A cluster randomized controlled trial of a brief positive healthy eating intervention

Abstract

Excessive sugar intake poses a significant risk factor for non-communicable diseases. A positive healthy eating (PHE) intervention was developed to promote low-sugar dietary practices in families. The PHE intervention capitalized on positive psychological constructs to overcome barriers to health behavior change by helping families associate feelings of joy, gratitude, and savoring with healthy eating. In a cluster randomized controlled trial, 1983 participants from 1467 families were recruited in Hong Kong. PHE included a core and booster session. Data were collected at pre-intervention, post-intervention, and at 1-month and 3-month follow-up. Compared to the control, PHE showed greater increase in intention to change at post-intervention, engagement in low-sugar dietary practices individually and with family members at 3-month follow-up, and greater reduction in sugar-sweetened beverage intake at 1-month and 3-month follow-up. Intentions to change mediated PHE’s effects on low-sugar dietary practices. Focus group interviews revealed the behavior-change process and family quality of life.

Keywords

community-based intervention healthy diet healthy eating positive psychology randomized controlled trial

Introduction

High consumption of free sugar is a significant risk factor for numerous non-communicable diseases (Biswas et al., 2022). Sugar-sweetened beverages, such as carbonated sodas, flavored juices, and drinks with added sugar, contribute to excessive sugar intake in many diets (Malik and Hu, 2019). They have little nutritional value and add to the increased caloric intake from high-calorie foods that are often consumed together. Unhealthy diets characterized by sugar-sweetened beverage consumption are a significant contributor to increased blood pressure, liver and muscle fat accumulation, as well as higher risk of gout, type 2 diabetes, hypertension, stroke, coronary heart disease, and pancreatic cancer (Pietrantoni and Mayrovitz, 2022; Yin et al., 2023). Additionally, dietary intake of added sugar in processed or prepared foods has significant harmful effects on cardiometabolic health, increasing the risk of cardiovascular-related mortality (Moore and Fielding, 2016). People generally do not compensate for increases in sugar intake from drinks with a decrease in energy from solid foods, so their adverse effects are additive. Metabolic syndrome is a potential mechanism linking sugar intake to coronary heart disease, stroke, and type 2 diabetes (Malik and Hu, 2019).

Non-communicable diseases, such as cardiovascular diseases and diabetes, that are attributable to excessive sugar intake have led to an estimated 20 million deaths around the world each year (NCD Countdown 2030 Collaborators, 2018). Free sugar consumption exceeds the optimal level in nearly every country (GBD 2017 Diet Collaborators, 2019), with 54% of people consume sugar-sweetened beverages on a daily basis (Malik and Hu, 2019). These trends are supported by the increased per capita sales of soda in many countries, such as China where sales increase by nearly 20% per year (Yin et al., 2023). These statistics highlight the detrimental impact of poor dietary habits on non-communicable disease morbidity and mortality worldwide. The prevalence of unhealthy dietary patterns associated with excessive sugar intake underscores the urgent need for feasible and cost-effective interventions to promote low-sugar dietary practices.

Existing interventions targeting healthy diets (HD) generally involve promoting the intake of healthy foods (e.g. fruits and vegetables, healthy snacks, and low fat foods) or reducing the intake of unhealthy foods (e.g. fatty, salty and sugary foods, and sugar-sweetened beverages; Adriaanse et al., 2011; Carrero et al., 2019). For example, a 6-month health literacy intervention provided education on the recommendations for beverage categories with the primary goal of reducing sugar-sweetened beverage consumption (Zoellner et al., 2016). A 30-day in-person and online coaching intervention with multi-components (e.g. goal setting, action planning, self-monitoring, and coaching) was designed to reduce free sugar consumption (Brittain et al., 2021). A 6-week behavioral intervention used experiential learning (e.g. sampling flavored water, exploring the grocery store, and managing triggers) to reduce sugar-sweetened beverage and increase in water intake (Wang et al., 2016). However, there are a number of deficiencies among existing interventions that warrant further investigation and development. A majority of these HD interventions were designed for children or students (Carrero et al., 2019) even though the burden of disease attributable to poor dietary habits is highest among adults. Moreover, they are mostly individual-based, disregarding the role of social environment on healthy eating practices that has consistently been found in the literature (Campbell et al., 2007; Wijayaratne et al., 2018). Besides, existing HD interventions require a high level of commitment from interventionists and the service target, ranging from several months to more than 1 year, to initiate the behavior change process, but the effects in improving HD were modest or null (Samdal et al., 2017). Attempts to reduce sugar intake using brief educational interventions had been ineffective (Griffin et al., 2015). Meta-analyses of HD interventions showed that existing techniques for behavior change lacked empirical support in improving dietary outcomes (McDermott et al., 2016; Spring et al., 2021). Solutions that consider the approach, feasibility, and efficacy to improve public health are therefore direly needed.

Brief interventions that have shown promising results in promoting positive lifestyle changes and building sustainable habits for better quality of life can be found in the positive psychology literature. Positive psychology interventions involve simple activities that are enjoyable in its own right and can be integrated into daily routine to cultivate positive attitudes and mindset and promote proactive behaviors for a happy, engaged, and meaningful life (Seligman et al., 2005). These interventions target cognitive (Schueller, 2010), social (Seligman et al., 2006), and behavioral changes (Burton and King, 2004) through writing something down, thinking about something, saying something to someone, engaging in some task, or a combination of these. Because positive psychology exercises are pleasurable and enjoyable to do, even low-dose intervention programs showed continued adherence to the activities during and after the intervention period (Ho et al., 2017). Extant research showed that positive psychology interventions are effective for promoting well-being and mental health (Hendriks et al., 2020). The positive psychology approach can be applied to the family context to enhance family strengths and resilience for optimal family functioning (Sheridan et al., 2004). Positive family interventions have generated evidence of effectiveness in quasi-experimental studies (Ho et al., 2016c) and randomized controlled trials (Ho et al., 2016a, 2016b), demonstrating that positive psychological constructs (e.g. gratitude, flow, happiness, and savoring) can be capitalized in the family environment and adapted for family activities to enhance family communication, family well-being, and subjective happiness.

