Group therapy program protocol
Other studies have demonstrated the effectiveness of psychological therapies for the treatment of depression  and obesity (weight loss)  independently, but few studies have endeavoured to treat them concurrently. To fill this gap, we developed a novel group therapy program for simultaneously treating comorbid depression and obesity within a single unified psychological intervention. The protocol incorporated a range of cognitive-behavioural, acceptance and mindfulness strategies that have been shown to be efficacious in the treatment of both depression and obesity. The resulting program consisted of 10 two-hour group sessions held weekly at the South Australian Health and Medical Research Institute (SAHMRI), co-facilitated by a psychologist and a mental health professional. Each session focused on a different topic, included reinforcement of prior learning and allocated home-based practice. Key topics covered in the program are outlined in supplemental eTable 1.
Ethical considerations and trial registration
Ethics approval was granted by the Flinders University Social and Behavioural Research Ethics Committee (SBREC) in May 2017 (Project No. 7601), and the trial was retrospectively registered with the Australian New Zealand Clinical Trials Registry (ANZCTR) (http://www.anzctr.org.au) (registration submitted 13 July 2017; registration recorded 25 July 2017; trial number ACTRN12617001079336), after the date of the first consent (6 July 2017), but before the date of the first intervention treatment session (20 July 2017). The full trial protocol is available here: (https://anzctr.org.au/Trial/Registration/TrialReview.aspx?ACTRN=12617001079336). All participants were provided with a participation information sheet and consent form prior to interview, and informed written consent was obtained for study participation. All research at SAHMRI adheres to the Australian Government National Statement on Ethical Conduct in Human Research (2007), which details sections on Scope, Methods, Recruitment, Collection and management of data and dissemination of results .
Sampling and trial design
Participants were recruited from the general population in Adelaide, South Australia by advertisement of the study on local radio, the SAHMRI website and online news media over a period of 3 months. Interested individuals were directed to a SAHMRI website to register, after which they were contacted by phone for a brief screen with one of the primary researchers. During the telephone screening, potential participants were provided with an overview of the program, key trial aims, and participation details, and they were asked whether they could commit to the 10-week program for the specified dates. Eligibility was then assessed and a face-to-face appointment to complete the initial (baseline) assessment was arranged for those meeting inclusion criteria.
Participants were assessed in four separate appointments at SAHMRI: baseline (i.e. within 2 weeks prior to the start of the group therapy program); immediate post-intervention (within 2 weeks of the program ending); 3 months post-intervention (within 2 weeks of the target date); and 12 months post-intervention (within 2 weeks of the target date). To maintain the small group size required for group therapy , two cohorts of participants completed the 10-week program at SAHMRI in a single-arm before-after pilot study design (i.e. all participants were subject to the same intervention), and the results for all participants who completed the program were analysed together. Completion of the program required participants to attend at least seven of the ten sessions (70% attendance), in order for the effectiveness of the program to be properly evaluated . Consistent with a per protocol analysis, those who did not meet this criterion (70% attendance) were excluded from analysis. The first group completed the 10-week program in July – September 2017, and the second group in January – March 2018.
Adults aged 18–65 years, with BMI ≥ 25 (i.e. overweight or obese) and scoring ≥5 on the Patient Health Questionnaire (PHQ-9 – depression screening tool)  were eligible to participate in the trial. Individuals with a major systemic or physical illness that affected weight; an uncontrolled thyroid disorder; an eating disorder diagnosed within the last twelve months; an uncontrolled psychiatric or personality disorder; a problematic use of alcohol or other substances; or intellectual impairment or other cognitive deficits that could impair progress in the group setting were excluded. Antidepressant medication use was allowed, however concurrent participation in other forms of psychological therapy for depression or obesity/weight management was not.
Demographic data (including age, sex, and cultural background) were collected via an initial survey at the first assessment appointment. Use of antidepressant medication and presence of comorbid physical health problems were also recorded.
Primary outcome measures
A range of primary outcome measures were administered. Specifically, depression severity was measured with the Hamilton Depression Scale (HAM-D), anxiety with the Hamilton Anxiety Scale (HAM-A), self-esteem with the Rosenberg Self-Esteem Scale (RSES), and body image concerns with the Body Shape Questionnaire (BSQ-34). Participant weight (kg) and height (cm) were collected and BMI was calculated (kg/m2).
Secondary outcomes measures
Health-related quality of life was assessed by the RAND-36 item Health Survey (SF-36), which measures quality of life in eight domains, including physical functioning, emotional wellbeing and general health. Physical activity (including number of days, hours or minutes of total, vigorous, moderate, and sedentary activity) was gauged with the Global Physical Activity Questionnaire (GPAQ). Nutritional intake was assessed with the Commonwealth Scientific and Industrial Research Organisation (CSIRO) Healthy Diet Score questionnaire, which provides a total overall diet quality score as well as number of daily servings of different types of food and beverages (e.g. fruits and vegetables, discretionary foods). Additional health behaviours measured included eating behaviour (for example, restrictive and emotional eating) with the Three Factor Eating Questionnaire (TFEQ-R18), alcohol consumption with the Alcohol Use Disorders Identification Test (AUDIT), and sleep quality (including various sleep components) with the Pittsburgh Sleep Quality Index (PSQI).
Additional physical measurements were also collected: specifically, waist circumference (cm), hip circumference (cm), blood pressure (systolic and diastolic mm Hg), and pulse rate (beats per minute). Waist-to-hip and waist-to-height ratios were calculated. Participants were also asked to rate their current level of mental health and physical health, as well as their readiness to change and confidence in making the changes required to improve their health.
Primary and secondary outcome measures are described in greater detail in the Supplemental materials. Score ranges and clinical interpretations are displayed in Table 2.
Evaluation of treatment acceptability
At the end of their 10-week group therapy program, participants completed a short evaluation form which asked them to rate their experience of the intervention across 22 items (e.g., each session’s quality, early experiences in the program, location, timing, group dynamics) on a 5-point scale from 1 (very poor) to 5 (very good).
Recommended minimum sample sizes for pilot studies of this nature, which are in themselves intended to determine sample sizes required to achieve appropriate statistical power and suitability for future randomised controlled trials (RCTs), is n = 12 , plus 15% for non-parametric tests  (i.e. n = 14). Our sample size exceeded that value and provided adequate power. Descriptive statistics and frequencies were generated on baseline data to describe the characteristics of the population at intake. Variables at all four time-points were inspected for outliers and distribution characteristics to check assumptions for conducting repeated measures analyses. Several variables violated assumptions of normality and outliers. Therefore, the non-parametric Friedman test was used to investigate changes in outcomes over the four time-points (baseline, post-intervention, 3-month follow-up and 12-month follow-up): p < .05 was considered significant. Follow-up pairwise comparisons were performed to determine where the significant changes occurred.