Training the Gut for Athletes

Repetitive Feeding-Challenge With Different Nutritional Densities on Markers of Gastrointestinal Function, Substrate Oxidation, and Endurance Exercise Performance

Gut-training has been shown to improve gastrointestinal tolerance, circulatory glucose availability, and exercise performance. The study aimed to investigate the effects of a repetitive feeding-challenge using fat versus carbohydrate (CHO) on markers of gastrointestinal function, glucose availability, and subsequent performance when challenged with a high-CHO load (87 g/hr) during exercise. Forty-four endurance athletes (mean ± SD [9 females and 35 males]: body mass: 71.2 ± 9.2 kg, height: 173.6 ± 7.0 cm, V˙O2max: 55.0 ± 6.1 ml·kg-1·min-1) completed a preintervention gut-challenge trial (T1), involving a 2 hr run (60% V˙O2max) while taking a CHO gel every 20 min (87 g/hr, 10% w/v), followed by a 1 hr self-paced distance test with ad libitum water. Participants were then randomized to a fat (fat feeding-challenge [FFC]; 20 g nut butter, 124 kcal, 11 g fat, 3 g protein, and 3 g CHO) or CHO supplement (CHO feeding-challenge [CFC]; 47 g CHO gel: 123 kcal, 29 g CHO) group to complete a 7-day repetitive feeding-challenge (1 hr exercise and supplement intake every 20 min with 290 ml water), followed by a gut-challenge retrial (T2). FFC did not differ from CFC in terms of resting orocecal transit time, feeding tolerance, or substrate oxidation during T1 and T2. Peak breath hydrogen was lower in FFC than CFC (p = .028) at T2. Total (FFC: 27%, p = .005 vs. CFC: 38%, p = .001) and upper gastrointestinal symptoms severity (FFC: 26%, p = .013 vs. CFC: 40%, p < .001) during exercise was reduced similarly between groups from T1 to T2. FFC covered more distance in T2 (11.51 ± 2.02 vs. 11.08 ± 2.02 km, p = .013), but not significantly different to CFC (p = .341). A repetitive feeding-challenge with fat does not enhance nor worsen gastrointestinal and fueling outcomes compared with a CHO repetitive feeding-challenge.

The Effect of Gut-Training and Feeding-Challenge on Markers of Gastrointestinal Status in Response to Endurance Exercise: A Systematic Literature Review

BACKGROUND

Nutrition during exercise is vital in sustaining prolonged activity and enhancing athletic performance; however, exercise-induced gastrointestinal syndrome (EIGS) and exercise-associated gastrointestinal symptoms (Ex-GIS) are common issues among endurance athletes. Despite this, there has been no systematic assessment of existing trials that examine the impact of repetitive exposure of the gastrointestinal tract to nutrients before and/or during exercise on gastrointestinal integrity, function, and/or symptoms.

OBJECTIVE

This systematic literature review aimed to identify and synthesize research that has investigated the impact of 'gut-training' or 'feeding-challenge' before and/or during exercise on markers of gastrointestinal integrity, function, and symptoms.

METHODS

Five databases (Ovid MEDLINE, EMBASE, CINAHL Plus, Web of Science Core Collection, and SPORTDiscus) were searched for literature that focused on gut-training or feeding-challenge before and/or during exercise that included EIGS and Ex-GIS variables. Quality assessment was conducted in duplicate and independently using the Cochrane Collaboration's risk-of-bias (RoB 2) tool.

RESULTS

Overall, 304 studies were identified, and eight studies were included after screening. Gut-training or feeding-challenge interventions included provision of carbohydrates only (n = 7) in various forms (e.g., gels or liquid solutions) during cycling or running, or carbohydrate with protein (n = 1) during intermittent exercise, over a varied duration (4-28 days). Gut discomfort decreased by an average of 47% and 26% with a 2-week repetitive carbohydrate feeding protocol (n = 2) and through repeated fluid ingestion over five trials (n = 1), respectively. Repetitive carbohydrate feeding during exercise for 2 weeks resulted in the reduction of carbohydrate malabsorption by 45-54% (n = 2), but also led to no significant change (n = 1). The effect of gut-training and feeding-challenges on the incidence and severity of Ex-GIS were assessed using different tools (n = 6). Significant improvements in total, upper, and lower gastrointestinal symptoms were observed (n = 2), as well as unclear results (n = 4). No significant changes in gastric emptying rate (n = 2), or markers of intestinal injury and permeability were found (n = 3). Inconclusive results were found in studies that investigated plasma inflammatory cytokine concentration in response to exercise with increased carbohydrate feeding (n = 2).

CONCLUSIONS

Overall, gut-training or feeding-challenge around exercise may provide advantages in reducing gut discomfort, and potentially improve carbohydrate malabsorption and Ex-GIS, which may have exercise performance implications.