Both positive psychological constructs and well-being have been linked to physical health and health-promotion behaviors. There is mounting evidence that subjective well-being positively impacts physical health, including improved general health, immune functioning, cardiovascular functioning, and longevity (Howell et al., 2007). It is speculated that people who are happier are more likely to engage in health-promotion behaviors and thus have better physical health. For example, studies showed that optimists tend to hold positive attitudes about health-promotion behaviors, perceive control over their health, and adhere to health recommendations (Dubois et al., 2012). Despite the linkage between positive psychological constructs and physical health, the existing literatures on health behavior change interventions and positive psychology interventions have been largely unconnected. There has been an absence of utilizing positive psychological constructs as an intervention mechanism to promote physical health.

In bringing together the two disconnected fields of research, we launched the Happy Family Kitchen Movement (HFKM) project to develop and implement a series of community-based family intervention programs that integrate positive psychological constructs with health-promotion family activities for family holistic health (Ho et al., 2020b). A cluster randomized controlled trial was conducted to test whether brief family interventions with positive psychological constructs of joy, gratitude, and savoring can help families overcome barriers to healthy lifestyle change. We provided initial evidence that a brief positive physical activity (PPA) intervention is effective for promoting physical activity and physical health among individuals and families (Ho et al., 2020a).

To provide evidence on the universality of the positive psychology approach across health-promotion behaviors, it is theoretically and practically important to verify the utility of positive psychological constructs in cultivating different types of lifestyle change. The intervention described in the present article, namely, positive healthy eating (PHE), targeted low-sugar dietary practices to address the global non-communicable disease pandemic linked to excessive sugar intake (Biswas et al., 2022; Moore and Fielding, 2016). PHE leveraged positive affective experiences to overcome barriers to health behavior change by helping families associate feelings of joy, gratitude, and savoring with HD. This approach is in line with the upward spiral theory of lifestyle change (Van Cappellen et al., 2018), which states that associating positive affective experiences with health behaviors such as HD increases one’s intention to engage in that activity and actual engagement in it. The effect of positive affect (i.e. perceiving a health behavior as enjoyable) was found to be stronger than the effects of positive cognition (i.e. perceiving a health behavior as beneficial) emphasized in health behavior change models (Lawton et al., 2009). The theory further posits that as individuals engage in health behaviors that are enjoyable, the pleasant behaviors are likely to be repeated and maintained, creating more positive affective experiences and forming an upward spiral toward a healthy lifestyle (Van Cappellen et al., 2018). Positive emotions experienced during HD are therefore expected to initiate non-conscious motives to reenact them, which in turn guides attention and decision to future engagement in HD. To create positive affective experiences during HD, we adopted the positive psychological constructs of joy, gratitude, and savoring that have been tested in family activities (Ho et al., 2016c). The joy theme emphasized short-term pleasures and long-term gratifications from HD and HD with family members, the gratitude theme involved the expression of thankfulness and appreciation to family members for engaging in and enjoying HD together, and the savoring theme focused on enjoying and cherishing the present moment and the quality time spent engaging in HD with family members. Unlike existing HD interventions, PHE is brief, appropriate for all age groups, and can be implemented by non-health professionals to increase public health impact.

This study adopted a mixed-methods design in a cRCT. It aims to test the hypotheses that integrating positive psychology with health promotion would be effective as an HD intervention for (H1) promoting the intention to adopt low-sugar dietary practices individually and with family members, (H2) increasing engagement in low-sugar dietary practices individually and with family members, and (H3) reducing sugar consumption from sugar-sweetened beverages. With reference to existing health behavior change interventions (Albarracín et al., 2018; Dusseldorp et al., 2014; Michie et al., 2009), this study explores whether the intentions to adopt low-sugar dietary practices are mechanisms of change underlying the intervention’s effects on low-sugar dietary behaviors. To enrich the study findings, focus group interviews were conducted to provide in-depth insights into the motivating factors of health behavior change and the behavior change process among families. By collecting both quantitative and qualitative data, this study can rigorously unravel the effectiveness of the PHE intervention on target outcomes and elucidate the psychosocial processes that drive cognitive, attitudinal, and behavioral changes within the family context (Chu et al., 2018).

Methods

Participants

The HFKM (Ho et al., 2020b) was a citywide intervention project implemented in all 18 districts in Hong Kong. The project was carried out during May 2015 to October 2016. To maximize the application of research findings to a larger population (Spoth et al., 2002), more inclusive eligibility criteria were used: (a) Cantonese speaking (the common local dialect); (b) intact verbal and hearing abilities for interpersonal communication; (c) reading and writing abilities for questionnaire completion; (d) ages 12 or older for participation in the intervention evaluation; and (e) attending the program sessions with one or more family members. Meta-analyses of health behavior change interventions showed small effect sizes for dietary change (Albarracín et al., 2018; Dusseldorp et al., 2014; Michie et al., 2009). Also, the attrition rate for positive family interventions with multiple time-points and family members was up to 50% at follow-up (Ho et al., 2016a, 2016c). Thus, to detect small effect sizes (Cohen’s d = 0.20), to achieve a statistical power of 0.80 and an alpha of 0.05, and to account for up to a 50% attrition rate (Campbell et al., 2004), a minimum sample size of 1920 participants was needed. With support from local social service organizations, the Social Welfare Department, kindergartens, and primary schools, a total of 4198 individuals were invited, and 1983 eligible participants from 1467 families participated in the study.

