The impact of adult behavioural weight management interventions on mental health: A systematic review and meta‐analysis

There is good evidence that behavioural weight management interventions improve physical health; however, the impact on mental health remains unclear. We evaluated the impact of behavioural weight management interventions on mental health‐related outcomes in adults with overweight or obesity at intervention‐end and 12 months from baseline. Eligible studies were randomized controlled trials (RCTs) or cluster RCTs of adult behavioural weight loss interventions reporting affect, anxiety, binge eating, body image, depression, emotional eating, quality of life, self‐esteem and stress. We searched seven databases from inception to 7 May 2019 and included 43 articles reporting 42 RCTs. Eighteen studies were deemed to be at high risk of bias. We conducted random‐effects meta‐analyses, stratified analyses and meta‐regression using Stata. Interventions generated greater improvements than comparators for depression, mental health‐related quality of life and self‐efficacy at intervention‐end and 12 months from baseline. There was no difference between groups for anxiety, overall quality of life, self‐esteem or stress at intervention‐end. There was insufficient evidence to assess the impact on anxiety, binge eating, body image, emotional eating, affect, life satisfaction, self‐esteem or stress at intervention‐end and/or 12 months from baseline. Although evidence suggests that interventions benefit some aspects of mental health, high‐quality, transparently reported RCTs measuring a range of mental health outcomes over longer durations are required to strengthen the evidence base.


| INTRODUCTION
Overweight and obesity are associated with increased risk of conditions such as cardiovascular disease, type 2 diabetes, stroke, osteoarthritis and some cancers, as well as greater all-cause mortality. [1][2][3][4][5][6] Additionally, obesity is related to an increased risk of poor mental health including mood disorders, anxiety and psychiatric disorders. 7,8 There is good evidence that behavioural weight management interventions can improve physical health in people with overweight and obesity. 9,10 However, the evidence for their impact on mental health is less clear.
Some studies have reported mental health improvements with weight loss. [11][12][13][14][15] However, qualitative evidence suggests that there is inadequate support for mental health and emotional well-being in weight management interventions. 16 Some studies also report concerns that a focus on dietary restriction may influence disordered eating and increase psychological distress. [17][18][19][20] Greater understanding of the impact of weight management intervention on mental health is necessary to inform the development of interventions to support both mental and physical health concurrently, optimizing care and minimizing the risk of harm.
Previous systematic reviews have aimed to synthesize evidence for the impact of behavioural weight management interventions on various aspects of mental health; however, findings have been limited and conflicting. 17,[21][22][23][24][25][26] For example, Warkentin et al. 23 concluded that weight loss may be associated with improved physical health but not mental health, Fabricatore et al. 25 reported statistically significant reductions in depressive symptoms following behavioural weight loss interventions, and Lasikiewicz et al. 24 concluded that weight management interventions are associated with improvements in multiple mental health outcomes including self-esteem, body image, quality of life and depressive symptoms.
Previous reviews have also highlighted the breadth of mental health outcomes that could be affected by attending a weight management intervention; however, the majority of reviews have focused on a limited number of outcomes. 17,[21][22][23][24][25][26] It is important to generate a comprehensive understanding of the impact of weight management programmes on mental health as the benefits of improvements in one domain may be undermined by negative impacts on another. Previous reviews have also excluded participants with any concurrent physical or mental diagnosis to constrain the search or to exclude illnesses associated with unintentional weight changes (e.g., chronic obstructive pulmonary disease or cancer). 17,27 Overweight and obesity are associated with increased risk of a wide range of comorbidities 28 ; therefore, the exclusion of these participants limits the representativeness of findings.
The limitations of previous reviews and inconsistent findings make it difficult to draw clear, reliable conclusions on the impact of behavioural weight management interventions on mental health. To our knowledge, there is no up-to-date, comprehensive review investigating the effect of weight management interventions on a broad range of mental health outcomes in a representative sample of adults with overweight or obesity, or investigating whether particular intervention or study characteristics are more supportive of mental health. Therefore, we aimed to: 1. Quantify the effect of behavioural weight management interventions on mental health in adults with overweight and obesity compared with inactive/minimal intervention or 'usual care' comparator groups.
2. Quantify whether particular study, intervention or participant characteristics influence the effect of interventions on mental health.

