Abstract 53: Real-Life Effects of Nudging and Pricing Strategies in the Supermarket to Promote Healthy Diets and Cardiometabolic Health: The Supreme Nudge Parallel Cluster-Randomized Controlled Trial
Authors: Mackenbach Joreintje D , Stuber Josine M , Middel Cédric N , Lakerveld Jeroen , Beulens Joline W 
Published: March 2023

Introduction:
Unhealthy food intake is a major risk factor for cardiometabolic diseases. Individual-level efforts to promote heathy diets (e.g., nutrition education) have limited effect on the long term. Designing the choice context in such a way that it facilitates healthy food choices may contribute to sustainable prevention of cardiometabolic diseases. We evaluated the real-life effects of nudging and pricing strategies in supermarkets.

Hypothesis:
Exposure to store-level nudging and pricing will improve dietary guideline adherence, healthy food purchasing and customer satisfaction, and reduce cardiometabolic risk among Dutch adults after 12 months compared to no intervention.

Methods:
In this parallel cluster-randomized controlled trial, we randomized 12 Dutch supermarkets in socially disadvantaged neighborhoods to a control (n=6 supermarkets) or intervention group (n=6). Intervention supermarkets received healthy food nudges (across 13 food groups on circa 9% of supermarket products) and pricing strategies (price decreases on healthy products and increases on unhealthy products; on circa 3% of products). Eligible participants were aged 30-80 years and regular shoppers at participating supermarkets. The primary outcome was dietary guideline adherence measured via a validated index score (scale 0-150), at baseline and after 3, 6 and 12 months. Secondary outcomes included the percentage of healthy food purchases, parameters of cardiometabolic health (HbA1c (mmol/L), lipid profile (mmol/L), and waist circumference (cm)), and supermarket customer satisfaction (very unsatisfied (1) to very satisfied (7)). Implementation fidelity was regularly monitored (no implementation (1) to optimal implementation (5)).

Results:
Of the 361 participants included (162 intervention, 199 control), 73% were female, 42% were highly educated and the average age (sd) was 58 (11) years. Linear mixed models showed no effectiveness of the intervention compared to control on dietary guideline adherence (β -1.1, 95%CI: -3.8; 1.7), the total percentage of healthy purchases (β 0.4, 95%CI: -3.0; 3.7), HbA1c (β 0.6, 95%CI: -0.1; 1.3), lipid profile (LDL β -0.0, 95%CI: -0.2; 0.1, HDL β -0.0, 95%CI: -0.1; 0.0), and waist circumference (females β 0.7 (95%CI: -0.8; 2.2), males β 0.5, 95%CI: -2.4; 3.5) over the 12-month intervention period. Participants in the intervention clusters scored 0.3 points (95%CI: 0.1; 0.5) higher on overall customer satisfaction, compared to control clusters. Median implementation fidelity over time was 3.6 (range 2.9-4.1).

Conclusions:
Nudging and pricing strategies implemented in a real-life purchasing setting were not effective in promoting healthier diets and purchasing patterns nor in improving cardiometabolic health on an individual level. Sub-optimal intervention exposure due to practical implementation barriers may have contributed to these null results.