When faced with a choice -- lower prices or healthier foods -- people are more likely to choose lower prices, according to a new study of food consumer shopping behaviours.

The study, published in the journal Marketing Science, found that when you give food consumers temporary incentives to buy healthier foods, they will likely choose those healthier foods.

But when you take away the discounts, consumers are more likely to return to old behaviours of buying the less healthy/less expensive options.

The study was based on research into the US Special Supplemental Nutrition Programme for Women, Infants, and Children (WIC), in which WIC gives vouchers for specific foods to mothers and their children aged 5 and younger. In 2009, WIC policy reform changed the composition of food vouchers, introducing vouchers to encourage the purchase of healthier products.

According to lead author Marit Hinnosaar from the University of Nottingham in the UK, evidence points to a decrease in purchases of healthier options after participants left the programme.

"During the incentive programme, vouchers were restricted to whole wheat bread and low-fat milk," she said. "Since some of these options tend to be more expensive, once the vouchers were no longer available for these products, consumers tended to choose items based on price."

Still, there was no measurable difference in the total quantities of products in the WIC vouchers during or after the programme. These products included bread, milk, fruits and vegetables, juice, eggs and cereal.

"A modest post-programme subsidy once programme participants leave the programme -- to incentivise healthier food choices -- may be a more sustainable way to lengthen the programme's impact and lead to long-term healthier food purchases," Hinnosaar said.