Training the Gut for Athletes

Abstract

The gastrointestinal (GI) tract plays a critical role in delivering carbohydrate and fluid during prolonged exercise and can therefore be a major determinant of performance. The incidence of GI problems in athletes participating in endurance events is high, indicating that GI function is not always optimal in those conditions. A substantial body of evidence suggests that the GI system is highly adaptable. Gastric emptying as well as stomach comfort can be “trained” and perceptions of fullness decreased; some studies have suggested that nutrient-specific increases in gastric emptying may occur. Evidence also shows that diet has an impact on the capacity of the intestine to absorb nutrients. Again, the adaptations that occur appear to be nutrient specific. For example, a high-carbohydrate diet will increase the density of sodium-dependent glucose-1 (SGLT1) transporters in the intestine as well as the activity of the transporter, allowing greater carbohydrate absorption and oxidation during exercise. It is also likely that, when such adaptations occur, the chances of developing GI distress are smaller. Future studies should include more human studies and focus on a number of areas, including the most effective methods to induce gut adaptations and the timeline of adaptations. To develop effective strategies, a better understanding of the exact mechanisms underlying these adaptations is important. It is clear that “nutritional training” can improve gastric emptying and absorption and likely reduce the chances and/or severity of GI problems, thereby improving endurance performance as well as providing a better experience for the athlete. The gut is an important organ for endurance athletes and should be trained for the conditions in which it will be required to function.

Key Factors Influencing the Food Choices of Athletes at two Distinct Major International Competitions

“…Gut discomfort has also been reported as a significant issue for endurance athletes such as triathletes [5] and ultra-endurance athletes [4]. Recent literature has reported improved gastrointestinal comfort with lower FODMAP (fermentable oligo-, di-, mono-saccharides and polyols) intake in athletes [27][28][29][30], and this may be an emerging consideration by some individuals. There were mixed responses about concerns for positive doping influencing food choice.…”

Contemporary Nutrition Strategies to Optimize Performance in Distance Runners and Race Walkers

“…For example, workouts/ (Jeukendrup, 2017a). Furthermore, when intake during the event is beneficial, it may be possible to prepare the gut to optimize and tolerate this by practicing strategies with adjusted intakes of CHO and fluid within the training sessions (Jeukendrup, 2017b). It is likely that the heavy training loads and habitual dietary practices of high-performance distance runners/walkers, including the remarkable East African athletes (Commentary 1), already create periodization of CHO availability across a training cycle.…”

“…The limiting factor was subsequently found to be intestinal absorption, particularly the sodium-dependent glucose transporter, rather than gastric emptying, hepatic glucose extraction, muscle glucose uptake, or muscle glucose oxidation (Jeukendrup, 2014). However, as reviewed by Jeukendrup (2017b), sodium-dependent glucose transporter abundance and activity in animals is increased by a CHO-rich diet; furthermore, chronic exposure to higher CHO intakes by athletes, including exercise intake, increases gut tolerance, intestinal absorption, and muscle oxidation of CHO consumed during exercise Cox et al, 2010). Combining glucose-based CHO sources with fructose (transported in the intestine by GLUT5) increases total exogenous CHO oxidation during exercise, with rates as high as 1.75 g/min (Jeukendrup & Chambers, 2010).…”

Sports Nutrition and Performance

“…These gastrointestinal problems may be due to the redistribution of blood flow to the muscles during exercise. Therefore, strategies for bowel training have been proposed to increase the rate of gastric emptying as well as reduce possible discomfort [21]. When it is proposed to reach recommendations, it seems beneficial to alternate different types of drinks, gels, or bars, so that the taste is not monotonous.…”

“…In general, the rate of sweating is usually greater than that of gastric emptying. However athletes can be trained to increase gastric emptying during workouts and thereby reduce dehydration as possible [21]. In conditions of higher temperature and humidity, this rate of sweating will rise higher.…”