## 2 Materials and Methods
### Experimental Treatments  
Dried olive leaves were obtained from AS Dolon, Kalamata, Greece. Upon receipt, the leaves were thoroughly rinsed, dried, and then dehydrated in an oven at 70 \({}^{\circ}\)C for 150 min. The selected drying temperature and duration were based on preliminary in vitro experiments conducted by our research team to optimize the retention of phenolic compounds and antioxidant activity in the olive leaf samples. After dehydration, the leaves were ground into a fine, homogeneous powder (from a 200 g batch) suitable for incorporation into the tea and biscuit products. A detailed chemical characterization of the olive leaf powder, including its phenolic composition and antioxidant properties, has been conducted in parallel in our laboratory. The results of these in vitro analyses are currently under preparation and will be presented in a separate forthcoming publication.  
Prior to the clinical intervention, a separate sensory evaluation study was conducted to determine the most acceptable concentration of olive leaf tea. Initially, four different concentrations of olive leaf powder were pilot-tested internally by the research team (0.25%, 0.5%, 0.75%, 1%, and 2% \(w/v\)). Based on preliminary observations and practical considerations, the two most promising concentrations--0.5% and 1% \(w/v\) (corresponding to 1.25 and 2.5 g of olive leaf powder per 250 mL of water, respectively)--were selected for formal sensory testing. The selection of these two concentrations was based on multiple factors, including sensory acceptability, anticipated compliance with repeated intake, and the need to ensure a meaningful intake of bioactive compounds. Very low concentrationswere excluded from the sensory trial to avoid compromising the expected polyphenic and antioxidant potency. In addition, previously published studies using olive leaf infusions were reviewed to guide dose selection within a physiologically relevant and safe range. The sensory study involved an independent group of 34 untrained volunteers (aged 18-65 years) and followed a single-blind, within-subject crossover design. Each participant evaluated both selected tea samples under controlled conditions and rated them. The teas were brewed with boiling water, refrigerated overnight, and served chilled at 10 \(\pm\) 2 \({}^{\circ}\)C. Sensory attributes, including color, aroma, taste, aftertaste, and overall acceptance, were rated using a 9-point hedonic scale (1 = dislike extremely, 9 = like extremely). Additionally, participants indicated their preferred sample. Based on participants' preferences and sensory scores, the 0.5% (\(w/v\)) concentration was selected for the clinical trial.  
Olive leaf tea for the clinical trial was prepared at the concentration determined from the sensory evaluation by adding 250 mL of boiling water to 1.25 g of olive leaf powder and letting it infuse for 5 min. The tea was then refrigerated overnight to be served chilled. In parallel, the biscuits were produced by incorporating 1.25 g of olive leaf powder into the dough intended for each participant's serving.  
Both test products were provided as part of a standardized, high-fat and carbohydrates meal, specifically designed to assess the postprandial metabolic effects. Each participant consumed a mixed meal consisting of 140 g of dough, providing 683 kcal, 75 g of carbohydrates, 7 g of protein, 39 g of fat, and 1.92 g of dietary fiber.