Local and Systemic Effects of Flavonoid Intake With Submaximal Cycling Exercise: A Randomized Controlled Trial

Moderate to high intensity endurance exercise is a known cause of exercise-induced gastrointestinal syndrome, a condition often associated with intestinal complaints such as discomfort, cramps, and diarrhea. Oftentimes, elevated intestinal inflammation and permeability (a “leaky gut”) are also observed. Previous research has shown that flavonoids, natural compounds found in many fruits and vegetables, may mitigate these exercise-induced effects. In particular, certain cocoa powders contain high levels of flavonoids, and chocolate milk is a good source of protein and sugars for sustaining intense activity. Thus, the purpose of this study was to evaluate the effects of a dairy pre-workout beverage, with flavonoids from cocoa, blueberries, and green tea. We hypothesized that regular consumption of these flavonoids would alleviate exercise-induced gastrointestinal syndrome. A clinical trial was conducted with twelve subjects, who consumed the pre-workout once per day. After 14 days, subjects completed a one-hour cycling test to determine the effects of the beverage on performance and gastrointestinal health. Each participant underwent both the treatment and control in a randomized order, serving as his or her own control for comparison. Our results showed that the cycling trial was strenuous and caused measurable changes in biomarkers of inflammation and intestinal injury, but ultimately, the flavonoid pre-workout did not differ from the control. These findings suggest that short-term flavonoid supplementation from processed food ingredients (cocoa powder, freeze-dried blueberries, and powdered green tea) may not have protective effects on the gut during exercise-induced stress. However, the product was well-liked by the subjects and no negative effects were observed. Nutritional strategies for reducing incidence of exercise-induced gastrointestinal syndrome is a relatively new area of research, and these results can help shape future recommendations in sports nutrition for endurance athletes and coaches. This project contributes to current scientific knowledge regarding the interaction between flavonoid consumption and intestinal health. Furthermore, similar mechanisms are thought to drive related conditions such as exertional heat stress, ulcerative colitis, and inflammatory bowel disease. Due to the prevalence of a leaky gut and inflammation in not only endurance exercise but also these other conditions, more research—especially well-controlled human clinical trials—is warranted