 Before and after the supplementation period, we perform a hyperinsulinemic-euglycemic clamp with a glucose-tracer infusion to assess hepatic and systemic insulin sensitivity. Simultaneously, substrate oxidation is measured throughout the clamp by indirect calorimetry. Furthermore, we perform a high-fat mixed meal test, in which we collect blood and measure substrate oxidation during fasted and postprandial conditions. During the meal tests, extra plasma is collected at the start t-30 and the end t240, of which the supernatant is stored in light-protected tubes EGCG is mixed 1:1 with an EGCG buffer for analyzing polyphenol concentrations in the blood. 