Multimodal approaches were used to recruit study participants through social service organizations, the Social Welfare Department, and schools: (a) promotional materials such as posters, banners, leaflets, and publications; (b) phone invitations; (c) face-to-face invitations; (d) promotion through websites and e-mails; (e) home visits; and (f) referrals from social service workers and teachers. Written informed consent was obtained prior to participation. For participants under the age of 18, written consent was obtained from the adult next of kin, caretakers, or guardians on their behalf. Each family received two HK$50 (about US$13) supermarket gift vouchers as an honorarium for participation. The Institutional Review Board of the University of Hong Kong/Hospital Authority Hong Kong West Cluster granted ethics approval (UW 15-083). The study was preregistered in ClinicalTrials.gov (NCT02563613).

Procedures

A 2.5-day train-the-trainer workshop was delivered to prepare social workers and teachers from the participating social service organizations and schools for designing and delivering community programs. The trainers included clinical psychologists, registered social workers, a registered nurse, and academic researchers. The workshop covered the contents of positive psychology, low-sugar dietary practices, program design, and program evaluation. The trainees learned about the positive psychology concepts (i.e. joy, gratitude, and savoring), the guidelines for low-sugar consumption, and reading the food nutrition labels. Sample activities of the intervention were demonstrated with the trainees (e.g. competition on determining the low, medium, and high sugar content from nutrition labels). Through hands-on experiential learning, the trainees learned to design and deliver family-friendly activities that utilize positive psychology approaches to encourage health-promotion behaviors. For quality assurance and enhancement, the project team provided trainees with supervision, consultation, and a practice manual (including the intervention materials, a cookbook for healthy eating, and a program rundown to standardize the content and duration) to guide the planning and implementation stages of the community programs.

A total of 54 social service units and schools (from 28 non-governmental organizations, 1 government department, and 7 schools) were randomized in a 3-arm cRCT: positive physical activity (PPA, intervention arm 1), positive healthy eating (PHE, intervention arm 2), and control (C, waitlist control arm). The randomization procedure was conducted at a cluster level using computer-generated random numbers (allocation ratio of 1:1:1). Individual allocation was not practicable within organizations and families because it could result in contamination or spillover among members of the same cluster. The participants were not informed about the study design and the existence of other groups in the study. For the PHE group (consisting of 19 clusters, 665 participants), the participants received a core session of about 2 hours, followed by a booster session of about 1 hour, 1 month later. For group C (consisting of 20 clusters, 790 participants), the participants received a tea gathering session at the beginning and 1 month later. The core session in PHE consisted of group activities and homework assignments on positive psychology and HD; the booster session in PHE involved the consolidation of knowledge and skills obtained from the core session; the tea gathering sessions included activities unrelated to the intervention, such as arts and crafts workshops. The effectiveness of the PPA intervention (consisting of 15 clusters, 528 participants) was reported elsewhere (Ho et al., 2020a). This paper focuses on the PHE intervention.

Structured questionnaires were administered at pre-intervention (baseline assessment, T₁), immediately after the core session (T₂), 1-month follow-up after the core session (before the booster session, T₃), and 3-month follow-up after the core session (T₄). Consolidated Standards of Reporting Trials (CONSORT, Figure 1; Egger et al., 2001) shows that the retention rate for PHE was 97.6% at T₂, 81.5% at T₃, and 68.7% at T₄, whereas for control, it was 99.5% at T₂, 87.2% at T₃, and 75.4% at T₄. The questionnaires were self-administered with standardized instructions to avoid researcher bias.

Figure 1.

*15 clusters (n = 528) were allocated to a positive physical activity group, reported in Ho et al 2020b.

Semi-structured focus group interviews were conducted after the cRCT. Purposive sampling was used to recruit participants who attended the core and booster sessions in PHE. Overall, two trained interviewers conducted 11 focus groups (PPA: 4, PHE: 5, C: 2) consisting of 92 participants (PPA: 33, PHE: 43, C: 16). Semi-structured interview guidelines and prompts were developed according to the standard focus-group protocol to cover a range of key issues pertaining to the research questions (Krueger and Casey, 2014). The focus groups were conducted with flexibility to allow unanticipated themes to emerge. The group discussions, which were audio recorded, lasted for about 60 minutes in a quiet venue at the participating organizations’ community centers, social service centers, and primary and secondary schools. A HK$50 (about US$6) supermarket gift voucher was given to each participant as an honorarium for participation.

Intervention programs

Trained social workers and teachers designed and implemented the PHE programs in the community. The interventionists were given flexibility to choose and focus on one of three positive psychology themes (i.e. joy, gratitude, and savoring) to cater to the unique needs of their service recipients from the social service organizations and schools. The intervention objective was consistent across programs regardless of the chosen theme, which was to promote low-sugar dietary practices at an individual and family level. Allowing the interventionists to determine the theme of the intervention while adhering to a common intervention objective can enhance the feasibility of the program in community settings (Ho et al., 2016a, 2016c). The intervention programs were held at the participating organizations’ community centers, social service centers, and primary and secondary schools located across 18 districts in Hong Kong. Thus, the participants were familiar with the environment and interventionists to control for contextual confounds.

