Development of a simple and valid indicator to assess the relative availability of healthy versus unhealthy foods in New Zealand supermarkets

Abstract

The in-store availability of healthy versus unhealthy foods is likely to influence consumer purchasing behaviours and dietary habits. The evidence is mixed and the widely varying methods to classify foods and measure availability may contribute to this. To generate comparable data on in-store food availability a standardised methodology and simple, valid, and reliable indicators are needed. A literature review of 112 studies was performed on methods measuring in-store food availability. Based on this, linear shelf length and variety were chosen to test in this study. Three local and international nutrient profiling systems were applied to a database of 13093 packaged foods available in New Zealand supermarkets and compared to select the healthiest and unhealthiest food categories for inclusion in this validation study as the ‘gold standard’. In total 22 healthy and 28 unhealthy groups were selected. The shelf space and variety of these 50 categories were measured in 15 New Zealand supermarkets across three different chains. Repeatability was tested in one supermarket by a second researcher. The validity of six different simple indicators against the ‘gold standard’ for the relative availability of healthy versus unhealthy foods in supermarkets was tested. Data from fifteen supermarkets showed a range of 17.7m – 36.2m of healthy foods for every 100m of unhealthy foods, and 26 healthy varieties for every 100 unhealthy varieties (27 if size excluded). The ratio of the shelf length of fresh and frozen fruit and vegetables versus soft drinks, crisps, sweet biscuits and confectionary showed a no difference between methods (difference =0.023, Wilcoxon p=0.36) and significant correlation (r=0.75, p=0.00) to the ‘gold standard’. The linear shelf length of a simplified selection of food categories can be used as a simple indicator of the ratio of healthy to unhealthy foods available in New Zealand supermarkets. This simple indicator provides a faster and easier method of measuring the availability of healthy versus unhealthy foods in supermarkets. Consistent use of this method in future research and monitoring would enhance comparability of food availability between different studies, and can inform healthy food environment interventions and policies. Keywords: food availability, consumer retail food environment, INFORMAS, supermarkets