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Promoting the adoption of public goods that are not yet widely accepted is particularly challenging. This is because most tools for increasing cooperation—such as reputation concerns 1 and information about social norms 2 —are typically effective only for behaviours that are commonly practiced, or at least generally agreed upon as being desirable. Here we examine how advocates can successfully promote non-normative (that is, rare or unpopular) public goods. We do so by applying the cultural evolutionary theory of credibility-enhancing displays 3 , which argues that beliefs are spread more effectively by actions than by words alone—because actions provide information about the actor’s true beliefs. Based on this logic, people who themselves engage in a given behaviour will be more effective advocates for that behaviour than people who merely extol its virtues—specifically because engaging in a behaviour credibly signals a belief in its value. As predicted, a field study of a programme that promotes residential solar panel installation in 58 towns in the United States—comprising 1.4 million residents in total—found that community organizers who themselves installed through the programme recruited 62.8% more residents to install solar panels than community organizers who did not. This effect was replicated in three pre-registered randomized survey experiments (total n  = 1,805). These experiments also support the theoretical prediction that this effect is specifically driven by subjects’ beliefs about what the community organizer believes about solar panels (that is, second-order beliefs), and demonstrate generalizability to four other highly non-normative behaviours. Our findings shed light on how to spread non-normative prosocial behaviours, offer an empirical demonstration of credibility-enhancing displays and have substantial implications for practitioners and policy-makers. A field study and three experiments demonstrate that people who engage in rare (non-normative) prosocial behaviours will be more effective advocates for those behaviours than people who merely praise the virtues of these prosocial behaviours.

Pictorial warnings on tobacco products are promising for motivating behavior change, but few studies have examined pictorial warnings for sugary drinks, especially in naturalistic environments. This study aimed to examine the impact of pictorial warnings on parents' purchases of sugary drinks for their children in a naturalistic store laboratory. Parents of children ages 2 to 12 (n = 325, 25% identifying as Black, 20% Hispanic) completed a shopping task in a naturalistic store laboratory in North Carolina. Participants were randomly assigned to a pictorial warnings arm (sugary drinks displayed pictorial health warnings about type 2 diabetes and heart damage) or a control arm (sugary drinks displayed a barcode label). Parents selected 1 beverage and 1 snack for their child, as well as 1 household good; one of these items was selected for them to purchase and take home. The primary outcome was whether parents purchased a sugary drink for their child. Secondary outcomes included reactions to the trial labels, attitudes toward sugary drinks, and intentions to serve their child sugary drinks. Pictorial warnings led to a 17-percentage point reduction in purchases of sugary drinks (95% CI for reduction: 7% to 27%), with 45% of parents in the control arm buying a sugary drink for their child compared to 28% in the pictorial warning arm (p = 0.002). The impact of pictorial warnings on purchases did not differ by any of the 13 participant characteristics examined (e.g., race/ethnicity, income, education, and age of child). Pictorial warnings also led to lower calories (kcal), purchased from sugary drinks (82 kcal in the control arm versus 52 kcal in the pictorial warnings arm, p = 0.003). Moreover, pictorial warnings led to lower intentions to serve sugary drinks to their child, feeling more in control of healthy eating decisions, greater thinking about the harms of sugary drinks, stronger negative emotional reactions, greater anticipated social interactions, lower perceived healthfulness of sugary drinks for their child, and greater injunctive norms to limit sugary drinks for their child (all p < 0.05). There was no evidence of difference between trial arms on noticing of the labels, appeal of sugary drinks, perceived amount of added sugar in sugary drinks, risk perceptions, or perceived tastiness of sugary drinks (all p > 0.05). Pictorial warnings reduced parents' purchases of sugary drinks for their children in this naturalistic trial. Warnings on sugary drinks are a promising policy approach to reduce sugary drink purchasing in the US. The trial design, measures, power calculation, and analytic plan were registered before data collection at www.clinicaltrials.gov NCT04223687.

Background Evidence on what strategies - or combination of strategies - are most effective and equitable in promoting healthier diets is needed. This study examined the efficacy of nudging and pricing strategies on increasing healthy food purchases and the potential differential effect by socio-economic position (SEP) among Dutch adults in a virtual supermarket. Methods A randomized study design was conducted within a virtual supermarket (SN VirtuMart). Participants were exposed to five within-subject study conditions (control, nudging, pricing, price salience and price salience with nudging) and randomized to one of three between-subject study arms (a 25% price increase on unhealthy products, a 25% discount on healthy products, or a 25% price increase and discount). In total, 455 participants of low and high SEP (using either education or income as proxy) were randomized to conduct their weekly shopping in a virtual supermarket for five consecutive weeks. The primary outcome included the percentage of healthy purchases. Data were analyzed using linear mixed models. Results In total, 346 (76%) adults completed all five shops within the SN VirtuMart. Median age was 32.5, 49.2% had high education and 32.8% had high income. Out of the 12 conditions, four conditions were statistically significantly different from the control condition. Nudging and non-salient pricing strategies alone did not statistically significantly increase healthy food purchases, whereas a combination of salient price increases and discounts led to an increase in the percentage of healthy food purchases (B 4.5, 95%CI 2.6; 6.4). Combining salient pricing and nudging strategies led to increases in the percentage of healthy products in all three pricing arms, with largest effects found in the combined price increase and discount arm (B = 4.0, 95%CI = 2.0; 6.0). Effects were not modified by SEP. Conclusions Combining health-related price increases and discounts and combining these salient pricing strategies with nudges in a supermarket setting seems to stimulate healthy food purchases for both low and high SEP populations. However, further research in real-world settings is needed. Trial registration This randomized trial ( NTR7293 ) was registered in the Dutch trial registry ( www.trialregister.nl ).

