'Change4Life Smart Swaps': quasi-experimental evaluation of a natural experiment.

OBJECTIVE: To evaluate the impact on food purchasing behaviour of the 'Change4Life Smart Swaps' campaign to encourage families to make small changes to lower-fat or lower-sugar versions of commonly eaten foods and drinks.

DESIGN: Quasi-experimental study comparing the proportion of swaps made by an intervention group (267 families who had signed up to the 'Smart Swaps' campaign promoted through various media, including television and radio advertising in early 2014) and a comparison group (135 families resident in Wales, signed up for 'Change4Life' materials, but not directly exposed to the 'Smart Swaps' campaign). During weeks 1, 2 and 3 of the campaign participants were asked to record their purchases of dairy products, carbonated drinks and breakfast cereals, using a mobile phone app questionnaire, when making a purchase within the category.

SETTING: England and Wales.

SUBJECTS: Families registered with 'Change4Life'.

RESULTS: In weeks 2 and 3 a significantly higher percentage of the intervention group had made 'smart swaps' than the comparison group. After week 3, 58 % of participants had swapped to a lower-fat dairy product compared with 26 % of the comparison group (P<0·001), 32 % of the intervention group had purchased a lower-sugar drink compared with 19 % of the comparison group (P=0·01), and 24 % had made a change to a lower-sugar cereal compared with 12 % of the comparison group (P=0·009).

CONCLUSIONS: In the short term a national campaign to change purchase habits towards healthier products may have some merit but the sustainability of change requires further investigation.