Objective: Weight management interventions can affect mental health. Mental health can affect engagement with weight loss interventions or services. This study explored mental health and wellbeing outcomes, retention and participant experiences of mental health within the Game of Stones trial. Methods: Mixed methods process evaluation within a 3-group randomised controlled trial: behavioural text messages with financial incentives, texts alone, and waiting list control, for 585 men with obesity. Secondary outcomes analysed descriptively included: Warwick-Edinburgh Mental Wellbeing Scale, Weight Self-Stigma Questionnaire, EQ-5D-5L, EQ-5D-5L anxiety and depression subscale, Patient Health Questionniare-4, and retention. Three categories of participants were compared: ever diagnosed with a mental health condition (n=146; 25.0%), latent mental health condition (n=142; 24.3%) no mental health condition (n=295; 50.6%). Semi-structured interviews (n=54) were conducted after 12 months and analysed using Framework method. Results: A higher proportion of men who self-reported ever having a mental health condition had a disability, multiple long-term conditions, were under financial strain and were single compared to those with those with a latent mental health condition and no mental health condition . Improvements from baseline were shown for weight stigma, wellbeing and PHQ-4 at 12 months for men in intervention groups with a mental health condition and latent mental health condition. EQ-5D-5L Visual Analogue Scale scores improved across all mental health categories and trial groups, but EQ-5D-5L and EQ-5D-5L-AD scores were inconsistent. Retention at 12 months was 76.0% (mental health condition), 70.4% (latent mental health condition) and 72.5% (no mental health condition). The qualitative evidence indicated that stress, anxiety and depression were experienced in different ways by men during the programme. Mental health difficulties were unique to the individual, could be episodic, recurrent, cyclical or ongoing and were a barrier to behaviour change for some but not for others. Conclusion: The trial was able to engage and retain men regardless of mental health category. Behavioural text messages with or without incentives helped some men lose weight, but not others. Observed heterogeneity for mental health and wellbeing measures is problematic for weight management trials with men.

The authors have declared no competing interest.

ISRCTN91974895

This trial was funded by the National Institute for Health and Care Research (NIHR), UK (Ref: NIHR 129703) using UK aid from the UK Government to support global health research. The research team were invited to apply for additional funding from NIHR in 2021 to investigate UK policy priority areas: mental health conditions and multiple long-term conditions within the Game of Stones trial. The views expressed in this publication are those of the authors and not necessarily those of the NIHR or the UK government. This project was supported by NHS Bristol, North Somerset and South Gloucestershire Integrated Care Board; NHS Greater Glasgow and Clyde; NRS Primary Care Network and HSC R&D Division of the Public Health Agency [HSC R&D Award Reference PHR Project: NIHR129703].

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Ethical Approval for the Game of Stones trial was received from the North of Scotland Research Ethics Committee 2 [20/NS/0141].

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