Vitis Intervention Trial in Substrate Metabolism

Obesity is associated with reduced metabolic flexibility (MetFlex), the capacity to shift between carbohydrate and lipid oxidation in response to nutrient availability. Grape polyphenols (resveratrol, catechins, quercetin, epicatechin) enhance fat oxidation and mitochondrial function in laboratory and animal studies, but whole grapes, rather than purified extracts, have not been tested for acute effects on MetFlex measured directly by whole-room calorimetry paired with mitochondrial function. This study integrates whole-room indirect calorimetry with high-resolution respirometry in peripheral blood mononuclear cells (PBMCs) to determine whether whole grape polyphenols shift the postprandial respiratory exchange ratio (RER) response to a high-fat meal and alter mitochondrial respiration, and whether responses differ by adiposity phenotype (lean vs. overweight/obesity).

Inclusion Criteria: * Men and women aged 25-60 years * BMI 18-24.9 kg/m² (lean phenotype, n=10) or BMI 25-40 kg/m² (overweight/obesity phenotype, n=10) * Low habitual grape consumption * Weight stable (no change \>5% in prior 6 months) and not actively attempting weight change * White blood cell count within normal limits Exclusion Criteria: * Current smoking; drug or alcohol abuse * Claustrophobia or psychiatric conditions that would make a 40-hour confined stay especially distressing or harmful * Weight instability, recent/active weight-loss attempts, or structured exercise initiation during the study * Hormone replacement therapy or medications known to affect metabolism * Pregnant or breastfeeding * Current or prior bulimia nervosa, binge eating disorder, or anorexia nervosa * Grape allergy, or food allergies/intolerances precluding use of the metabolic kitchen * Any condition that, in the PI's opinion, would make participation unsafe or could interfere with conduct/interpretation of the study