Low-sugar dietary practices both individually and with family members were promoted through positive psychology themes. Three target behaviors were designed for each theme to guide the group activities and homework assignments so that HD could be encouraged, reinforced, and sustained. The joy theme involved (a) sharing happy experiences in HD with family members, (b) discovering joy during HD, and (c) reminiscing about an HD experience that made one or one’s family happy. The gratitude theme involved (a) appreciating the strengths of family members during HD and expressing gratitude to family members for enjoying healthy meals together through (b) words and (c) actions. The savoring theme involved (a) paying attention to the process of HD, (b) savoring the moment of HD, and (c) treasuring quality time during HD with family members (Ho et al., 2020b).

The programs were consisted of psychoeducation and experiential learning. Participants were introduced the WHO guidelines for low-sugar consumption (Breda et al., 2019) and were taught to read nutrition labels of foods and beverages and calculate the sugar content to strengthen their awareness and knowledge in identifying low sugar products. Simple warm-up exercises were conducted to facilitate their learning, such as guess the sugar content of common beverages and sweetness tasting blindfold challenge. Moreover, participants engaged in the target behaviors during the program sessions through experiential learning, whereby group activities were implemented to create a positive environment for family members to interact, experience positive emotions, and utilize character strengths. For example, the interventionist provided low-sugar healthy recipes for Chinese cuisines, soups, salads, and desserts for families’ preparation. Family members prepared and consumed a low sugar meal together and shared their joyful experience with other participants. To help participants develop low-sugar consumption into habitual behaviors, they were encouraged to practice the target behaviors at home by completing homework assignments. For example, participants were asked to keep a food diary to record their food and beverage intake and the actions taken to sustain their healthy eating goals in the family.

Before conducting the main study, the intervention programs were subjected to pilot testing. The purpose of the pilot test was to assess the validity, reliability, feasibility, suitability, and desirability of the program content, schedule and duration, interactive games and activities, target behaviors, and outcome measures. A total of 56 participants from two participating organizations were involved in the pilot testing phase.

In order to maintain adherence to the guiding principles and increase consistency and quality of the intervention programs, the social service units and schools participating in the project were required to submit program proposals to the project steering committee. This committee consisted of leading academic researchers from the project team, as well as leaders from the participating organizations. The proposals were reviewed and feedback was provided for revision. Once the suggested improvements were incorporated, all final proposals were approved for implementation. Onsite process evaluation (Ho et al., 2020a) showed that there was a high degree of adherence in the delivery of core messages in the core (85.5%) and booster sessions (87.8%) of the intervention programs. On a scale of 1–5, the activities designed by the interventionists for the core (M = 3.99, SD = 0.74), booster (M = 4.09, SD = 0.62), and tea gathering sessions (M = 4.00, SD = 0.58) were of high quality. Moreover, the participants showed a high level of engagement in practicing the target behaviors during the core (M = 3.87, SD = 0.67) and booster sessions (M = 4.00, SD = 0.64).

Measures

Intentions to change

The intention to adopt low-sugar dietary practices individually and with family members were rated on a 5-point scale, ranging from 1 (no intention at all) to 5 (very much intended), at T₂. The operational definition of low-sugar consumption based on WHO guidelines (i.e. “low sugar refers to foods and drinks that contain no more than 5 grams of sugar per 100g”; Breda et al., 2019) was provided to improve the validity of the measure. The items on intentions to change adapted to specific health-promotion activities have demonstrated a responsiveness to change in our previous community-based interventions and training programs (Lai et al., 2017; Zhou et al., 2016).

Low-sugar dietary practices

Participants self-reported the frequency of low-sugar dietary practices individually and with family members in the past 4 weeks on an 11-point scale, ranging from 0 (never) to 10 (very frequently), at T₁, T₃, and T₄. The operational definition of low-sugar consumption based on WHO guidelines (i.e. “low sugar refers to foods and drinks that contain no more than 5 grams of sugar per 100g”; Breda et al., 2019) was provided to improve the validity of the measure. Self-rated single-item measures of HD have demonstrated test-retest reliability, convergent validity against other measures of food consumption, and concurrent validity against risk factors for cardiometabolic disease (Gattshall et al., 2008; Sullivan et al., 2021). We used this approach to assess health behavior change among individuals and families in our previous health-promotion interventions, which has demonstrated intended differences between conditions, providing support for criterion validity (Ho et al., 2020a).

Sugar-sweetened beverage intake

The intake of sugar-sweetened beverages was assessed by asking participants to report the frequency and amount of beverage items consumed at T₁, T₃, and T₄. The items were adapted from the Beverage Intake Questionnaire (BEVQ; Hedrick et al., 2012) to include popular beverages in the local context. Beverage categories were determined according to the sugar content in beverages provided by the Centre for Food Safety of Hong Kong Special Administrative Region (2009): (1) high sugar content (e.g. red bean icy drink, tri-color icy drink, and cola); (2) moderate sugar content (e.g. iced milk tea with pearl tapioca, iced chocolate drink, and iced coffee); and (3) low sugar content (e.g. low sugar soybean milk, “less sweet” coffee, and “less sweet” lemon tea). The frequency of beverage consumption was rated by the average consumption of each kind of beverage in a week (0 = never; 6 = 3 times per day). The amount of beverage consumption was rated by the average consumption of each kind of beverage each time (1 = 0.5 cups (equivalent to about 100 ml); 5 = 2.5 cups (equivalent to about 500 ml)). Total sugar-sweetened beverage consumption was computed by summing the total sugar content in grams for each category consumed per day.

