The Effect of Hydration Status on Glycemic Control and Appetite Regulation

The aim of this study is to investigate whether hydration status affects blood sugar control and appetite regulation. In order to do this, participants will undergo a monitoring phase whereby their weight, diet and physical activity are monitored, followed by a dehydration protocol involving fluid restriction and sitting in a heat tent. In one arm of the trial, participants will remain dehydrated for the remainder of the day (i.e. after the heat tent) by having their fluid intake restricted, and in the other arm of the trial, participants will be rehydrated by consuming the necessary amount of plain water. All participants will undergo both arms of the trial, the order of which will be chosen randomly. Several measures will be taken throughout the trial. Before participants go into the heat tent, they will provide a urine sample (for baseline hydration status as indicated by urine osmolality), a blood sample (for glucose, insulin, arginine vasopressin,/copeptin, ghrelin and serum osmolality and plasma volume), and have a peripheral quantitative computer tomography scan of their thigh to indicate muscle size. On the day proceeding the heat tent, participants will have these measures repeated, along with metabolic rate before consuming a 75 g glucose drink, followed by 15 minutely blood samples and hourly metabolic rate measures for 120 minutes (i.e. an oral glucose tolerance test; OGTT). Following this, participants will be presented with a large bowl of pasta and sauce and will be instructed to eat until satisfied (maximum 30 min). Blood samples will be taken every 10 minutes for 60 minutes following the meal. Participants also have the option to opt-in to have a muscle biopsy taken. This will be taken before and \~120 minutes after the glucose drink.