An interventional study of No Nudge (control) and JIT Visibility Only Nudge in Behavior: Healthy Food Choice, sponsored by Tilburg University. Completed at 1 site in Netherlands. Open to participants aged 18 Years and older, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-09-25.
Sponsored by Tilburg University · Not applicable, Interventional, and Prevention
This study used a randomized five-condition experiment in a mock online supermarket to investigate whether just-in-time (JIT) food-swap recommendations can improve the healthiness of food choices and whether different types of justification: visibility-only, descriptive/normative language (DNL), social norms, and hedonic enhancement, affect recommendation acceptance and food choice healthiness. The study also examined the psychological mechanisms underlying these effects, focusing on ethe ease of identifying healthy options (EIHO) as a facilitating mechanism and psychological reactance as a potential barrier, and explored whether effects varied by socioeconomic position, food choice motives, and decision-making styles. Ultimately, the study aimed to identify personalization approaches that can make JIT food-swap recommendations effective across the socioeconomic gradient.
This study employed a between-subjects design with one factor (JIT justification type) and five levels/conditions: no recommendation; JIT visibility-only (recommendation without justification); DNL; social norm; and hedonic enhancement. Acceptance rate and healthiness of food choices were the primary outcome variables. Participants were randomly assigned to one of the conditions and then completed a hypothetical grocery-shopping task using MAND, a mock supermarket app developed by NAKKO. Psychological reactance and ease of identifying healthier options (EIHO) were included as mediating variables. General decision-making style (GDMS), food choice motive (FCM), education level, and subjective socioeconomic position were included as moderating variables. This study was approved by the Ethical Review Board of the Tilburg School of Humanities and Digital Sciences (Identification code: REDC2023.34abc).
The study was conceptually divided into two models for theoretical clarity. Model 1 (The JIT Presence Mediation Model) focused on the effects of the JIT visibility-only recommendation (versus no JIT) on healthiness of food choices. Model 2 (JIT Justification Type Moderation Model) focused on the effects of JIT justification types (DNL, hedonic enhancement, social norms versus JIT visibility-only recommendation) on acceptance rate. Our hypotheses are visualized in the conceptual models 1 and model 2 and were preregistered at the Open Science Framework (osf.io/y29ha). The hypotheses and models differ from the original preregistration only in their numbering, which was revised to clarify and separate the models, and in minor rewording for clarity.
Aims:
The study aimed to examine the effects of different Just-In-Time food-swap recommendations on healthiness of food choices (model 1) and on acceptance rate (model 2). The study also explored the facilitating (ease of identifying healthier options) and hindering (psychological reactance) underlying mechanisms, and whether they differed by SEP, domain-general (GDMS) and food-specific (FCM) individual characteristics. Lastly, the study aimed to contribute to identifying personalization approaches that could make JIT food swap recommendations effective across the socioeconomic gradient
Exclusion Criteria:
Participants are not presented with a pop-up showing a suggested alternative. After making their selection, they are immediately routed back to the start screen, where they can click on the next product category.
Other: No Nudge (control)
An alternative product (image, product name, and price) is suggested in the pop-up, accompanied by a header that reads "Alternative"
Other: JIT Visibility Only Nudge
This nudge is the same as the JIT visibility only nudge condition, but with an additional text providing health information on the alternative compared to the original choice (e.g., "This product contains less salt").
Other: Descriptive Nutritional Labelling Nudge.
This nudge is the same as the JIT visibility only nudge condition, but with an additional descriptive text (e.g., "Delicious and refreshing"). Furthermore, the product image is replaced with an enhanced version that highlights the product's taste and visual appeal.
Other: Hedonic Enhancement Nudge
This nudge is the same as the JIT visibility only nudge condition, but with an additional descriptive prompt (e.g., "4 out of 5 people chose this") and a visual representation.
Other: Social Norm Nudge
No Nudge. Participants are not presented with a pop-up showing a suggested alternative. After making their selection, they are immediately routed back to the start screen, where they can click on the next product category.
An alternative product (image, product name, and price) is suggested in the pop-up, accompanied by a header that reads "Alternative".
This nudge is the same as the JIT visibility only nudge condition, but with an additional text providing health information on the alternative compared to the original choice (e.g., "This product contains less salt").
This nudge is the same as the JIT visibility only nudge condition, but with an additional descriptive text (e.g., "Delicious and refreshing"). Furthermore, the product image is replaced with an enhanced version that highlights the product's taste and visual appeal.
This nudge is the same as the JIT visibility only nudge condition, but with an additional descriptive prompt (e.g., "4 out of 5 people chose this") and a visual representation.
Healthiness of Food Choices (basket healthiness)
The healthiness of each participant's final basket (i.e., after the possibility to swap before final checkout) was measured by using the FNS score of each product and calculating the average score of the six products they selected for experimental product categories. The FNS score ranges from -15 to +40. A smaller average FNS score means healthier food choices.
Time frame: During the retail application session
Acceptance rate
Recommendation acceptance rate was measured as the proportion of recommendations accepted during experimental trials, calculated as the number of accepted recommendations divided by the total number of recommendations presented (ranging from 3 to 6).
Time frame: During the retail application session
Ease of Identifying Healthier Options (EIHO)
EIHO was assessed by one question asking participants how easy it was to identify healthy products during the grocery shopping task. Responses were recorded on a 7-point Likert scale, ranging from 1 = "Not easy at all" to 7 = "Very easy", with higher scores indicating greater ease in identifying the healthier options \[1\].
Time frame: immediately after the intervention
Psychological Reactance
Psychological reactance was measured using four items assessing anger (e.g., "This app made me feel irritated") and four items assessing perceived threat to freedom (e.g., "I felt like my choices were being restricted"). Participants responded on a 5-point Likert scale, ranging from 1 = "Strongly disagree" to 5 = "Strongly agree." Scores were calculated by averaging responses across items, with higher scores indicating greater psychological reactance (α = .87)
Time frame: immediately after the intervention
Choice Satisfaction
After completing the shopping task, participants rated their satisfaction with their selected products on a 0-100 scale, with anchors ranging from 0 = "Not satisfied at all" to 100 = "Very satisfied."
Time frame: immediately after the intervention
Perceived Personalization
Perceived personalization was assessed using two statement items, with a seven-point Likert scale (1 = "Strongly Disagree"; 7 = "Strongly Agree"): e.g., "The MAND app was aimed at me as a unique individual".
Time frame: immediately after the intervention
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Plan to share: No — Data will be shared via the organisation's data repository - Dataverse
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Tilburg University