Data analysis

Quantitative data were analyzed using SPSS 25.0. By intention-to-treat (ITT) analysis (Fisher et al., 1990), the expectation-maximization (EM) algorithm estimation was used to treat missing data, which provides robust and unbiased estimates under missingness conditions (Graham et al., 1996). Complete-case analysis was conducted as sensitivity analysis (see Supplemental Materials). Pearson’s chi-square tests and linear mixed models were conducted to examine comparability among the groups in terms of baseline demographic characteristics and other measures, which showed that the two groups were not significantly different by sex, age, education level, and baseline scores of low-sugar dietary practices, low-sugar dietary practices with family members, and total consumption of sugar-sweetened beverages. To evaluate program effectiveness, linear mixed models were conducted with group allocation as a fixed effect (i.e. PHE and C) and clustering of individuals (level 1) within families (level 2) and programs (level 3) as random effects. The dependent variables were intentions to change at T₂, low-sugar dietary practices at T₃ and T₄, and intake of sugar-sweetened beverages at T₃ and T₄. Sex, age, education level, and baseline measures were accounted for in the analysis. Between-group differences in the outcome changes (i.e. PHE vs C) and within-group changes across time were examined (i.e. T₁ vs T₃, T₁ vs T₄). The linear mixed model is expressed below (Laird and Ware, 1982):

y_{i j} = β_{0} + β_{1} X_{1 i j} + b_{i 1} Z_{1 i j} + ε_{i j}

(1)

b_{i k} \sim N (0, ψ_{k}^{2}), Cov (b_{k}, b_{k'}) = ψ_{k k'}

(2)

ε_{i j} \sim N (0, σ^{2} λ_{i j j}), Cov (ε_{i j}, ε_{i j'}) = σ^{2} λ_{i j j'}

(3)

where $y_{i j}$ denotes the response for member j of cluster i, $β_{0}$ denotes the fixed intercept, $β_{1}$ denotes the fixed-effect parameter, $X_{1 i j}$ denotes the fixed-effect predictors, $b_{i 1}$ denotes the random-effect parameter, $Z_{1 i j}$ denotes the random-effect predictors, $ε_{i j}$ denotes the error term, $ψ_{k k'}$ denotes the covariances among the random effects, and $σ^{2} λ_{i j j'}$ denotes the covariances between error terms in cluster i.

Mediation was conducted as secondary analysis to explore whether the intentions to adopt low-sugar dietary practices are mechanisms of change underlying PHE’s effects on low-sugar dietary behaviors. The mediation model included the treatment condition as the predictor, intentions to change at T₂ as the mediator, and low-sugar dietary practices and intake of sugar-sweetened beverages at T₃ and T₄ as the outcomes. The control variables included sex, age, education level, and baseline measures. Indirect effects were tested using the bootstrap method to produce 95% bias-corrected confidence intervals based on 10,000 bootstrap samples (Hayes, 2017). The direct and indirect effects of the treatment condition are derived from two linear models expressed below:

M_{1} = i_{M} + a_{i} X + e_{M}

(4)

Y = i_{y} + c_{1}^{'} X + \sum_{i = 1}^{k} b_{j} M + e_{y}

(5)

Qualitative data were analyzed using thematic analysis (Braun and Clarke, 2006). The recorded interview sessions were transcribed verbatim into Chinese. Transcripts were read in detail and patterns of meaning within the data were identified, examined, and recorded. An in-depth analysis was conducted using the process of constant comparisons to identify the frequently recurring words, phrases, and sentences in the transcription. The ideas were organized into codes and formed into over-arching themes to represent a group of categories. To enhance the trustworthiness and credibility of the coded themes, a panel of two researchers independently performed the coding analysis. Consensus was reached by reanalyzing the themes and reviewing the codes when needed.

Results

Intervention effectiveness

Comparing between groups, PHE rated significantly higher on intention to adopt low-sugar dietary practices (M = 4.21, SD = 0.71; b = 0.29, SE = 0.05, p < 0.001, d = 0.35) and intention to adopt low-sugar dietary practices with family members at T₂ (M = 4.24, SD = 0.68; b = 0.25, SE = 0.05, p < 0.001, d = 0.30) than control (M = 3.92, SD = 0.94 and M = 3.98, SD = 0.93, respectively). Table 1 shows that PHE’s engagement in low-sugar dietary practices (b = 0.50, SE = 0.14, p < 0.001, d = 0.23) and engagement in low-sugar dietary practices with family members (b = 0.49, SE = 0.14, p < 0.001, d = 0.23) had significantly increased at T₄ compared to control. Furthermore, PHE’s reduction in sugar consumption from sugar-sweetened beverages at T₃ and T₄ was significantly greater than that of control (b = −2.53, SE = 1.14, p = 0.03, d = 0.12 and b = −1.98, SE = 0.97, p = 0.04, d = 0.11, respectively).

Table 1.

Effectiveness of PHE as estimated by linear mixed modeling.

	Time point	PHE M (SE)^a,b	Control M (SE)^a,b	Between-group difference
	Time point	PHE M (SE)^a,b	Control M (SE)^a,b	b (SE)^b	Cohen’s d^c
Low sugar diet	T₁	5.98 (0.10)	5.66 (0.14)	—	—
	T₃	6.04 (0.09)	5.76 (0.13)	0.28 (0.15)	0.12
	T₄	6.15 (0.08)	5.64 (0.12)	0.50 (0.14)***	0.23
Low sugar diet with family	T₁	5.78 (0.10)	5.44 (0.14)	—	—
	T₃	6.02 (0.09)*	5.86 (0.12)*	0.15 (0.15)	0.07
	T₄	6.19 (0.08)***	5.71 (0.11)	0.49 (0.14)***	0.23
Sugar-sweetened beverage	T₁	19.37 (0.89)	18.06 (0.82)	—	—
	T₃	16.26 (0.84)**	18.79 (0.77)	−2.53 (1.14)*	0.12
	T₄	14.48 (0.71)***	16.47 (0.66)*	−1.98 (0.97)*	0.11

Analysis controlled for age, sex, and education level.