This review adheres to Preferred Reporting Items for Systematic
Reviews and Meta-Analysis (PRISMA) reporting. 29  Outcomes reported at intervention-end and at 12 months from baseline were extracted, regardless of intervention duration. We chose these a priori defined outcomes as they were deemed to be the most relevant, were most frequently reported in previous relevant literature, represented the most prevalent mental health conditions and provided the most comprehensive insight to date into mental health impacts of behavioural weight management interventions.
5. Study designs: Individual or cluster randomized controlled trials (RCTs). Non-English language publications were excluded.

| Study selection
Two-stage screening was completed in duplicate, with a third reviewer resolving discrepancies. 30 We contacted study authors (n = 2) to resolve any uncertainties about eligibility. Where studies were reported in more than one publication, all articles that met eligibility criteria were included and combined to make best use of the data available.

| Data collection
Data extraction was completed by one investigator with full checking by one further investigator. Discrepancies were resolved through discussion, with use of a third investigator where necessary. We contacted study authors (n = 26) to request missing data. If there was no response, authors were sent two email reminders. Authors were given a minimum of 2 months to respond. Authors of six studies did not respond, five responded that data was unavailable, and 15 responded with the data requested.

| RoB in individual studies
Risk of bias (RoB) appraisal was completed by one investigator using the Cochrane RoB tool, 35 with full checking by one further investigator.
Discrepancies were resolved through discussion, with a third investigator providing consultation if required. Included studies were given an overall rating of 'low', 'unclear' or 'high' RoB dependent on the ratings for individual domains. Ratings given to 'blinding of participants and personnel' and 'blinding of outcome assessment' were excluded from overall assessment of RoB because of the behavioural nature of the interventions and self-reported assessment of outcomes.

| Synthesis of results
Stata v.16 was used for all statistical analyses. 36 Unstandardized mean differences between the intervention and comparator groups and 95% confidence intervals (CIs) were calculated for continuous outcomes and standardized mean differences (Hedges' g) if different measurement tools were reported in the individual studies. Effect sizes for each outcome were combined across studies using random effects meta-analysis. When studies had multiple interventions meeting the inclusion criteria, each estimate of intervention versus comparator was included separately in the meta-analysis, and the comparator group was split between the different interventions to avoid the data in this group contributing more than once to the pooled result (i.e., unit-of-analysis error). When studies reported multiple measures for the same outcome, the measure deemed by the authorship team to be most valid and precise was prioritized and used. Meta-analyses examined effectiveness at intervention-end and 12 months from baseline, regardless of intervention duration. These time points were selected to assess the immediate effect and longer term impact of interventions on mental health outcomes. The potential influence of intervention duration was assessed by subgroup meta-analyses.
For meta-analyses combining unstandardized mean differences, effect sizes based either on post-intervention or change from baseline results were combined in a single forest plot. Separate forest plots were produced for post-intervention and change from baseline when standardized mean differences were used in the meta-analyses. 35 Heterogeneity was assessed using the I 2 statistic and interpreted according to Cochrane recommendations. 35 Contour-enhanced funnel plots of individual study effect sizes were produced for all outcomes to assess the risk of publication bias.

| Additional analyses
Sensitivity analysis was conducted by removing studies judged to be high RoB from pooled estimates to investigate the potential impact on effect estimates. Potential study-level sources of observed heterogeneity between studies in the effect estimates were explored using random effects meta-regression and stratified analyses. Study-level characteristics considered were intervention type (education-only, physical activity-only, education and physical activity), intervention duration (in weeks), intervention delivery mode (face to face, online, resources, telephone, combination), comparator type (inactive, minimal, usual care), comparator intensity (minimal vs. intervention-intensity) and demographic characteristics (e.g., gender and age).

| Study selection
Following deduplication, 31,390 articles were identified for title and abstract screening, with 265 articles eligible for full text screening. Five additional studies were identified through hand searching. Forty-three articles, reporting on 42 studies, met eligibility criteria for inclusion in the review (Figure 1).  Three studies were excluded from the metaanalyses as data were incomplete or unable to be pooled. 45,52,67 Table 1 provides an overview of included studies, and Table S2 presents detailed characteristics for each study. Briefly, studies included a total of 9,385 participants, with the sample size ranging from 23 40 to 1,269. 37 Intervention were compared with no intervention, minimal intervention (e.g., leaflet) or usual care (ranging from minimal to delivery of an intervention). One study did not define what usual care entailed. 71 Overall, the majority of interventions were education based (n = 33), 37

| Risk of bias
Forty-two percent of studies received an overall rating of high RoB, 38  Meta-regression identified that the substantial heterogeneity at intervention-end was explained by one study 48 where the intervention consisted solely of provision of resources (Table S4) ( Figure S49).

| Binge eating
Only one study 66

| Body image concerns
The

| Emotional eating
There was no evidence of a difference between intervention and comparator for emotional eating (post-intervention: SMD −0.12 [95%

| Psychological distress
Only one study reported results for psychological distress at intervention-end (SMD −0.51 [95% CI −0.95, −0.07]), 74 and no studies reported psychological distress data at 12 months from baseline, so no meta-analysis was possible for this outcome.

