Evaluation of Combinations of Nudging, Pricing, and Labeling Strategies to Improve Diet Quality: A Virtual Grocery Store Experiment Employing a Multiphase Optimization Strategy.

Background: Several intervention strategies have been shown to improve diet quality. However, there is limited evidence on the increase in effectiveness that may be achieved through select combinations of these strategies.

Purpose: This study aimed to identify an effective multicomponent intervention to improve diet quality of a grocery basket by applying a Multiphase Optimization Strategy framework and testing various combinations of four promising strategies using a fully functional web-based grocery store: (i) front-of-pack food labels and real-time feedback of the healthiness of the shoppers' grocery basket, (ii) a tax, (iii) ordering products by a nutritional quality score, and (iv) healthier substitute offers.

Methods: We conducted a hypothetical shopping study (N = 756) with a randomized full factorial design (16 conditions) to estimate main and interaction effects of the four interventions.

Results: The "food labels & real-time feedback" and "ordering" strategies had significantly positive main effects on overall diet quality of the shopping basket (both at p < .001). We found no effects on diet quality for the "tax" and "healthier substitute offers." None of the two-way interaction effects for different strategies on overall diet quality and nutrients were significant.

Conclusions: Having "food labels & real-time feedback" and "ordering" simultaneously seemed to be more effective at improving diet quality, compared to having only one of these interventions. These results suggest that a combination of food labels with real-time feedback and ordering interventions can be part of a promising multicomponent strategy to improve diet quality in online shopping platforms.

Trial registration: ClinicalTrials.gov NCT04632212.