Comparison of two weight loss programs involving 16 weeks on a severely energy-restricted diet in adults with overweight or obesity: The TANGO Diet Trial (Temporary phases of Accelerated weight loss for Noticeably Greater Outcomes)

The test intervention for this research trial will be a 53-week weight loss program involving 16 weeks on a severe diet. A severe diet is defined in this research trial as a medically supervised diet that induces fast weight loss (approximately 0.5 to 2 kilograms per week), achieved by replacing all regular meals and snacks with nutritionally replete meal replacement products, such as shakes. The meal replacement products will be provided to participants by the research trial at no cost to participants. In addition to 16 weeks on the severe diet (using meal replacement products), the 53-week weight loss program will involve 6 weeks of transition from meal replacement products to regular food, and 31 weeks of weight stabilisation on regular food. After the 16 weeks on the severe diet, participants will be encouraged to adhere to a diet that follows the Australian dietary guidelines, which provide up-to-date advice about the amounts and kinds of foods to eat for health and wellbeing, based on the latest high-quality scientific evidence. To aid adherence to the Australian dietary guidelines, participants will be provided with a personal healthy eating plan from the Eat for Health Program that is associated with the Australian dietary guidelines. The personal healthy eating plan will advise each participant on how many serves to consume per day of foods from each of Five Food Groups defined in the Eat for Health Program (vegetables and legumes/beans; fruit; grain (cereal) foods, mostly wholegrain and/or high fibre cereal varieties; lean meats and poultry, fish, eggs, tofu, nuts and seeds, and legumes/beans; milk, yoghurt, cheese and/or alternatives, mostly reduced fat), and will include an allowance for unsaturated spreads and oils or discretionary choices. The personal healthy eating plan for each participant will be developed in conjunction with advice to the research team from an external Accredited Practising Dietitian, and will be based on each participant’s sex, age, height, physical activity levels and food preferences, and whether the participant aims to lose weight or remain weight-stable during the weight stabilisation phase. Participants will be encouraged to weigh themselves regularly throughout the entire 53-week weight loss program (e.g., every day), and to adjust their dietary intake, if necessary, in order to either lose weight or remain weight stable. Participants will be supported through the 53-week weight loss program with a series of weekly or fortnightly live online group support sessions (33 sessions in total over 53 weeks). Of these 33 live online group support sessions, 10 to 11 will be delivered during the 16 weeks on the severe diet, 4 to 6 will be delivered during the 6 weeks of transition to regular food, and 16 to 19 to will be delivered during the 31 weeks of weight stabilisation on regular food. The sessions will cover topics that are known to be of value for weight loss programs, such as: how to follow the severe diet; how to transition from a severe diet to a food-based diet; navigating social situations while on a severe diet or healthy eating plan; awareness of unhelpful thinking styles; getting social support; and setting progressive targets for physical activity based on gradually building up to the types and amounts of physical activity as recommended by the World Health Organisation. Outside the provision of meal replacement products and the 33 live online group support sessions, no other intervention components will be delivered as part of the weight loss program. The live online group support sessions will be facilitated by the Chief Investigator, Prof. Amanda Salis, accompanied by one or more professionals with expertise relevant to the session topic (e.g., a doctor with expertise in the treatment of high body mass index during sessions about the severe diet, an Accredited Practicing Dietitian or Registered Nutritionist during sessions about following the Australian dietary guidelines, a psychologist registered with the Psychology Board of Australia during sessions about thinking styles, a counsellor who is a member of the Australian Counselling Association during sessions about effective interpersonal communication, and an Accredited Exercise Physiologist during sessions about physical activity). The live online group support sessions will be 45 minutes in duration. The first half (20 to 25 minutes) will be dedicated to instruction about the weight loss program and will be recorded and subsequently emailed to participants, so participants can watch the session ‘on-demand’ instead of live, if desired. The remaining 20 to 25 minutes will not be recorded, and will be dedicated to a facilitated discussion about participants’ experiences of and Q+A about the weight loss program. Each participant will be in a group with of up to 20 other participants for the live online group support sessions. They will be with the same group of participants for all 33 sessions in the 53-week weight loss program. Some of the sessions will involve only participants in that participant’s own group (i.e., a total of up to 21 participants). Some of the sessions will also involve participants from other groups besides the participant’s own group. Specifically, up to 3 other groups (i.e., a total of up to 84 participants) during the severe diet and the transition to regular food, and up to 6 other groups (i.e., a total of up to 147 participants) during the weight stabilization phase. There will be a ratio of 1 facilitator for every 15 participants attending each live online group support session. Adherence to the weight loss program will be estimated in two ways: firstly, by investigating changes in weight over time; and secondly, by asking participants to bring back to the research facility the packages of meal replacement products that had been given to them in a previous visit, regardless of whether those packages are empty or not, and by counting how many of the packages have been emptied (an indicator of use). Changes in weight over time will be estimated by emailing participants once a week with a link to a secure online self-report survey and a request to weigh themselves upon rising the next day and to enter their weight and upload an image of the scales showing that weight on the display in the self-report survey.