Method for modulating oxidative stress, inflammation, and impaired insulin sensitivity in a subject by using a grape seed extract, the method being useful in modulating post-prandial oxidative stress, inflammation, and impaired insulin sensitivity in patients suffering from Metabolic Syndrome (MetS). The method comprising administering a therapeutically effective amount of a grape seed extract and a pharmaceutically acceptable excipient. The grape seed extract is a polyphenolic extract comprising proanthocyanidins and anthocyanidins.