Defining the Human Insulin Resistance Molecular Network; SIGNATURE

The goal of this intervention study is to learn more about what causes insulin resistance in otherwise healthy adults, and how short-term changes in physical activity or diet may influence it. The study includes healthy male and female participants aged 25 to 55 years, who meet specific health criteria. The main questions it aims to answer are: Does the cause of insulin resistance vary between individuals due to their genes and lifestyle? Can the investigators identify different types (sub-phenotypes) of insulin resistance at the molecular level? Researchers will compare groups who either reduce their physical activity for 14 days or consume a high-fat diet for 3 days, to see how these changes affect insulin sensitivity and related biological markers. Participants will: * Complete a health screening and be assessed for eligibility * Undergo baseline testing to measure insulin sensitivity, physical activity, diet, and metabolic health * Be randomly assigned to one of two short-term interventions (14 days of reduced physical activity, or 3 days of a high-fat, high-calorie diet) * Repeat selected tests after the intervention to assess changes This study will help researchers better understand how lifestyle and biology interact in the development of insulin resistance, even in people who are otherwise healthy.