Background One third of all greenhouse gas emissions come from the food system. Transitioning towards more sustainable and healthy diets can serve co-benefits for environmental and human health. Digital behaviour change interventions are increasingly seen as scalable, low-cost, and equitable, given the ubiquity of internet access and smartphone ownership regardless of socioeconomic status. Despite this, there is poor consensus around their effectiveness outside of patient populations. Therefore, this systematic review aimed to investigate the effectiveness of mobile app-based interventions in promoting sustainable and healthy diets in non-clinical adult populations.

Methods Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, seven electronic databases (MEDLINE, EMBASE, PsycINFO, CINAHL, Global Health, GreenFILE, and Web of Science) were searched for articles published up to 7 February 2023 and two trial registries (Cochrane Trials and Clinicaltrials.gov) were searched on 10 February 2023. Empirical studies were eligible for inclusion if they quantitatively measured plant-based, animal-based, local, seasonal, and/or discretionary food consumption, the intervention incorporated a smartphone application, and targeted adults residing in a high-income country defined by the World Bank (2021). A conceptual model summarising the factors contributing to dietary consumption and possible intervention functions was developed using the Determinants of Nutrition and Eating (DONE) framework and the Behaviour Change Wheel, respectively.

Results Screening and analysis are ongoing for the 5261 total records. Preliminary results indicate intervention functions vary between high-agency apps that require individuals to download and adhere to a standalone app and lower-agency apps that utilise an existing app as an interface, for example supermarket delivery apps. While high-agency apps commonly implement education and training, lower-agency apps implement environmental restructuring and restrictions. We will measure effectiveness across the five food-based outcome categories, and differences according to the intervention functions, behaviour change techniques, target determinants, and populations. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) criteria will be used to assess the certainty of evidence.

Conclusion Our findings will highlight key intervention functions and effect modifiers of interest to app developers, researchers, and policymakers in the design, implementation, funding, and evaluation of apps promoting sustainable and healthy diets. The results will directly inform app prototype development to be tested in a discrete choice experiment and complementary qualitative study, to understand how people integrate apps into habitual social practices of shopping, preparation, and eating. Moreover, our data synthesis and conceptual framework methodology will provide actionable insights for future reviews in the area.