Re calibrating the body clock: the impact of restricting the daily feeding window on skeletal muscle health and circadian rhythms in overweight/obese males.

Restricted feeding: daily feeding window limited to 8 h for 5 days. Participants will receive a participant information letter outlining study procedures and a handbook to log physical activity levels and sleep during the intervention. On trial days, study researchers will use hard copy run sheets to adhere to the study protocol. New staff members will undergo formal training by study coordinators for data collection purposes and receive a standard operating procedure manual.Experimental conditions will take place at the Exercise Science and Nursing facilities within the Daniel Mannix Building at Australian Catholic University. Visit 1: Total time ~ 1 hour 30 min. This visit on any weekday morning that suits. It will occur between 5-10 days before the start of the intervention period (Visit 2). Anthropometric measurements: Height will be measured using a wall mounted stadiometer. Weight will be measured using digital scales. Hip, waist and neck circumference will be measured with a metal tape measure. All measures will be taken in duplicate.Resting Metabolic Rate (RMR): Participants will be required to 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 are required to lay supine on the scanning bed for the duration of the 15 minut 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 should be worn 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 ARPANSA. Blood pressure: blood pressure (BP) will be measured via an automated blood pressure 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: At this visit, participants will be given a three day diet record to complete prior to both experimental conditions. Participants will be asked to record all food and fluid consumed over a three-day period prior to both experimental conditions. Prior to the second experimental condition, participants will be asked to replicate, as close as possible, the dietary intake consumed in the lead up to the first experimental condition whilst still recording dietary intake during this time. Visit 2 and 4 (Day 0): Total time ~ 1 hour 30 min. This will always be on a Saturday morning. Visit 2 will occur 5-10 days following visit 1. Visit 4 will take place after the first intervention arm and the 14 day washout period. Continuous blood glucose monitoring (CGM): participants will be required to wear the minimally invasive Medtronic iPro2 blood glucose monitoring system for duration of both experimental conditions. The monitor is the size of a 50 cent piece and inserted rather painlessly into the subcutaneous tissue of the lower back. The iPro2 will be worn for the pre-trial days (Day 1-4), and then throughout the 24 h laboratory visit (Day 5-6). 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 tricep muscle, to be worn continuously throughout both experimental conditions. Participants will be instructed to replicate the same ‘activity’ patterns during their second treatment. Participants will be instructed to maintain their usual sleep pattern and avoid all activities impacting circadian rhythm (e.g. late night television). Visit 3 and 5 (Day 5-6 of intervention): Total time ~24 h. Occur following Day 1-4 of following the diet intervention. Throughout the 24 h stay in the laboratory, muscle biopsy and BP measurements will take place every 4 hours (12 in total). Blood samples will be taken hourly between 0700 and 2300 (17 in total) and two hourly from 2300 until 0700 (4 in total). Blood sampling: an in-dwelling venous catheter will be inserted and 252 mL of blood in total will be collected across the two trials. Four-hourly blood samples will be collected. All samples will be centrifuged immediately, the plasma or serum removed and frozen immediately (-80 degrees C) for later analysis. Muscle biopsy: The first muscle biopsy will be taken at 0700 h regardless of experimental condition and immediately frozen (-80 degrees C) for subsequent analysis. The muscle biopsy will be taken by Dr Andrew Garnham (20 years experience). Muscle biopsy samples will be taken every 4 hours after 0700 h with the last at 0300 h. Six muscle biopsies will be obtained for each experimental condition. Blood pressure: Measurement procedure as described in Visit One. These will take place every 4 hours as per the same time schedule as the muscle biopsies. Dietary intervention: During Days 1 to 4, participants will consume provided meals within an 8 h window (1000 h to 1800 h; RESTRICTED condition). During Day 5 participants will attend the laboratory for a 24 h period while continuing to eat provided meals across the same 8 h time window. The diet provided will be a high-fat, low carbohydrate diet containing 50% fat, 30% carbohydrate, 20% protein. Total daily kilojoule intake will be determined from the RMR measurement in Visit One and using a physical activity factor of 1.4. The same diet will be provided for both conditions, yet, the timing of intake will differ. An Accredited Practising Dietitian (Dr Brooke Devlin) will design and implement all diets. Participants will be provided with a comprehensive food checklist for the 5 day intervention period and will be asked to tick off foods once consumed to monitor adherence. Additionally, they will be asked to note down the time the meals are consumed. Verbal confirmation will also take place upon arrival to the 24 h lab stay. There will be a 14 day washout period between trial. Following both trials, participants will take part in a semi-structured qualitative interview to investigate their perspectives on the timing of meals in each condition and whether or not they believe they could apply the different timing of meals to their daily routine. This will be completed once only (15 minutes).