Health effects of treating sleep apnoea with Continuous Positive Airway Pressure (CPAP) during weight loss in people with pre-diabetes, sleep apnoea and obesity.

Intervention: CPAP with a Weight Loss Program CPAP: Participants assigned to the intervention group will be provided with a CPAP machine that with automatically titrate a therapeutic pressure. Prior to commencing CPAP the participants will receive CPAP education and undergo a mask fitting with a CPAP therapist. Participants will be issued with a CPAP and mask to use all night during sleep at home for the three months of the trial. Participants will have 2 pre-arranged consultations (face-to-face or by telephone) for approximately 20 minutes at 2 weeks and 1 month to assist with the initial use of CPAP. Participants can also request additional consultations (as required) with the CPAP therapist to assist with ongoing use of the CPAP device. Weight Loss and Maintenance Program: Participants in the intervention group will also receive support with a Weight Loss and Maintenance Program administered by the study dietitian. The patients will receive a lifestyle consultation by phone call from the dietitian at 1 and 2 week time points. Participants will also attend the Woolcock Institute to participate in individual face-to-face lifestyle consultations conducted by the dietitian running for 1-1.5 hours at 1 and 2 months. Participants will also be invited to participate in optional weight maintenance support from the three month time point until the 12 month time point. The weight maintenance support appointments will involve a phone call at 5 and 7 months and a face-to-face consultation at 9 and 12 months. Participants will be asked to document diet, exercise, and sleep habits daily at periods during the trial. They will also be asked to complete a 4-day food diary at 0, 5 and 12 months. 24-hr food recall will also be undertaken at 0 weeks, then at 1, 2, 3, 7 and 9 months to confirm dietary compliance. Dietary program during the weight maintenance phase: Total daily energy intakes will be prescribed according to participants’ energy requirements, as estimated using the Harris-Benedict equation with an appropriate activity factor (it is suggested all activity be underestimated to ensure a conservative approach) and 2000kJ/500calorie /day energy deficit to encourage weight loss. Four levels of daily energy will be used in this study (5,7, 9 or 11 MJ/day) and participants will be prescribed an energy level which is closest to their energy intakes as calculated above. Desired macronutrient distribution will comprise 45% daily energy intake from carbohydrate, 25% from protein, 30% from fat and <1% from alcohol. The diet will aim to be as low in GI as practical and achieved by replacing higher GI carbohydrates with lower GI carbohydrates. Exercise program during weight loss and weight maintenance phases: Participants will be provided a safe, tailored exercise prescription with consideration of existing comorbidities or musculoskeletal limitations. The frequency, intensity and volume of exercise will be tailored according to the following progressive targets based on the Australian Physical Activity Guidelines for the general population and the American College of Sports Medicine (ACSM) guidelines for clinically significant weight loss: 1. Commencing with: at least 150 minutes per week of moderate intensity activity, i.e. 30 minutes on most days (Australian Physical Activity Guidelines for the general population) 2. Increasing to: at least 250 minutes per week of moderate intensity cardio exercise, i.e. 45-60 minutes most days (ACSM guidelines for clinically significant weight loss) 3. Plus: at least 1 session per week of ~20-45 minutes strength training 4. Increasing to: 2 times per week. (48-72 hours recovery between strength training sessions) 5. Plus: flexibility Lifestyle counselling: Individual dietary counselling is necessary to identify current dietary patterns, recommend specific changes, and identify barriers and target behavioural change strategies to the individual successfully. Sessions will consist of a combination of diet and exercise reinforcement and will provide the opportunity to progress exercise prescriptions as well as monitor dietary compliance. Health coaching techniques will support behaviour change and techniques are based on the Health Coaching Australia techniques in which the study clinicians are trained. Written materials: Participants will be provided with written educational materials that outline their dietary and exercise prescription including the food amounts that constitute one serving and the carbohydrate options and safe/sustainable dietary and exercise recommendations to support weight loss and maintenance.