Ten-year trends in the price differential between healthier and less healthy foods in New Zealand

Aim To measure the relative change in price of healthier and less healthy foods over 10 years in New Zealand. Methods Foods in the New Zealand food price index were classified as healthy and less healthy (WHO Europe Nutrient Profile Model) and by degree of processing (according to the NOVA classification). The change in price from February 2007 to January 2017 was analysed using a mixed model for repeated measures with healthiness (or level of processing), season and time added as covariates. Results Eighty-eight (of 155) relevant items had sufficient information on weight and healthiness. The trend of increasing food prices over time was similar for healthier and less healthy foods and between the three categories of processing. There was a statistically significant interaction (P = 0.014) between seasons and healthiness of foods, and seasons and degrees of processing (P < 0.001). The price of healthy foods and minimally processed foods fluctuated more by season compared to less healthy foods and processed foods. Conclusions Food prices increased over time with no significant difference in the rate of change for healthier and less healthy foods, and between foods of different degrees of processing. This method can be used to routinely monitor relative changes in food prices according to healthiness.