Fast Track to Health. The effect of intermittent energy restriction on weight loss and well-being among young people above a healthy weight. (Formerly known as Fast Track to Health. The effect of a modified alternate day fasting dietary pattern on weight loss and well-being among young people above a healthy weight).

The Fast Track to Health study is a multi-centre randomised controlled trial weight-loss intervention. The aim of this study is to determine if an intermittent energy restricted dietary pattern results in significant weight loss and a lower body mass index (BMI) z-score after 52 weeks (12 months) of intervention in adolescents with obesity compared to a standard care, reduced calorie dietary pattern. Trained dietitians will be primary contacts for participants. Participants will see the dietitian approximately 10-13 times during the study period. Aside from dietitians, participants will have contact with health professionals including paediatricians and practice nurses during the study. Participants may also be assessed by a clinical psychologist. Most appointments will be 30-45 minutes, however 4 appointments at baseline and weeks 4, 16 and 52 will be longer taking about 3-3.5 hours to allow for collection of outcome measures. Study sites are: The Children's Hospital at Westmead (Sydney), or at the Be Active Sleep Eat (BASE) facility at Monash University (Melbourne) or Monash Children's Hospital (Melbourne). There are three phases to this study: Phase 1 (Week 0-4) All participants will complete a Very Low Energy Diet (VLED) using meal replacements for up to 4 weeks. The diet prescribed during Phase 1 will provide approximately 800kcal/day, consisting of less than 40% of energy from carbohydrate (about 50g/day), 40-55% of energy as protein and less than 20% of energy as fat. Meal replacements will be provided by the study team during phase 1. Blood ketones will be measured weekly via a finger prick meter during phase 1 to evaluate adherence to the VLED protocol. Early transition to the prescribed diet can occur based on dietetic clinical judgement. Participants will see the dietitian weekly during phase 1. Phase 2: (Week 4-16) Participants will be randomised to receive one of the two dietary patterns: Intermittent Energy Restriction (IER) or a reduced calorie dietary pattern. The dietitian will provide detailed meal plans and information for both patterns. Participants will choose and pay for their own food for the remainder of the intervention. Participants will have an option to transition off the VLED replacements during weeks 4-6 in which meal replacements will be provided free of charge. Dietitian visits will be scheduled at weeks 6, 9 and 12. A 'coaching' model will be used during consultations, providing a theoretical basis for psychological variables important in achieving dietary compliance, lifestyle change and weight loss. Additional support via text message, phone or email (depending on participant preference) will also be provided at weeks 8, 11 and 14. Duration of support contacts will be approximately 10-15 minutes. All participants will be given a commercial multivitamin (containing essential fatty acids) to improve micronutrient intake. Participants will be given a sealed bottle of Cenovis Once Daily 50+ Multivitamin and will be instructed to take 1 capsule daily from week 5 to 52 of the study. Each capsule contains fish oil, b-carotene, vitamins A, B1, B2, B3, B5, B6, B7, B9, B12, C, D, E and K, boric acid, calcium carbonate, cupric sulfate, chromium picolinate, magnesium oxide, ferrous fumarate, manganese sulfate monohydrate, selenomethionine, zinc oxide and potassium iodide, and citrus bioflavonoids and linseed oil. Dietitians will calculate the visit that participants should require a new bottle and record when they need a new bottle as a measure of compliance. Intermittent Energy Restriction (IER) This involves a very low energy diet for 3 non-consecutive days per week (approximately 600-700 calories/day) and a standard healthy diet for 4 days per week. No energy restriction will be used on feeding days, but participants will be given healthy eating guidelines based on the Australian Dietary Guidelines. Discretionary foods will be limited to one standard serve per week. Participants will also have one 'meal off' per week included in their meal plan to accommodate occasional eating out or social gatherings. Standard hypocaloric diet This involves a higher fibre (>30g per day), moderate carbohydrate (40-50%) and moderate protein (20-25%) dietary pattern. The diet will have prescriptive energy levels based on age: 6000-7000kJ (13-14 years), or 7000-8000kJ (15 - 17 years). Phase 3: (Week 16-52) Participants in both the experimental arm and active control arm will continue their prescribed intervention during this phase. The dietitian will review intake and weight loss at each visit, modify goals as necessary and encourage adherence to the intervention. Dietitian visits will be scheduled at weeks 20, 26 and 36. Additional support via phone, email or text message (depending on participant preference) will be offered at week 18, 24, 28, 42 and 48. Duration of support contacts will be approximately 10-15 minutes. All participants will receive standard advice for physical activity, screen and sleep time as per the Australian Physical Activity & Sedentary Behaviour Guidelines for Young People. 24 month follow up At the final study appointment (week 52), participants and their parent/guardian will be asked if they agree to be contacted by the study team in 12 months (i.e. 24 months post-baseline). This is not an essential component of the study. A consent form will be signed before contact is made. Participants who consent to be contacted 24-months post-baseline will be invited to attend a single follow-up appointment.