## 4 Discussion
Such changes were not observed in the CON group; however, the diet's nutritional value was much higher, and the level of markers was lower than in CVD subjects. While GST and GPx are involved in maintaining cellular homeostasis and protecting against harmful substances, their specific enzymatic activities and substrate specificities differ. GST primarily focuses on detoxification pathways, while GPx is primarily responsible for protecting cells from oxidative damage. The GSTs are structurally highly diverse enzymes protecting against reactive \(\alpha\),\(\beta\)-unsaturated carbonyls, epoxides, and hydroperoxides produced in vivo as the breakdown products of macromolecules during oxidative stress [52; 53; 54]. Changes in GST levels induced by a diet high in glucosinolates have already been observed by other authors, who noted an increase in GST levels after a 3-week consumption of 300g of cooked Brussels sprouts per day [55; 56]. In our study, changes in GST concentrations were induced by betalains and anthocyanins present in red beetroot and chokeberry. In contrast, the lack of change in GST concentration in the control group, in which oxidative stress levels were probably lower and the diet better balanced, seems interesting but explainable. We suggest that changes in the glutathione-related antioxidant defence system will be related not only to the dose and type of dietary antioxidants consumed in the diet but also to the initial antioxidant capacity of the body. Additionally, of interest, in terms of the outcome of the dietary intervention, were the changes in glutathione peroxidase (GPx) levels induced by the same dietary intervention. We observed a significant increase (\(p<0.01\)) of GPx in the CVD group, but no changes in the CON group. GPx catalyses the reduction of H\({}_{2}\)0\({}_{2}\) and organic hydroperoxides to water and alcohol by generating GSSG (glutathione disulfide). Several distinct families of enzymes have evolved that display GPx activity. These have been classified as selenium-dependent or selenium-independent [57]. Our results present GPx concentration before DI can be compared with those existing in the literature [58]. Additionally, an increase in GPx activity under the influence of nutritional interventions with Brazilian nuts corresponded to those obtained in our experiment during snacking with chokeberry juice and beetroot crisp [58]. The Brazilian authors explained that th increased GPx concentration was due to the increased erythrocyte selenium levels [58]. In our study, we did not identify any rich source of selenium. In our study, we selected two snacks recognised as healthy and recommended by the CVD Polish patients. We confirmed this popularity and willingness to snack during the qualification stage. These snacks are commonly consumed by individuals with cardiovascular disease (CVD). Although the beetroot crisps had a lower antioxidant capacity than aronia juice, they were more widely favoured as a vegetable among the Polish population. Though the popularity and presence of aronia juice on the market is apparent, its sensory acceptability is meaningfully lower because of its tart taste. Additionally, the antioxidative properties of both snacks differed and were related to different compound classes. The beetroot crisps mainly contain high content of betalains, while the chokeberry juice contains mainly flavonoids. Since we planned to evaluate the general effect of diet supplementation and increased general diet antioxidant capacity on the pilot level of study, betalains and flavonoids were chosen as both classes have a beneficial effect on the cardiovascular system [59; 60; 61]. Dietary antioxidant capacity is perceived as a new pro-healthy indicator of diet quality and has been studied previously in CVD and prediabetes group [62; 63]. Those studies showed that higher dietary antioxidant capacity was associated with glutathione-related antioxidant defence system changes.