How the Body Processes Sugar After Eating, in People With Different Body Weights

The goal of this clinical trial is to learn how a high-glycaemic meal affects the way the body processes glucose in healthy adults who are either lean or have obesity. The main questions it aims to answer are: Is the polyol pathway (conversion of glucose into sorbitol and fructose) more active after a hyperglycaemic meal? Is this pathway more active in individuals with obesity compared with lean individuals? We will compare people who eat a high-glycaemic meal with those who eat a low-glycaemic meal to see whether meal type changes how glucose is metabolized in the body. Participants will drink a small amount of 14C-labelled glucose so researchers can trace how the body uses glucose, spend one long study day (about 12 hours in the lab) plus short morning visits on days 2 to 4, and undergo repeated measurements, including blood sampling, breath sampling, indirect calorimetry, and complete urine and stool collection for 72 hours. This information will help us understand how glucose is processed in the body and whether people with obesity handle glucose differently than lean individuals.