Smartphone-based groups can promote fruit and vegetable consumption and decrease unhealthy snack intake. This study extends previous findings of the benefits of support groups, and sheds light on the temporal dynamics of behavior change.

Compensatory Health Beliefs (CHBs), defined as beliefs that an unhealthy behavior can be compensated for by engaging in another healthy behavior, are assumed to hinder health behavior change. The aim of the present study was to investigate the role of CHBs for two distinct eating behaviors (increased fruit and vegetable consumption and eating fewer unhealthy snacks) with a mixed method approach. Participants (N = 232, mean age = 27.3 years, 76.3% women) were randomly assigned to a fruit and vegetable or an unhealthy snack condition. For the quantitative approach, path models were fitted to analyze the role of CHBs within a social-cognitive theory of health behavior change, the Health Action Process Approach (HAPA). With a content analysis, the qualitative approach investigated the occurrence of CHBs in smartphone chat groups when pursuing an eating goal. Both analyses were conducted for each eating behavior separately. Path models showed that CHBs added predictive value for intention, but not behavior over and above HAPA variables only in the unhealthy snack condition. CHBs were significantly negatively associated with intention and action planning. Content analysis revealed that people generated only a few CHB messages. However, CHBs were more likely to be present and were also more diverse in the unhealthy snack condition compared to the fruit and vegetable condition. Based on a mixed method approach, this study suggests that CHBs play a more important role for eating unhealthy snacks than for fruit and vegetable consumption.

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IntroductionBehaviour change is key to the public health measures that have been issued in many countries worldwide to contain COVID-19. Public health measures will only take preventive effect if people adhere to them. Interventions taking health psychology approaches may promote adherence to public health measures. However, evidence from randomised controlled behaviour change trials is scarce during an ongoing pandemic. We aim to use the example of hand washing with soap to optimise and test a digital, theory-based and evidence-based behaviour change intervention to prevent the spread of COVID-19.Methods and analysisThis protocol describes the multiphase optimisation strategy for the preparation, optimisation and evaluation of a theory-based and evidence-based intervention delivered via app. The app aims to promote correct hand hygiene at key times in the adult general population. The study will be conducted in German-speaking Switzerland. The preparation phase has identified relevant behavioural determinants of hand hygiene during a pandemic from health behaviour theories and formative research with focus groups (n=8). The optimisation phase will identify the most effective and acceptable combination and sequence of three intervention modules in a parallel randomised trial (n=387) with analysis of variance (ANOVA) and regression analysis. Additionally, thematic analysis of qualitative interview data (n=15) will be used to gain insights on the feasibility, usability and satisfaction of the intervention. The evaluation phase will test the optimised intervention against an active control group in a randomised controlled trial (n=205), analysing pre-post differences and 6-month follow-up effects with ANOVA and regression analysis.Ethics and disseminationThe trial was approved by the Cantonal Ethics Commission Bern of the Swiss Association of Research Ethics Committees (protocol ID: 2021-00164). Final results will be presented in peer-reviewed journals and at conferences.Trial registration numberNCT04830761.

Compensatory health beliefs (CHBs) are a means to cope with motivational conflicts between intended health goals and the temptation for an unhealthy behavior. As CHBs can fluctuate on a daily basis, this study examined how daily CHBs are associated with daily intention to quit smoking and daily number of cigarettes smoked before and after a quit date at the between- and within-person level. The study comprised a prospective longitudinal design and investigated 83 women and 83 men for 32 consecutive days during an ongoing joint self-set quit attempt. Daily CHBs varied from day to day and between individuals. At the between-person level, higher women’s mean CHBs were associated with lower intention (b = −0.23, p = 0.04) and at the 10% level with more cigarettes smoked after the quit date (rate ratio (RR) = 1.92, p = 0.07). At the within-person level, women’s higher than usual CHBs were unrelated to intention to quit, but were related to less smoking before (RR = 0.96, p = 0.03) and at the 10% level after the quit date (RR = 0.91, p = 0.09). A marginally positive association between daily CHBs and smoking at the within-person level emerged for men. The negative effect of daily CHBs at the between-person level on smoking seems to unfold after the quit attempt and for women only.