The aim of this is study is to evaluate the acute effect of grape and pomegranate polyphenols in the modulation of markers of metabolic syndrome. Most of the previous works about polyphenols have only considered a fraction of polyphenols, i.e., extractable polyphenols. As a consequence, an important amount of dietary polyphenols, the so-called non-extractable polyphenols are ignored. In contrast, the effect of both extractable and non-extractable polyphenols will be considered in this study. Furthermore, the effect of both polyphenols as present in the food matrix and metabolites derived from microbial fermentation will be evaluated.