Offering within-category food swaps to reduce energy density of food purchases: a study using an experimental online supermarket.

Suzanna E Forwood,Susan A Jebb,Amy L Ahern,Theresa M Marteau

doi:10.1186/s12966-015-0241-1

Abstract

BackgroundSwaps are often used to encourage healthier food choices, but there is little evidence of their effectiveness. The current study assessed the impact of offering swaps on groceries purchased within a bespoke online supermarket; specifically the objective was to measure the impact on energy density (ED) of food purchases following the offer of lower ED alternatives (a) at point of selection or at checkout, and (b) with or without explicit consent to receive swap prompts.MethodParticipants were asked to complete a 12-item shopping task within an online shopping platform, developed for studying food purchasing. 1610 adults were randomly assigned to a no swap control condition or to one of four interventions: consented swaps at selection; consented swaps at checkout; imposed swaps at selection; or imposed swaps at checkout. Each swap presented two lower ED options from the same category as the participant’s chosen food. Swap acceptance rate and purchased food ED were the primary outcomes.ResultsOf the mean 12.36 (SD 1.26) foods purchased, intervention participants were offered a mean of 4.1 (SD 1.68) swaps, with the potential to reduce the ED of purchased food (effect (95 % CI): −83 kJ/100 g (−110 – -56), p = <0.0001). A median of one swap (IQR 0 to 2) was accepted, not significantly reducing the purchased food ED (effect (95 % CI): −24 kJ/100 g (4 – -52), p = 0.094). More swaps were accepted when offered at selection than at checkout (OR (95 % CI) = 1.224 (1.11 – 1.35), p < 0.0001), but no differences were seen with consent. Purchased food ED was unaffected by point of swap or consent, but reduced with number of swaps accepted (effect per swap (95 % CI) = −24 kJ/100 g (−35 – -14), p < 0.0001).ConclusionWithin category swaps did not reduce the ED of food purchases reflecting the observation that the use of swaps within an on-line shopping platform offered small potential gains in ED and a minority was accepted.Electronic supplementary materialThe online version of this article (doi:10.1186/s12966-015-0241-1) contains supplementary material, which is available to authorized users.

Highlights

Swaps offering consumers the opportunity to replace their usual food with a healthier alternative are used as part of social marketing campaigns (e.g. Smart Swaps in the Change4Life campaign, UK)
More swaps were accepted when offered at selection than at checkout (OR = 1.224 (1.11 – 1.35), p < 0.0001), but no differences were seen with consent
Within category swaps did not reduce the energy density (ED) of food purchases reflecting the observation that the use of swaps within an on-line shopping platform offered small potential gains in ED and a minority was accepted

Summary

Results

Response screening Of the 2683 unique participants who were assessed for eligibility, 1610 were randomized to one of the five study groups (See Fig. 1). Regression analysis of the energy density of the base food (the initial selections made prior to swaps being offered) revealed no significant differences for the intervention groups compared with the control group (effect size (95 % CI): 14 kJ/100 g (−32 – 60), p = 0.551), for swaps framed as consented compared with swaps framed as imposed (effect size (95 % CI): 38 kJ/ 100 g (−15 – 90), p = 0.159) or swaps offered at checkout compared with swaps offered at selection (effect size (95 % CI): −14 kJ/100 g (−67 – 38), p = 0.588). The acceptability rating for the intervention was significantly correlated with the number of swaps accepted (effect size per swap accepted (95 % CI): 0.562 (0.469-0.658), p < 0001)

Introduction

Method

Discussion