Statistical significance indicates within-group change from T₁.

*p < 0.05. **p < 0.01. ***p < 0.001.

Cohen’s d.

For within-group effects, Table 1 shows the significant within-group increases from baseline in PHE on engagement in low-sugar dietary practices with family members at T₃ and T₄ (p = 0.02, d = 0.11 and p < 0.001, d = 0.19, respectively) as well as significant within-group reductions from baseline in sugar consumption from sugar-sweetened beverages at T₃ and T₄ (p < 0.01, d = 0.12 and p < 0.001, d = 0.22, respectively). Control showed a significant within-group increase from baseline on engagement in low-sugar dietary practices with family members at T₃ (p = 0.01, d = 0.17) as well as a significant within-group reduction from baseline in sugar consumption from sugar-sweetened beverages at T₄ (p = 0.02, d = 0.09).

Mediation analysis showed that the intentions to change at T₂ significantly mediated the effects of PHE on engagement in low-sugar dietary practices (b = 0.07, SE = 0.03, 95% CI [0.019, 0.138]; b = 0.08, SE = 0.03, 95% CI [0.026, 0.146], respectively) and engagement in low-sugar dietary practices with family members at T₃ and T₄ (b = 0.11, SE = 0.03, 95% CI [0.046, 0.180]; b = 0.10, SE = 0.03, 95% CI [0.041, 0.159], respectively). The indirect effect on sugar consumption from sugar-sweetened beverages at T₃ and T₄ was non-significant.

Qualitative results on low-sugar dietary practices

Table 2 summarizes the themes, subthemes, sample quotes, and the corresponding frequencies among the focus groups and participants. The focus group interviews showed that the participants experienced a behavior change process toward low-sugar dietary practices after participating in the PHE program. The participants frequently reported cognitive change toward healthy eating and developing healthy eating habits individually and with family members as a result of the intervention.

Table 2.

Themes, subthemes, and sample quotes derived from focus group interviews.

Theme	Subtheme	Examples	Frequency (FG)	Frequency (p)
Low-sugar dietary practices	Cognitive change toward healthy eating	“(We) have a diet with lower salt and lower sugar. Before joining the program, I tended to choose sugary drinks and sugary foods because I like sweets. I started to choose low-sugar options after joining the program because the health lessons learned (from the program) are deeply ingrained in my mind: ‘eat less sugar, don’t buy sugary foods.’” (A mother, middle age) “After joining this program, I observed an obvious change in my son. Sometimes when he is eating breakfast, he asks, ‘Mommy, is this healthy?’ ‘What will happen if I eat this?’ He didn’t ask these questions before and wasn’t curious about it. . . he grasped the concept of healthy eating.” (A mother, young adult)	5 (100%)	26 (60.5%)
Low-sugar dietary practices	Developing healthy eating habits	“He (my son) pays more attention than I do to checking sugar content (from food labels). He reminds me about what is healthy and unhealthy. We didn’t read the food labels before, and we weren’t concerned about sugar content. He bears it in mind now.” (A mother, young adult) “I used to add sugar when I stir fried vegetables and other dishes. Now, I listen to my son when he reminds me, ‘Mom, you forget again. Don’t add sugar.’ It’s the same for buying drinks. My elder son likes sugary and fizzy drinks. My younger son would ask his brother not to buy those drinks because they are high in sugar content.” (A mother, middle age)	5 (100%)	28 (65.1%)
Family quality of life	Family bonding	“In fact, we seldom had a chance to join this kind of activity together as a family. This program enabled my daughter, son, husband, and I to do something together. . . It provided us with an opportunity to get together.” (A mother, young adult) “(The program) is especially suitable for my younger daughter who has started to talk more and developed a more harmonious relationship with me. Our thoughts were not aligned before because she was raised by her grandmother at a young age. But the situation is getting better, and she is willing to talk to me at least.” (A mother, young adult) “My mom and I read (the food labels) together, which has created more topics for us to discuss.” (A mother, middle age)	5 (100%)	26 (60.5%)
Family quality of life	Positive affective experiences	“Previously, I was always the one who praised him (my son) . . . but now he takes the initiative to praise me first. (The program) is quite unique in that children can learn about being appreciative.” (A mother, young adult) “For instance, sometimes when grandmother cooks a healthy meal for her (my daughter), she would write a thank you note saying, ‘Thank you, grandma! Your cooking is fantastic.’ It is very considerate and we feel touched by it. It’s very sweet to experience that.” (A mother, middle age)	5 (100%)	27 (62.8%)

Frequency (FG) = the frequency of a subtheme among focus group interviews (n = 5) of the positive healthy eating condition; Frequency (p) = the frequency of a subtheme among qualitative participants (n = 43) of the positive healthy eating condition.

Cognitive change toward healthy eating

Paying more attention to the intake of healthy food, particularly being more aware of sugar consumption, was a recurring theme in focus group discussions. The participants noted that they used to be impulsive in food selection, such as choosing sugary drinks and sugary snacks based on personal preference. After participating in the program, they became more cautious about what they ate and constantly reminded themselves about healthy eating.

