## 1 Introduction  
Chronic diseases such as obesity, type 2 diabetes mellitus (T2D), metabolic syndrome (MetS), and atherosclerosis, the prevalence of which has increased over the last couple of years, are related to the postprandial state, as postprandial glycemia and lipidemia are critically linked to their onset. Western lifestyle diets lead to the postprandial increase of glucose, triglycerides, and insulin and, therefore, to the induction of postprandial oxidative stress [1]. The consumption of either a high-fat or high-carbohydrate diet or even a combination of both can elicit postprandial inflammation and, hence, the generation of reactive oxygen species (ROS). Oxidative stress-induced damage and inflammation have been reported to play a significant role in the pathogenesis of chronic diseases [2]. Therefore, there is a growing demand for functional food products as the chronic diseases described above can be targeted through a healthy nutrition plan. Functional foods incorporated into a daily nutrition plan could decrease the risk of chronic diseases through the supplementation of bioactive compounds [3]. Over the years, studies have provided evidence for the protective effects of various polyphenol-rich foods against chronic diseases. Fruits and cereals are rich in phenolic compounds, while grape seeds represent rich sources of polyphenols. Proanthocyanin, anthocyanins, flavonols, phenolic acids, and stilbenes are the main phenolic compounds found in grapes [4]. The bioavailability of dietary polyphenols, including those present in grapes, has been broadly reported [5; 6]. Following ingestion, polyphenols are detected in plasma, interacting with lipoproteins [7]. They represent potent antioxidants as their ability to inhibit risk factors such as hyperlipidemia, hyperglycemia, inflammation, and hypertension, which are involved in chronic diseases such as diabetes and metabolic syndrome, has been broadly reported [8; 9; 10]. Grape seed contains the majority of polyphenols, including mainly proanthocyanin-dins [11], which have been studied for a number of health properties, such as their antioxidant and free-radical scavenging activity, as well as their potential to be used as nutritional supplements for atherosclerosis and cardiovascular disease prevention and in dyslipidemia treatment. There are also many studies indicating gastro-protective, hepato-protective, and anti-obesity effects of grape polyphenols [12; 13; 14]. Grape seed flour is a novel exploited flour that possesses a high fiber content and antioxidant capacity due to its rich phenolic content, which includes phenolic acids, flavonoids, and proanthocyanin [15]. In many scientific studies, grape seed flour has been used for bakery product fortification in, for example, cookies [16; 17], butter biscuits [18], bread [19], cereal bars, and pancakes [20]. Therefore, grape seed flour could represent a promising alternative to wheat flour to improve the nutritional properties of bakery products [21]. Epidemiological, in vitro, and animal studies have suggested a beneficial effect of polyphenols present in grapes and grape-derived food products in metabolic syndrome biomarkers; however, human clinical trials have demonstrated controversial results [22]. Barley grain represents a great cereal resource of functional nutrients including dietary fiber, phenolic acids, folate, vitamin E, lignans, flavonoids, and phytosterols. Due to its rich composition in bioactive molecules, barley has been reported to possess cardio-protective, anti-diabetic, and antioxidant properties [23]. Dietary fiber is widely applied for the improvement of lipid profiles and its intake has been linked with a reduction in inflammation [24], insulin resistance [25], and cardiovascular disease [26]. Especially viscous fiber \(\beta\)-glucan, abundant in barley grain, has been specifically linked with the improvement of cardiovascular disease-specific biomarkers [27].