A healthy diet is fundamental to good health, while unhealthy diets are a major contributor to burden of disease and health inequities. Supermarket environments influence the dietary choices of consumers and price discounts are known to influence purchasing decisions. If unhealthy foods were discounted more frequently or more heavily than healthier foods, this could adversely affect the diet and health of consumers. Previous research examining the association between product healthiness and discount frequency in supermarkets is limited. The primary objective of this dissertation was to determine whether non-core (less healthy) foods and beverages were discounted more frequently than core (healthier) products in two New Zealand supermarkets. Secondary objectives were to describe the size and type (simple discount or multibuy) of price discounts for core and non-core products.
Data was extracted from the online Countdown store and obtained from visits to a physical PAK'nSAVE supermarket in Christchurch, New Zealand. Countdown data for all in-stock food and beverage items was collected for 52 weeks. Eligible products were grouped into 36 categories and 923 subcategories. Each subcategory was classified as core, non-core or miscellaneous, using an approach based on previous studies and New Zealand and international nutrition guidelines. PAK'nSAVE in-store visits were conducted weekly for 14 weeks. The number of discounted products, the number of products with multibuy discounts and the total number of products were counted for seven core and 11 non-core food and beverage categories.
In the Countdown online store, discount frequency varied markedly between food and beverage categories. The main regression analysis found that non-core products were discounted significantly more frequently than core products. However, when a sensitivity analysis was conducted, with reclassification of some core and non-core products as "intermediate", no significant association was found between discount frequency and product healthiness. Discount size did not vary substantially by product category or core/non-core classification. The percentage of discounts that were multibuys varied markedly between food and beverage categories. It was higher for core than for non-core products overall but some unhealthy categories had a high percentage of multibuy discounts. Sports drinks and energy drinks had a particularly high prevalence of multibuy discounts and high discount frequencies overall. At PAK'nSAVE, the percentage of products that were discounted varied markedly between food and beverage categories. The percentage of products discounted was higher in non-core than in core categories. However, regression analysis found no significant association between the percentage of products discounted and category healthiness.
The results of this dissertation did not support the hypothesis that non-core foods and beverages in supermarkets are discounted more frequently than core products. This finding is consistent with the results of two UK studies. However, the absolute number of price discounts in the Countdown online store was higher for non-core than for core products and previous research suggests that the sales uplift from discounts is greater for less healthy products. Furthermore, the high frequency of discounts and multibuys in some unhealthy product categories, in particular sports drinks and energy drinks, has the potential to adversely affect the diet and health of consumers and to increase inequities in health. Potential health interventions related to price discounts include discounts for healthy products and restricting discounts for unhealthy products, on a voluntary basis or through regulation. Supermarket price discounts should be taken into account when modelling the effect of food and beverage taxes and subsidies. Further research is required to investigate the effects of price discounts on diet and to estimate the effect of potential discount-related health interventions.