The current format of summary of findings (SoFs) tables for presenting effect estimates and associated quality of evidence improve understanding and assist users finding key information in systematic reviews. Users of SoF tables have demanded alternative formats to express findings from systematic reviews. We conducted a randomized controlled trial among systematic review users to compare the relative merits of a new format with the current formats of SoF tables regarding understanding, accessibility of information, satisfaction, and preference. Our primary goal was to show that the new format is not inferior to the current format. Of 390 potentially eligible subjects, 290 were randomized. Of seven items testing understanding, three showed similar results, two showed small differences favoring the new format, and two (understanding risk difference and quality of the evidence associated with a treatment effect) showed large differences favoring the new format [63% (95% confidence interval {CI}: 55, 71) and 62% (95% CI: 52, 71) more correct answers, respectively]. Respondents rated information in the alternative format as more accessible overall and preferred the new format over the current format. While providing at least similar levels of understanding for some items and increased understanding for others, users prefer the new format of SoF tables.

Background Reducing the environmental impact of foods consumed is important for meeting climate goals. We aimed to conduct a randomised controlled trial to test whether ecolabels reduce the environmental impact of food selected in worksite cafeterias, alone or in combination with increased availability of more sustainable meal options. Methods Worksite cafeterias ( n  = 96) were randomised to one of three study groups, with 54 included for final analysis. One group was intended to increase the availability of meat-free options, but no change was implemented. Therefore, this group was treated as part of the control, creating two groups: (1) control (no ecolabels) ( n  = 35), and (2) ecolabels ( n  = 19). Regression analysis assessed the primary outcome of total environmental impact of hot meals sold over a 6-week period. Secondary outcome analyses explored the individual environmental indicators that composed the total environmental impact score (i.e., greenhouse gas emissions, biodiversity loss, eutrophication, and water scarcity). The mean weekly environmental impact scores of hot meal options over the full 12-week trial period were assessed using hierarchical mixed effects models. Results There was no significant effect of the intervention on the environmental impact scores of meals sold (mean difference between control and intervention sites: -1.4%, 95%CI: -33.6%, + 30.8%). There was no evidence of an effect in mean weekly environmental impact score (-5.4%, 95%CI: -12.6%, + 2.5%), nor in any of the four individual environmental indicators (greenhouse gas emissions: -3.6%, 95%CI: -30.7%, 34.3%; biodiversity loss: 2.0%, 95%CI: -25.8%, 40.2%; eutrophication: -2.4%, 95%CI: -29.3%, 34.7%; water scarcity: -0.4%, 95%CI: -28.7%, 39.1%). Conclusions Ecolabels may not be an effective tool to shift consumer behaviour in worksite cafeterias towards meals with lower environmental impact. Trial registration The study was pre-registered prospectively on ISRCTN ( https://www.isrctn.com/ISRCTN10268258 ; 06/01/2022).

Background Front-of-package labelling is a cost-effective strategy to help consumers make healthier choices and informed food purchases. The effect of labels is mediated by consumer understanding and acceptability of the label. We compared the acceptability and understanding of labels used in Latin-America among low- and middle-income Mexican adults. Methods Participants ( n  = 2105) were randomly assigned to one of three labels: Mexican Guideline Daily Allowances (GDA), Ecuador’s Multiple Traffic Lights (MTL), or Chile’s Warning Labels (WL) in red. Label acceptability was evaluated through items regarding likeability, attractiveness and perceived cognitive workload. Objective understanding was evaluated by asking participants to select the product with the lowest nutritional quality among three products. We measured the time participants took to choose the product. Differences in label acceptability, understanding and time required to choose a product across labels were tested. Results Compared to the GDA, a higher proportion of participants liked the MTL and WL, considered them attractive, and with a lower perceived cognitive workload ( p  < 0.05). Participants had 4.00 (2.86–5.59) times the odds of correctly identifying the product with the lowest nutritional quality when using the MTL label and 4.52 (3.24–6.29) times the odds when using the WL, in comparison to the GDA. Time required to choose the product was lower for the MTL (Median: 11.25 s; IQR = 8.00–16.09) and the WL (Median = 11.94 s, IQR = 8.56–16.52) compared to the GDA (Median: 15.31 s; IQR = 10.81–20.21; p  < 0.05). No differences were observed between the MTL and the WL. Conclusions GDA had the lowest acceptability and understanding among the labels tested. The MTL and the WL were more accepted and understood, and allowed low- and middle-income consumers to make nutrition-quality related decisions more quickly. WL or MTL may foster healthier food choices in the most vulnerable groups in Mexico compared to the current labelling format.