| Quality of life (global)
There was no evidence of a difference between intervention and  Figures S44 and S45).
Meta-regression identified that the substantial heterogeneity at intervention-end was explained by three interventions 48,69 where 90-100% of intervention participants were women or where the intervention consisted solely of provision of resources (Table S5)

| Quality of life (mental health-related)
Interventions were associated with improvements in mental health-

| Quality of life (obesity-related)
Only one study 60

| Satisfaction with life
There was no evidence of a difference between intervention and

| Self-efficacy (general)
Effect estimates favoured intervention groups for general self-  Figures S44 and S45).  Figure S41), but there was substantial heterogeneity.
Findings were unchanged following exclusion of studies deemed to be at high RoB (n = 5) 43,59,68,75,79 (Figures S44 and S45). There were insufficient studies to conduct meta-regression to identify sources of heterogeneity.
Only one study reported change from baseline results for diet- I 2 = 71%]), but there was substantial heterogeneity. Findings were unchanged after exclusion of studies deemed to be at high RoB (n = 4). 54,55,68,75,79 There were insufficient studies to conduct metaregression to identify sources of heterogeneity.

| Self-esteem
There was no evidence of a difference between intervention and comparator groups for self-esteem at intervention-end (MD 0.95 [95% CI −0.25, 2.15; n = 6; I 2 = 77%]) ( Figure 4). Findings were unchanged following exclusion of studies deemed to be at high RoB (n = 2) 57 ( Figure S46). There were insufficient studies to conduct meta-regression to identify sources of heterogeneity. Only one study reported data for self-esteem at 12 months from baseline (SMD 0.57 [95% CI 0.41, 0.72]), 73 so meta-analysis was not possible.

| Stress
There was no evidence of a difference between intervention and comparator for stress at intervention-end (post-intervention: SMD −0.03 [95% CI −0.40, 0.35; n = 8; I 2 = 77%]) ( Figure 2). Findings were unchanged following exclusion of studies deemed to be at high RoB (n = 3) (Figures S42 and S43). Only one study reported change from baseline results for stress at intervention-end (SMD −5.14 [95% CI −6.34, −3.93]), 70 and no studies reported stress at 12 months from baseline, so meta-analysis was not possible.  33 We found evidence to suggest improvements in mental health-

| Strengths and limitations
To our knowledge, this is the most up-to-date, comprehensive review investigating the effect of weight management interventions on a broad range of mental health outcomes in a representative sample of adults with overweight or obesity. Additionally, this review is the first to investigate whether particular intervention or study characteristics are more supportive of mental health. The methodological approach of this systematic review was rigorous and comprehensive. This review was strengthened by exclusively including RCTs, assessing a broad variety of mental health outcomes and including adults who were representative of the general population with obesity. This review is further strengthened by comparing behavioural weight management interventions to inactive comparator groups or usual care, allowing the review to assess if providing an intervention is more supportive of mental health than not intervening. The impact on mental health was at assessed the end of the intervention to understand the immediate effects, and additionally at 12 months from baseline to explore the sustained effects. Finally, this review aligns with key recommendations for open science and reproducibility of meta-analyses. 83 In particular, the review protocol was preregistered and published, data and methods are comprehensively reported, PRISMA reporting guidelines were adhered to, 29 a librarian was consulted in the search strategy development, and the authorship team included a statistician.
The review findings were limited by the scarcity of eligible evidence, and the high RoB in many included studies. Intervention trials rarely report mental health outcomes in title and abstracts; consequently, the screening process may not have identified all eligible studies. However, investigators conducted extensive hand searching of reviews assessing other outcomes and study reference lists to maximize the inclusion of eligible studies. Review findings were further limited by poor reporting within studies, which made it difficult to conduct stratified analyses and meta-regression for many outcomes.
Despite the comprehensive and inclusive eligibility criteria, the findings of this review are limited to the populations studied in the individual trials. Included studies had a high proportion of female participants and were conducted in middle-high-or high-income countries; this is common for weight management interventions. 84,85 Consequently, how interventions affect the mental health of male participants or adults with obesity in low-middle-or low-income countries remains unclear, as does the impact of other characteristics not represented in the review.

| CONCLUSION
This comprehensive and inclusive systematic review suggests that behavioural weight management interventions result in improvements in a number of mental health outcomes, including body image concerns, depression, mental health-related quality of life, self-efficacy, exercise self-efficacy and diet self-efficacy. This review found no evidence to suggest that interventions negatively impacted mental health; however, there was insufficient evidence to assess the impact on a large number of mental health outcomes at intervention-end and beyond. The review contributes to a growing field of research and makes recommendations to strengthen future intervention studies.
Specifically, future RCTs should ensure inclusion of a broad range of mental health outcomes, transparent reporting of findings, repeated measures over longer durations and comparison with a suitable inactive comparator group. Larger, high-quality studies are required to provide sufficient statistical power to assess differential effects in participant subgroups and to investigate the influential components of interventions.