infections, a healthy gut microbiota also helps optimize nutritional strategy. While general recommendations for ultra-endurance athletes suggest consuming between 60 and 90g of carbohydrates per hour to maintain peak performance, many runners, even well-trained ones, struggle to reach these intakes (Source: Kenchtle B, Bisig A, Schlapfer F, Zwyssig D. Energy metabolism in long-term endurance sports: a case study. Praxis. 2003 ). Therefore, improved nutrient absorption through enhanced gut health would allow these athletes to get the most out of every bite or sip.
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Conclusion: Investing in gut health leads to optimal performance.
In the context of ultra-endurance events, where physical and mental limits are tested, the body's ability to assimilate the nutrients provided is a decisive factor.
Intestinal permeability, a phenomenon exacerbated by mechanical stress and intense exertion, remains a major obstacle to the efficient absorption of nutrients. Incorporating prebiotics and probiotics appears to be an effective solution for strengthening the intestinal barrier, reducing the risk of gastrointestinal upset, and optimizing nutrient absorption. This nutritional strategy, focused on gut health, is becoming an essential pillar for athletes seeking to reach their full potential during these extreme events.
