Shifting the Risk Study (Investigating meal timing and heart health in shift workers)

PROCEDURES Participants will be randomised to begin with the Intervention period or the Control period. There will be a minimum of two week washout between the two periods. Intervention period (manipulation of meal times) Participants will be asked to avoid food intake for a five hour period during the night, for a continuous four week period (minimum 28 days). They will receive a face-to-face individual meeting with a dietitian, who will provide them with a tailored eating plan, to redistribute the timing of food intake. During the four week Intervention period, participants will also be asked to: - Complete one 24-hour food recall each week (four in total). - Wear a Sensewear activity monitor for 5 days. The Sensewear activity monitors are used to collect physical activity information. During the study period, participants will also be asked to collect urine for a continuous 48-hour period (maximum of two occasions). This is used to analyse the concentration of aMT6s, which is the primary urinary metabolite of melatonin. In order to measure metabolic outcomes, participants will be asked to partake in acute meal challenges: once at baseline and once after the Intervention period. Each acute meal challenge will run for approximately 7 hours (~8am – 2:30pm). After a 10-hour fast, participants will arrive at the Be Active Sleep and Eat (BASE) facility at 8am. Anthropometric (weight, waist circumference) and body composition measures will be taken. A trained nurse or phlebotomist will then insert a cannula in the participant’s forearm and a baseline blood sample will be taken. Participants will be provided with a high fat breakfast meal (~45% energy from fat), to be consumed within 15 minutes. Blood samples will be taken for a total of 6 hours post-meal (timing begins at commencement of meal intake): at 15, 30, 45, 60, 90, 120 minutes and then hourly for the next 4 hours. The maximum amount of blood that will be collected during this 6-hour period is 120ml. Participants will be permitted water (but no other food or drinks) and are to remain sedentary during this period. Participants will also be asked to complete surveys regarding their shift schedule, sleep, exercise habits and general well-being during this period. WHO WILL DELIVER THE INTERVENTION: Participants’ progress through the entire study will be monitored by two PhD students from the Department of Nutrition, Dietetics and Food of Monash University, Australia. The dietetic consult will be performed by an Accredited Practising Dietitian. Trained nurses or phlebotomists will perform cannulation and blood draws during the acute meal challenges. MODE OF DELIVERY The intervention of the study is avoiding food intake at night for a specified period. Participants will receive an initial face-to-face individual meeting with a dietitian, who will help them reorganise their usual meal pattern to avoid food intake between the specified hours. As the participants will be asked to maintain the types and amount of food they usually eat, changing only the timing of food intake, regular follow-up with the dietitian will not be necessary. However, they are encouraged to contact the dietitian or other research team members by phone or email if they have difficulties maintaining this intervention. LOCATION The participants will be free-living. The acute meal challenges will be conducted in the Be Active Sleep and Eat (BASE) Research Facility at Monash University (Notting Hill, Victoria, Australia). DURATION AND TIME FRAME The entire study will be approximately 13 weeks in duration. Participants will be in the Intervention period for a continuous 4 weeks (28 days minimum). The acute meal challenges will be conducted once at baseline and once after the Intervention period. Each of acute meal challenges will be approximately 7 hours in duration. Participants will meet with the dietitian during the acute meal challenge prior to the commencement of Intervention period, this will take 30 minutes to an hour. TAILORING Individually tailored meal plans will be provided, in regards to the redistribution of food intake to other times of the day to avoid the specified period during the night. Participants’ food preferences and usual meal times will vary; dietary advice will be based on these. MAINTAINING ADHERENCE During the Intervention Period, participants will be sent automated text messages on every night shift, to remind them not to eat at night. 24-hour food recalls will be completed once a week during the Intervention period to help monitor compliance. Participants will be contacted via phone on their first day off after a continuous row of night shifts and be asked to recall their intake of the day prior.