Nocturnal blood glucose responses to potato-based mixed evening meals

The blood glucose response of all participants who consume four mixed meals including a potato element (boiled, baked or boiled then cooled) or basmati rice (control) on four occasions separated by a minimum of 7 days will be measured. Overview of design: Twenty four participants with type 2 diabetes mellitus (T2DM), male and female, body mass index (BMI) 22 – 40 kg/m2 and aged 35 – 75 years old, will be included in a randomised cross-over study. All participants will complete all four conditions in random order with a minimum 7-day wash-out period between trials. Four evening meal conditions will be tested including dinner of meat and vegetables with either BOILED, BAKED, BOILED THEN COOLED potato or a CONTROL of basmati rice. All meals will be matched for energy and macronutrient composition. Daily diet composition will be 50% carbohydrate, 30% fat and 20% protein. Each meal will be the same composition as the overall daily diet composition. Energy distribution over the day will be 25% of total energy intake (TEI) at breakfast, 30% TEI at lunch and 45% TEI at dinner. Potato and rice will make up the carbohydrate content of the evening meal. Materials: Participants will receive a Participant Information Letter outlining study procedures and a handbook to log physical activity and sleep during the intervention. Checklists for standardised meals to be consumed, space to record dietary intake and an outline of scheduled laboratory visits will be included in a handbook provided. Procedures: Experimental conditions will take place within the Daniel Mannix Building at Australian Catholic University. Participants will attend the laboratory on a minimum of 18 occasions as outlined below: Visit 1: Forms. Study procedures explained prior to obtaining written consent. Visit 2: Baseline measurements. Resting metabolic rate (RMR), Dual-Energy X-Ray Absorptiometry (DXA), blood pressure and anthropometric measurements. Visits 3, 6, 9 & 12 (Day - 3): Monitors and provision of standardised meals. A continuous glucose monitor (CGM) and three activity monitors will be inserted/put on. Participants will collect their standardised meals for consumption the day before the trial day (to be consumed on Day 0). Visits 4, 7, 10 & 13 (Day 1): Trial days. Participant will attend the laboratory at 7am. A fasted blood sample will be collected at this time and breakfast and lunch will be provided for participants to consume in their “free living” environment that day. Participants will return to the lab that evening to have a cannula inserted to collect blood samples following consumption of one of the four dinner meals. These four visits require participants to attend in the morning (for the fasted blood sample) and then they are free to leave but will be required to return for the evening. Therefore, there are four additional occasions participants will need to attend the lab but are part of the same Trial day (i.e. am and pm visits). Visits 5, 8, 11 & 14 (Day 2): Blood sample and monitor removal. Participants will return to the lab for collection of a fasted blood sample and removal of monitors. Following a minimum 7 day “washout period”, participants will re-attend the lab and repeat visits 3 – 5 until all four conditions are completed. Description of study procedures: RMR: Participants will lie down in a quiet, dim-lit room for 25 min where RMR will be measured using an automated gas analyser. A hood (clear) will be placed over the participants head and connected to the gas analyser. The 25 minutes includes a 10 minute rest period, followed by a 15 minute period of data collection. DXA: Participants will undergo a whole body DXA scan. Participants will lay supine on the scanning bed for the duration of the 15 minute scan. There will be one to two scans depending on the body shape of the participant. The machine uses small doses (<1% of the yearly radiation dose) of radiation to estimate tissue density. The total effective dose of radiation has been calculated for this machine and the scans for this study by a Medical Physicist. This test requires the participant be fasted with no food, fluid or exercise/activity prior to the test. Light clothing with no metal items (i.e. zips, domes, clips, underwire etc.) should be worn (gowns are available if need be) and all jewellery must be removed. All measures will be taken by trained researchers who hold radiation licences with Victorian Government and comply to the Code of Practice set out by the Australian Radiation Protection and Nuclear Safety Agency. Blood pressure: blood pressure (BP) will be measured via an automated BP machine. Three measures will be taken, a minimum of 1 minute apart. Each measure is approximately 3 minutes in duration. The participant will have a cuff applied to the upper portion of the arm. This will inflate and tighten around the arm and then slowly release. Three-day dietary record: Participants will asked to record their habitual dietary intake on the three days preceding the first experimental trial. They will be asked to mimic this as closely as possible prior to the three subsequent trials. Continuous blood glucose monitoring (CGM): Participants will be required to wear the minimally invasive Medtronic iPro2 blood glucose monitoring system for the four day period prior to all four trials, each trial day and the following morning. The monitor is the size of a 50 cent piece and the associated sensor inserted rather painlessly into the subcutaneous tissue of the lower back. Physical activity and sleep monitors: To assess physical activity and sleep, participants will be fitted with an inclinometer (ActivPAL3TM) worn on the thigh, an ActiGraph accelerometer worn around the waist, and a SenseWear armband worn on the triceps muscle, to be worn for the four day period prior to all four trials, each trial day and the following morning. Blood sampling: Eight samples will be collected during each of the four trial periods (32 samples in total). The total volume collected across the minimum 8 week period will be 192 mL.