Food and nutrient availability in New Zealand: an analysis of supermarket sales data

OBJECTIVE: To examine food and nutrient availability in New Zealand using supermarket sales data in conjunction with a brand-specific supermarket food composition database (SFD). DESIGN: The SFD was developed by selecting the top-selling supermarket food products and linking them to food composition data from a variety of sources, before merging with individualised sales data. Supermarket food and nutrient data were then compared with data from national nutrition and household budget/economic surveys. SETTING: A supermarket in Wellington, New Zealand. SUBJECTS: Eight hundred and eighty-two customers (73% female; mean age 38 years) who shopped regularly at the participating supermarket store and for whom electronic sales data were available for the period February 2004-January 2005. RESULTS: Top-selling supermarket food products included full-fat milk, white bread, sugary soft drinks and butter. Key food sources of macronutrients were similar between the supermarket sales database and national nutrition surveys. For example, bread was the major source of energy and contributed 12-13% of energy in all three data sources. Proportional expenditure on fruit, vegetables, meat, poultry, fish, farm products and oils, and cereal products recorded in the Household Economic Survey and supermarket sales data were within 2% of each other. CONCLUSIONS: Electronic supermarket sales data can be used to evaluate a number of important aspects of food and nutrient availability. Many of our findings were broadly comparable with national nutrition and food expenditure survey data, and supermarket sales have the advantage of being an objective, convenient, up-to-date and cost-effective measure of household food purchases.