The Effect of Newly Designed High-Antioxidant Food Products on Oxidative Stress and Antioxidant Markers in Athletes

The aim of this study was to develop functional food with high antioxidant potential and to examine its effect on oxidative–antioxidant markers in the blood of athletes in an intervention study. The study population consisted of 40 athletes—long-distance runners who were divided into a study group (SG) and a control group (CG). Before and after the dietary intervention in the blood, the following were determined: total antioxidant status (TAS), antioxidant enzymes (superoxide dismutase—SOD, glutathione peroxidase—GPx, catalase—CAT) and total oxidative stress (TOS). Additionally, the oxidative stress index (OSI) was calculated. It was shown that in the SG after the dietary intervention, the TOS (p < 0.001) and OSI (p = 0.029) decreased, while the TAS increased (p < 0.001). However, no significant differences were found in the level of antioxidant enzymes in the SG. In the CG, dietary intervention did not affect the level of the assessed parameters. This study demonstrated that functional food in the form of a bar with high antioxidant potential, rich in polyphenols, dietary fiber, vitamin E, selenium, and magnesium, can support the body’s endogenous antioxidant system and restore oxidative–antioxidant homeostasis in athletes. However, further studies are needed, including a larger group of athletes, longer intervention times, and different periods of the annual training cycle.