A Department of Health-funded report today called for supermarkets to be hit with new restrictions on the promotion of unhealthy food, despite finding supermarkets do not skew deals in favour of such products.

A report published by the University of Cambridge found that promotions on food classified under FSA criteria as unhealthy had more impact on sales because they tended to be non-perishable products and were more likely to be stockpiled by shoppers than fresh items such as fruit and vegetables.

However, the report admitted that the proposed restrictions on promotions would do nothing to tackle the huge problem of health inequalities, with evidence showing that better off families were most likely to respond to promotions of both types of food. Researchers suggested that wealthier people were better equipped with the cognitive skills to respond to promotions and were more likely to buy healthier food even when it as not on promotions, than their poorer counterparts.

This follows widespread fears that poor families in particular may have been responding to price cuts at supermarkets to feed unhealthy diets.

Published today in the American Journal of Clinical Nutrition, the study looked at the shopping patterns of almost 27,000 UK households with more than 11,000 purchased products from 135 food and drink categories assigned healthiness scores following UK Food Standards Agency (FSA) criteria – based on the FSA nutrient profiling model.

The results showed that unhealthy items were no more frequently promoted than healthier ones, but that the magnitude of the sales increases were 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.

Researchers said this may be because products from less healthy food categories were often non-perishable, while those from healthier food categories – in particular fruit and vegetables – were perishable with stockpiling during promotion therefore more likely to happen in less healthy food categories.

However, the report found that poorer families were less affected by the impact of promotions than those form a wealthier background. It found that households from a higher socioeconomic status tended to respond to price promotions more than those from disadvantaged backgrounds, for both healthier and less healthy foods.

“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.”

The report comes a week after Professor Susan Jebb, chair of the Responsibility Deal Food Network, attacked supermarkets for failing to sign up to DH plans to limit the promotion of unhealthy food, which have been repeatedly mooted under the deal.