Developing healthy eating habits

The focus group participants also indicated that they had developed healthy eating habits, which was a recurring theme in the discussion of health behavior change following participation in PHE. The key findings of this theme included reading the food label to check the sugar content, following a balanced diet as a key to good health, and using family support to maintain healthy eating practices.

Qualitative results on family quality of life

The focus group interviews showed that the PHE program offered an opportunity for families to partake in health-promotion behaviors together, thereby facilitating more frequent and enjoyable family interactions for family quality of life. The participants associated engagement in cooking and eating healthily together with family members to positive family outcomes. These included family bonding and positive affective experiences.

Family bonding

Participating in the PHE program enabled family members to connect with each other and improve their relationships. They perceived gathering in the kitchen and at the dining table as family activities that foster harmonious relationships, create a sense of togetherness, and facilitate communication. These activities helped family members create and intensify positive experiences together. The positive experiences extended from the PHE sessions to the participants’ daily routines.

Positive affective experiences

The participants experienced a sense of happiness and satisfaction when reminiscing about an HD experience with family members. They showed appreciation to family members for preparing a healthy meal and they savored the quality time they had during HD. The positive experiences were not only generated in the program sessions, but also from day-to-day interactions with family members. The positive emotions experienced during HD served as an incentive salience to repeating and maintaining health behavior within families.

Discussion

This study has first shown that a brief positive healthy eating intervention (PHE) was effective in increasing the intentions to change immediately after the core session, engagement in low-sugar dietary practices both individually and with family members at 3-month follow-up, and in reducing sugar consumption from sugar-sweetened beverages at 1-month and 3-month follow-up, with small effect sizes. Within-group improvements were also observed in PHE for low-sugar dietary practices with family members (T₃, T₄) and reduced sugar consumption from sugar-sweetened beverages (T₃, T₄). The control group showed within-group improvements in low-sugar dietary practices with family members (T₃) and reduced sugar consumption from sugar-sweetened beverages (T₄). Intentions to change mediated PHE’s effects on low-sugar dietary practices (T₃, T₄). Sensitivity analysis using complete-case data produced largely similar results, suggesting that the findings are robust. The qualitative results supported the quantitative results on intervention effectiveness and provided in-depth insights into the participants’ behavior change process, improved family bonding through healthy eating, and positive affective experiences during HD.

Although our small effect sizes are consistent with those found in other health behavior change interventions involving dietary change as shown by meta-analyses (Albarracín et al., 2018; Dusseldorp et al., 2014; Michie et al., 2009), the merits of our PHE program included simplicity, feasibility, acceptability, and reach at low cost. Our intervention effects were achieved in just two brief sessions (i.e. 3 hours in total) compared to other programs that required 12–72 weeks to produce similar effect sizes (Samdal et al., 2017). As PHE was run by non-health professionals after a 2.5-day training workshop, it can be easily disseminated by such training and empowerment of many people including volunteer workers for implementation in community settings. The feasibility and acceptability of PHE were demonstrated through successful implementation at a citywide level in the general population, which is rare in the literature where the interventions were typically restricted to a specific context (Albarracín et al., 2018) for a specific subgroup (Carrero et al., 2019). These qualities of PHE align with the principles of public health, which emphasizes the importance of implementing interventions that are cost-effective for reaching and benefitting a significant portion of the general population (Spoth et al., 2002). PHE therefore, offers a cost-effective solution to reducing the sugar intake of individuals and families, thereby potentially improving the cardiometabolic health at a large scale in the community (Huang et al., 2023).

Our findings support the upward spiral theory of lifestyle change (Van Cappellen et al., 2018), which proposes that health behaviors are likely to be repeated and maintained when they are enjoyable and pleasant. The participants associated positive affective experiences with HD by utilizing the positive psychological constructs of joy, gratitude, and savoring, whereby non-conscious motives were created and strengthened for subsequent engagement in HD. Consistent with this explanation, correlational studies revealed that positive psychological constructs of positive affect, hope, and optimism were prospectively associated with reduced risk of cardiovascular disease, diabetes, and mortality (Amonoo et al., 2021; Schiavon et al., 2020). The researchers explained that engagement in healthy behaviors, such as physical activity and healthy diet, are viable mechanisms by which positive psychological constructs could lead to improved health. Conversely, correlational studies that showed healthy food consumption (e.g. fruits and vegetables) predicted happiness, life satisfaction, and well-being (Holder, 2019) provided support for a positive feedback loop. That is, being happy and feeling well are associated with increased engagement in health behaviors, and these lifestyle choices are in turn associated with enhanced well-being and health (Kesavayuth et al., 2022), thus further strengthening the motivation to repeat those behaviors and forming an upward spiral of lifestyle change. Since the quantitative results from our trial only showed the effects of joy, gratitude, and savoring in our intervention programs, namely PPA and PHE (Ho et al., 2020b), further research is needed to identify other positive psychological constructs suitable for integration with various health behaviors and the use of positive feedback loop to promote lifestyle change.

Some of the intended intervention outcomes were not supported. PHE participants only benefited in low-sugar dietary practices individually and with family members at 3 months but not at 1 month after the intervention. A possible explanation is that the participants only received a core session at 1-month follow-up assessment, suggesting that one session was not sufficient to produce the intended behavior change. The booster session aimed to consolidate the knowledge and skills from the core session, allowing participants to share their experiences and barriers that they had encountered in engaging healthy eating, and to further establish health behavior change. Therefore, our findings suggest that a minimum of two sessions, totaling 3 hours, are needed for a brief life style intervention to produce desirable changes in behavior.

