UK supermarket price promotions are more likely to lead to an increase in sales of less healthy foods than healthier choices in supermarkets, according to a study published today. However, the study of almost 27,000 UK households found that supermarkets were no more likely to promote less healthy over healthier foods.

Price promotions are commonly used in stores to boost sales through price reductions and stimulate impulsive purchases by increasing items' prominence through tags and positioning. However, there is growing concern that such promotional activities by the food industry may contribute to poor dietary choices and might lure consumers away from healthier, higher priced options.

"There's plenty of anecdotal evidence, but very little empirical evidence, about the impact of price promotions on people's diets," explains Professor Theresa Marteau, Director of the Behaviour and Health Research Unit at the University of Cambridge. "In this study, we examined whether less healthy foods are more likely to be promoted than healthier foods and how consumers respond to price promotions."

A team of UK researchers, funded by the Department of Health, studied detailed data on purchase records of all foods and beverages by 27,000 households in the UK. Over 11,000 purchased products from 135 food and drink categories were assigned healthiness scores - following UK Food Standards Agency (FSA) criteria - based on the FSA nutrient profiling model.

Published today in the American Journal of Clinical Nutrition, the results show - perhaps surprisingly - that on the whole less healthy items were no more frequently promoted than healthier ones. However, after accounting for price, price discount, and brand characteristics, the magnitude of the sales increase was larger in less healthy than in healthier food categories. A 10% increase in the frequency of promotions led to a 35% sales increase for less healthy foods and a just under 20% sales increase for healthier foods. The researchers believe this may be because products from less healthy food categories are often non-perishable, while those from healthier food categories - in particular fruit and vegetables - are perishable: stockpiling during promotion may therefore be more likely to happen in less healthy food categories.

The study also found that households of a higher socioeconomic status tended to respond to price promotions more than those from disadvantaged backgrounds, for both healthier and less healthy foods. The researchers suggest a number of reasons, including the fact that making the most of promotions may involve stockpiling items while they are on offer, requiring financial resources and more space to store products.

"It seems to be a widely held idea that supermarkets offer promotions on less healthy foods more often than promotions on healthier foods, but we did not find this to be the case, except within a minority of food categories," says Dr Ryota Nakamura from the Centre for Health Economics at the University of York, who carried out the research whilst at the University of East Anglia. "Yet, because price promotions lead to greater sales boosts when applied to less healthy foods, our results suggest that restricting price promotions on less healthy foods has the potential to make a difference to people's eating habits and encourage healthier, more nutritious diets."

Citation: Nakamura, R et al. Price promotions on healthier vs. less healthy foods: a hierarchical regression analysis of the impact on sales and social patterning of responses to promotions in Great Britain. AJCN; 11 Feb 2015