Supplementary Material for: Supporting Weight Management during COVID-19 (SWiM-C): A randomised controlled trial of a web-based, ACT-based, guided self-help intervention

Introduction: Adults with overweight and obesity are vulnerable to weight gain and mental health deterioration during the COVID-19 pandemic. We developed a web-based, guided self-help intervention based on Acceptance and Commitment Therapy (ACT) that aims to support adults with overweight and obesity to prevent weight gain by helping them to manage their eating behaviours, be more physically active and protect their emotional wellbeing (“SWiM-C”). SWiM-C is a guided self-help programme using non-specialist guides to enhance scalability and population reach while minimising cost. This study evaluated the effect of SWiM-C on bodyweight, eating behaviour, physical activity and mental wellbeing in adults with overweight and obesity over 4 months during the COVID-19 pandemic in the UK.

Methods: We randomised adults (BMI≥25kg/m2) to SWiM-C or to a wait-list standard advice group. Participants completed outcome assessments online at baseline and 4 months. The primary outcome was self-measured weight; secondary outcomes were eating behaviour, physical activity, experiential avoidance/psychological flexibility, depression, anxiety, stress, and wellbeing. We estimated differences between study groups in change in outcomes from baseline to 4 months using linear regression, adjusted for outcome at baseline and the randomisation stratifiers (BMI, sex). The trial was pre-registered (ISRCTN12107048).

Results: 486 participants were assessed for eligibility; 388 participants were randomised (196 standard advice, 192 SWiM-C) and 324 were analysed. The adjusted difference in weight between SWiM-C and standard advice was -0.60kg (-1.67 to 0.47, p=0.27). SWiM-C led to improvements in uncontrolled eating (-3.61 [-5.94 to -1.28]), cognitive restraint (5.28 [2.81 to 7.75]), experiential avoidance (-3.39 [-5.55 to -1.23]), and wellbeing (0.13 [0.07 to 0.18]).

Conclusions: SWiM-C improved several psychological determinants of successful weight management and had a protective effect on wellbeing during the pandemic. However, differences in weight and some other outcomes were compatible with no effect of the intervention, suggesting further refinement of the intervention is needed.

引言：在新冠疫情（COVID-19 pandemic）期间，超重与肥胖成人群体更容易出现体重增加及心理健康状况恶化的情况。我们基于接纳与承诺疗法（Acceptance and Commitment Therapy，ACT）开发了一项基于网络的指导性自助干预方案，旨在通过帮助超重与肥胖成人管理饮食行为、增加体力活动以及维护情绪健康，来预防其体重增加，该方案命名为"SWiM-C"。SWiM-C是一款采用非专业指导者的指导性自助项目，旨在提升干预的可推广性与覆盖人群范围，同时尽可能降低成本。本研究在英国新冠疫情期间，针对超重与肥胖成人开展了为期4个月的随访，评估了SWiM-C对其体重、饮食行为、体力活动及心理健康的影响。

方法：我们将身体质量指数（Body Mass Index，BMI）≥25kg/m²的成人随机分配至SWiM-C组或等待名单标准建议组。受试者在基线及第4个月时完成线上结局评估。主要结局指标为自我测量的体重；次要结局指标包括饮食行为、体力活动、经验回避/心理灵活性、抑郁、焦虑、压力水平及幸福感。我们采用线性回归模型，校正基线结局指标及随机分层因素（BMI、性别）后，估算了两组受试者从基线至第4个月的结局指标变化差异。本试验已预先注册（ISRCTN12107048）。

结果：共486名受试者接受入组资格筛查；最终388名受试者被随机分组（标准建议组196人，SWiM-C组192人），最终324人完成数据分析。校正后，SWiM-C组与标准建议组的体重差异为-0.60kg（95%置信区间：-1.67~0.47，p=0.27）。SWiM-C可改善失控性进食（评分变化：-3.61，95%置信区间：-5.94~-1.28）、认知节制（评分变化：5.28，95%置信区间：2.81~7.75）、经验回避（评分变化：-3.39，95%置信区间：-5.55~-1.23）及幸福感（评分变化：0.13，95%置信区间：0.07~0.18）。

结论：SWiM-C可改善成功体重管理所需的多项心理决定因素，并在疫情期间对受试者的幸福感起到保护作用。但两组在体重及部分其他结局指标上的差异未达到统计学显著性，提示本干预方案仍需进一步优化。