Another reason could be that the participants needed more time to contemplate and prepare themselves for adopting a different lifestyle. Indeed, health behavior change theories generally propose different stages of change for a new behavior to be adopted and maintained (Schwarzer, 2008). In particular, the transtheoretical model posits that people could enter the contemplation or preparation stage after taking part in the first session of PHE, which can take up to 6 months before they exhibit new healthy behaviors. In line with this perspective, our findings suggest that 3 months are needed for people to think about whether to initiate the change process and to mentally, physically, and socially prepare for a different lifestyle before they embark on a healthier and happier journey with family members.

As an exploratory question, we investigated whether intentions to change could explain the intervention’s effects on low-sugar dietary behaviors, for which we showed that intentions mediated PHE’s effects on low-sugar dietary practices in general, but not reductions sugar-sweetened beverages specifically. The specificity of the outcome measures might have produced these differences in findings. Since both intentions and engagement referred to low-sugar dietary practices, the intentions-behavior link is more explicit and relevant. Participants may have various options to reduce sugar intake in their meals, so reduction in sugar-sweetened beverages may not represent the diet of those who had the intentions to eat healthily. This is because participants were given the autonomy to decide and prepare their own healthy meals rather than a strict healthy diet plan to follow. Nevertheless, recent research suggests that a flexible or rigid diet strategy can be equally effective (Conlin et al., 2021).

Our study had some limitations. First, cRCT was adopted in which randomization was conducted at a cluster level instead of an individual level to avoid contamination within the same family and recruiting site. Nevertheless, the intervention and control groups were comparable at baseline and the analysis was adjusted for baseline factors. Second, voluntary participation with informed consent might have introduced self-selection bias because the program might have attracted individuals who were readier for changes. However, the diversity of the settings and participants enhanced the generalizability of our results. Third, as this was a community-based project, more service recipients joined the programs than the reported number of participants who fulfilled the eligibility criteria and provided data for the study. This was inevitable because the social service units and schools were obliged to provide services to their clients regardless of the study requirements. Fourth, low-sugar dietary practices and intake of sugar-sweetened beverages were self-reported, so the results might be susceptible to reporting bias. This might explain the significant increase for the control group on engagement in low-sugar dietary practices with family members at T₃ and reduction in sugar consumption from sugar-sweetened beverages at T₄. Nevertheless, cRCT was adopted to assess between-group differences empirically while accounting for self-report bias and placebo effects by balancing between treatment and control (Spieth et al., 2016). Finally, although the intervention programs were implemented in community settings, the timing and location might influence intervention effectiveness. As the study involved recruitment and implementation in community centers, social service centers, and primary and secondary schools, the participants were likely to be familiar with the intervention environment. This may limit the generalizability of the results to other settings or places with a different community infrastructure.

The PHE intervention employed a community-based strategy, working closely with local community partners, to enhance healthy eating practices. The results, both quantitative and qualitative, demonstrate that a lifestyle intervention integrating positive psychological constructs with healthy eating is effective for promoting low-sugar consumption in the community. This approach emphasizes the importance of a healthy lifestyle, which is often overlooked in psychosocial interventions. This integration aligns with the urgent need to address the global non-communicable disease pandemic caused by unhealthy eating habits. The innovative PHE intervention offers a feasible, acceptable, and cost-effective approach that can be implemented in the community by non-health professionals who serve diverse groups of community dwellers. Other cities and communities are encouraged to adopt this intervention model through building a taskforce of social and health care professionals and lining up with community stakeholders to design and deliver effective interventions to create public health impact. Since the straightforward and practical aspects of PHE can be easily incorporated into a daily routine, individuals and families can apply this intervention method by using cooking and dining activities to improve health, happiness, and harmony at home.

Supplemental Material

sj-docx-1-hpq-10.1177_13591053231225934 – Supplemental material for A cluster randomized controlled trial of a brief positive healthy eating intervention

Supplemental material, sj-docx-1-hpq-10.1177_13591053231225934 for A cluster randomized controlled trial of a brief positive healthy eating intervention by Henry CY Ho, Agnes Y Lai, Moses Wai-keung Mui, Alice Wan, Carol Wing-see Yew and Tai Hing Lam in Journal of Health Psychology

Footnotes

Acknowledgements

We thank our community collaborators and research participants for their coordination, implementation, and participation in the community programs. We are also grateful to our research team (Ms. Grace Lau, Ms. Maggie Chan, Ms. Jamie Chan, Ms. Sally Leung, Ms. Michelle Suen, Mr. Isaac Yau, and Ms. Jillian Zhou) for their important contributions. We thank Dr. Danice Ng for the development of the sugar-sweetened beverage intake measure.

Author contributions

Agnes Y. Lai is now at the Hong Kong Metropolitan University, Hong Kong. Moses Wai-keung Mui is now at The ExtraCare Charitable Trust, United Kingdom. Alice Wan is now at Aberdeen Kai-Fong Welfare Association Social Service Centre, Hong Kong. Carol Wing-see Yew is now at The Government of the Hong Kong SAR, Hong Kong.

Data sharing statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was a part of the project entitled “FAMILY: A Jockey Club Initiative for a Harmonious Society,” which was funded by The Hong Kong Jockey Club Charities Trust. The funder had no role in study design, data collection, data analysis and interpretation, preparation of the manuscript, or decision to publish.

Ethics approval

The Institutional Review Board of the University of Hong Kong/Hospital Authority Hong Kong West Cluster granted ethics approval (UW 15-083). The study was preregistered in ClinicalTrials.gov (NCT02563613).

Informed consent

Written informed consent was obtained prior to participation.

ORCID iD

Henry CY Ho

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