The Impact of Price Promotions on Purchases of Confectionery and Snacks: a Randomised Controlled Trial in an Experimental Online Supermarket Study

BACKGROUND AND RATIONALE

As a nation people eat more energy, free sugars, saturated fat and salt than recommended for good health. These nutrients contribute to the burden of major chronic diseases, including cardiovascular disease and diabetes, principally through effects on blood cholesterol, blood pressure, insulin sensitivity or body weight. In addition, persistent inequalities in dietary intake underpin inequalities in long-term health outcomes. Despite decades of health promotion, dietary change is slow. Growing evidence suggests people need more than general knowledge about the healthfulness of foods to change behaviour.

Food purchasing is a key antecedent of food consumption and interventions to change food purchasing habits may be more impactful than interventions intended to change consumption at the moment of eating. Supermarkets account for the majority of the weekly expenditure on food and drinks, estimated to be around 87% of all UK retail grocery sales. Impactful, scalable and sustainable approaches within supermarkets are particularly needed in order to shift population-level intakes to be closer to the recommendations for calories, sugar, salt and saturated fat.

Previous systematic reviews of supermarket interventions have identified effective strategies to support dietary change. Evidence is generally stronger for economic (e.g. price interventions or price promotions), positioning and availability interventions. However, many of the interventions described in the literature are multi-component, and there is a challenge in attributing their effectiveness to any single strategy. In the 2020 Obesity Plan, the government in England laid out plans to introduce legislation to restrict the promotion of high fat salt sugar (HFSS) foods, by restricting volume promotions such as 'Buy One Get One Free'. This is based on observational evidence of purchasing habits. Specific evidence of the impact of removing promotions is of interest to policymakers and could help in shaping effective but proportionate policies.

Online supermarkets offer unique opportunities to deliver and support complex nutrition interventions that can often be tested and scaled up more rapidly and feasibly using digital technology than in-store interventions. There is some evidence that baseline purchases made online tend to be healthier than purchases in physical stores, but less is known about the effectiveness of interventions delivered online to change behaviour.