Altering the timing of breakfast and exercise to modify post-meal glucose concentrations: The Breakfast and Exercise Timing (BET) Study

Participants will be randomly allocated into the order to complete each of the different timings of breakfast (conditions: Early at 7:00 am, Mid at 09:30 am and Delayed at 12:00 pm) and will be asked to follow the prescribed breakfast time and exercise. In a free-living environment, we will provide the participants with Freestyle Libre Pro iQ continuous glucose monitors (CGM Pro iQ), physical activity monitors (ActivPAL), and a wrist-worn sleep monitors (Actiwatch Spectrum), participants will consume breakfast for 8 days at one of the three prescribed times, and in the final 4 days of each 8 days will be asked to complete 20 min brisk walk within 30 min to 1 h after starting breakfast. After 6 day washout periods (allowing for a new sensor), the second and third conditions will be conducted. Prior to commencing the intervention conditions, participants will complete a 6-day baseline period in which they will be free-living, recording their food diary, food photos and wearing the CGM Pro iQ, ActivPAL, and Actiwatch Spectrum. Participants will attend the laboratory on a minimum of 5 occasions with a total of 4 hours across the visits. In the 3-hour pre-study visit (V0) we will provide the participant with a handbook, specifically designed for this study, with the monitor information (i.e., removing the activity monitors, retaining the glucose sensor if it detaches) and detailed recording sections for each day of the intervention. We will also provide participants with a calendar for the study conditions according to each randomisation and we will explain the overview of the study where breakfast and exercise advice will be provided. We will also explain to participants how to complete dietary recordings (e.g. taking images at each eating occasion). At the pre-study visit, we will test HbA1c to assure eligibility and type 2 diabetes diagnosis, we will do a mixed meal tolerance test (MMTT), and a Dual-energy-X-ray absorptiometry scan for body composition. Each of visits 1-4 will be ~20 minutes, and we will collect the participants food diary, provide participants with breakfast for the next condition, and fit new glucose and activity/sleep monitors. We will also remind them about the specifications for their next condition. We will individualize the breakfast for each participant according to their habitual breakfast, matching the 25% of their energy requirements according to the Schofield equation with a 1.3 physical activity factor.