Effects of Exercise and Energy Balance on 24-hour Blood Glucose Control

Overview

The study team will assess "free-living" 24h glucose control using continuous glucose monitors (CGM) over an 88h period on two separate occasions. Importantly, standardized meals will be provided and will be consumed at specific times each day of the CGM measurement period. These meals will be identical on day 1 and day 3 of measurement. Each subject will complete two CGM periods, which will be identical except for the calorie and macronutrient content of the post-exercise dinner. In addition, during trial 1, two CGM's will be worn, while only 1 CGM will be worn on trial 2.

Subjects will be instructed to exercise exactly 2 days before each experimental trial period, and then abstain from exercise other than the exercise session on Day 2 of the trial period until after the trial period is complete. Subjects will arrive to the Substrate Metabolism Laboratory at approximately 4pm on Day 0 of each trial. For trial 1, two CGM devices will be placed on either side of the abdomen, near the belly button. For trial 2, only one CGM device will be placed on one side of the abdomen. On Day 1 of both trials, participants will go about their normal daily activities (other than planned exercise) while eating provided meals at designated time points. This day will serve as the non-exercise control day. On Day 2, subjects will return to the laboratory to exercise on the bike for \~1h at a moderate exercise intensity (approximately 65% of their measured VO2peak) to expend 350 kilocalories. During trial 1 only, subjects will use the mouthpiece and nose clip (which will allow all of their expired air to pass through the metabolic cart for analysis of oxygen consumption and carbon dioxide production) for \~5 min at the beginning, middle and toward the end of exercise to verify they are exercising at 65% of VO2peak. This will also allow the study team to accurately measure energy expenditure (kcal) during exercise. On trial 2, subjects will perform the exact same exercise protocol, but the mouthpiece and nose clip will not be required. One hour after the exercise session, participants will eat their standardized dinner. Importantly, the caloric content of this meal will differ between the two trials (+/- 350kcal), and this will be the only difference between the two study trial periods. On Day 3, participants will go about their normal daily activities (other than planned exercise) while eating the provided meals at designated time points. This day will serve as the post-exercise day. On Day 4, participants will return to the laboratory at approximately 8am for removal of the CGM device(s).