Background Interventions to reduce the saturated fat (SFA) content of food purchases may help reduce SFA consumption and lower cardiovascular risk. This factorial RCT aimed to examine the effect of altering the default order of foods and being offered a swap on the SFA content of food selected during an online shopping experiment. Methods UK adults who were the primary grocery shoppers for their household were recruited online and invited to select items in a custom-made experimental online supermarket using a 10-item shopping list. Participants were randomly allocated to one of four groups (i) to see products within a category ranked in ascending order of SFA content, (ii) receive an offer to swap to a product with less SFA, (iii) a combination of both interventions, or (iv) no intervention. The primary outcome was the difference in percentage energy from SFA in the shopping basket between any of the four groups. The outcome assessors and statistician were blinded to intervention allocation. Results Between March and July 2018, 1240 participants were evenly randomised and 1088 who completed the task were analysed (88%). Participants were 65% female and aged 38y (SD 12). Compared with no intervention ( n  = 275) where the percentage energy from SFA was 25.7% (SD 5.6%), altering the order of foods ( n  = 261) reduced SFA by [mean difference (95%CI)] -5.0% (− 6.3 to − 3.6) and offering swaps ( n  = 279) by − 2.0% (− 3.3 to − 0.6). The combined intervention ( n  = 273) was significantly more effective than swaps alone (− 3.4% (− 4.7 to − 2.1)) but not different than altering the order alone (− 0.4% (− 1.8 to 0.9)), p  = 0.04 for interaction. Conclusions Altering the default order to show foods in ascending order of SFA and offering a swap with lower SFA reduced percentage energy from SFA in an experimental online supermarket. Environmental-level interventions, such as altering the default order, may be a more promising way to improve food purchasing than individual-level ones, such as offering swaps. Trial registration ISRCTN13729526 https://doi.org/10.1186/ISRCTN13729526 26th February 2018.

Background Frequent out-of-home food sector (OOHFS) use is associated with poor dietary intake and obesity. There are limited real-world studies on pricing interventions to encourage healthy eating in the OOHFS. We performed a pilot study to collect preliminary trial data on the potential impact of a price reduction intervention on healthier menu items on purchasing and consumption of kilocalories (kcal) in a full-serviced restaurant among people from both lower and higher socioeconomic position (SEP). Methods The main trial design was a pre vs. post price reduction comparison (within-subjects), where participants (adults aged ≥ 18 years) received a control menu with standard pricing at visit 1 and a menu with price manipulations (30% reduction for healthy items) at visit 2. A sub-study was conducted with a comparison sample to estimate potential pre-post changes to outcome variables in the absence of a pricing intervention. Linear mixed models assessed pre-post changes in kcal purchased and kcal consumed. Results In total, 114 participants were recruited; 92 were randomised to the main study and 22 to the comparison sub-study. Of those participating in the main study, 78 completed and 14 were lost to follow-up. There were no participants lost to follow-up in the comparison study. Of the completers, 46 participants were considered higher SEP (i.e. bachelor’s degree or higher) and 32 participants were lower SEP (i.e. some college or associate degree or lower). Kcal purchased and consumed decreased from visit 1 to visit 2; however, this reduction was only statistically significant for total kcal consumed (regression coefficient: -98.0 (95% CI -181.9, -14.2), p  = 0.02). There were no notable intervention effect differences between higher and lower SEP participants, but we were under-powered to formally test for SEP differences. In the comparison study, kcal purchased and consumed was also lower at visit 2 compared to visit 1, although this should be interpreted with caution due to the small sample size. Conclusion A price reduction intervention on lower energy menu items is potentially effective in encouraging healthier eating in a restaurant setting. Larger studies with inclusion of a control group (e.g., randomised controlled trials) are now needed to confirm intervention effects and whether they are equitable across different socioeconomic groups.

Several studies have identified Front-of-Pack Nutrition Labels (FoPLs) as a promising strategy to improve the nutritional quality of consumers’ food choices and encourage manufacturers to offer healthier products. This study aims to fill the evidence gap regarding the most effective FoPL among the Portuguese population. In total, 1059 Portuguese participants were recruited through a web panel provider and asked to declare their intended food choices and to rank three sets of products (pizza, cakes and breakfast cereals) according to their nutritional quality, first in the absence of any labelling, and then with a FoPL displayed on-pack (five FoPLs tested). Finally, participants were asked to answer nine statements related to perceptions of FoPLs. Results showed that participants improved their food choices, depending on the FoPL and the food category. All FoPLs led to a higher percentage of correct responses on the ranking task compared to the no label condition. The Nutri-Score was among the FoPLs producing the greatest improvement across all food categories compared to the reference intakes (OR = 6.45 [4.43–9.39], p-value < 0.0001) and facilitating the highest percentage to correctly rank products according to nutritional quality. This study suggests that, among the available options, Nutri-Score is the most efficient FoPL to inform Portuguese consumers of the nutritional quality of foods and help them identify healthier options in mock purchasing situations.