Endurance training (intense exercise for more than an hour at 70% of maximum work capacity) induces changes to intestinal structure and functionality - increasing intestinal permeability and sensitivity to pathogenesis.
While low-to-moderate exercise has shown positive effects on the gastrointestinal (GI) health, athletes at the high-end (such as marathon runners) can experience acute GI disorders with a negative impact on health status and performance.
This can lead to reduced gastric motility, epithelial injury, disturbed mucosa integrity, impaired nutrient absorption, endotoxemia, and both local and systemic low-grade inflammation, researchers explain in Nutrients.
“The intestinal barrier has a critical function in human health, with a role in the pathogenesis of intestinal and systemic diseases. Because of the downregulation of intestinal adhesion proteins induced by gut dysbiosis, lipopolysaccharides (LPS) caused increases in reactive oxygen species (ROS) production and translocated into the systemic circulation can elicit an inflammatory response that may contribute to atherosclerotic damage, clotting activation, and thrombus formation.”
A recent study on resistance-trained men, found greater lactulose–rhamnose (L/R) ratio and intestinal fatty acid-binding protein (I-FABP) levels (both measures of intestinal cellular injury) in post-exercise males, compared with non-exercise controls.
Furthermore, molecular and physiological changes were noted in gut permeability of athletes in several sports, including swimming and running.
Dietary polyphenols exert powerful antioxidant action. They increase abundance of short-chain fatty acid-producing bacteria that alleviates intestinal oxidative stress, restores microbiota diversity, and improves inflammatory status and intestinal barrier function.
Nevertheless, there is a dearth of studies on the effects of polyphenol supplements in exercise-induced gut dysfunction, and none on outcomes with polyphenol-rich foods on intestinal permeability in athletes.
“Despite evidence, more studies are needed to highlight the role of exercise in intestinal permeability and to identify other variables that may influence this phenomenon,” they say.
“It is important to identify effective non-invasive strategies that are able to modulate intestinal permeability. In general, there is growing evidence that dietary supplementation with polyphenols derived from natural products can improve physical performance, with mechanisms that are most likely related to antioxidant and vascular effects.”
Researchers examined the effects of polyphenol intake on biomarkers for intestinal barrier integrity and gut microbiome. They found that chronic intake of polyphenols (40g) for 30 days positively modulated exercise-induced damage from elevated LPS and restored intestinal barrier integrity in elite football players.
Twenty-four elite male athletes and 23 amateurs were recruited for the study. Elite athletes were members of the Italian first-league A.S. Roma youth team who trained 14 hours per week, and with a least eight years of competitive experience. The 23 amateur subjects performed moderate-to-intense physical activity three days a week.
A comparison of gut permeability between the groups was determined by measuring levels of three biomarkers for changes in intestinal barrier integrity (LPS, zonulin, and occludin).
Of the elite cohort 12 were randomly assigned a dark chocolate tablet (85% cocoa) for 30 days, plus a normal diet, and 12 were controls. Total polyphenol content in the tablets was 799 μg GAE/mL, and epicatechin and catechin of 0.65 mg/g and 0.26 mg/g, respectively. Blood content of the biomarkers was assessed at baseline and 30 days after the last ingestion of chocolate.
In vitro tests were carried out to analyse the protein system essential for barrier integrity and to substantiate the clinical effects of cocoa-derived polyphenols on gut permeability.
Biomarkers of gut permeability were significantly higher in elite athletes compared to the amateurs at baseline, while correlation analysis determined that LPS was associated with both zonulin and occulin.
The control group experienced increased LPS after 30 days of training along with increased zonulin and occludin, compared to baseline. Conversely, there was no change to biomarker levels in the elite group taking supplementation.
In vitro data confirmed that LPS increased oxidative stress, destroying intestinal cell integrity. However, cell viability remained unchanged in the presence of polyphenol extracts, indicating no cytotoxic effect on Caco-2 cells (intestinal barrier).
The authors add: “Polyphenols from dark chocolate are active natural products with excellent antioxidant and anti-inflammatory properties that effectively protected intestinal cells against LPS induced injury. These results suggest that polyphenol-rich foods such as dark chocolate may be effective adjuvants for preventing LPS-associated intestinal damage in football athletes.”
Published online September 28, 2023: http://doi.org/10.3390/nu15194203
“Dark Chocolate Intake Positively Modulates Gut Permeability in Elite Football Athletes: A Randomized Controlled Study”
Authors: Cristina Nocella, Elena Cavarretta, Chiara Fossati, Fabio Pigozzi, Federico Quaranta, Mariangela Peruzzi, Fabrizio De Grandis, Vincenzo Costa, Carwyn Sharp, Massimo Manara, Antonia Nigro, Vittoria Cammisotto, Valentina Castellani, Vittorio Picchio, Sebastiano Sciarretta, Giacomo Frati, Simona Bartimoccia, Alessandra D'Amico and Roberto Carnevale