A new study, published in the journal PLOS One, tracked the price of 94 key food and beverage items from 2002 to 2012. Its findings show that more healthy foods were consistently more expensive than less healthy foods, and have risen more sharply in price over time.

Food prices in the UK have risen faster than the price of other goods in recent years, and this new research shows that the increase has been greater for more healthy foods, making them progressively more expensive over time.

While less healthy foods had a slightly greater price rise relative to 2002, the absolute increase was significantly more for more healthy foods - a total average increase of Pounds 1.84 per 1000kcal for more healthy food across the decade, compared to Pounds 0.73 for less healthy food.

In 2002, 1000 kcal of more healthy foods - as defined by criteria devised for the UK government - cost an average of Pounds 5.65, compared to purchasing the same quantity of energy from less healthy food at Pounds 1.77. By 2012 this cost had changed to Pounds 7.49 for more healthy and Pounds 2.50 for less healthy foods.

Researchers from the Centre for Diet and Activity Research (CEDAR) at the University of Cambridge who conducted the study say that this trend could result in people increasingly turning to less healthy food.

"Food poverty and the rise of food banks have recently been an issue of public concern in the UK, but as well as making sure people don't go hungry it is also important that a healthy diet is affordable," said lead author Nicholas Jones.

"The increase in the price difference between more and less healthy foods is a factor that may contribute towards growing food insecurity, increasing health inequalities, and a deterioration in the health of the population." The cost of diet-related ill health to the National Health Service has been estimated to be Pounds 5.8 billion annually.

The 94 foods and beverages in the study were taken from the Office of National Statistics' Consumer Price Index 'basket': the list of items used to measure inflation in the UK. The items included in the study were those which remained in the 'basket' for every year of the decade analysed.

To match nationwide food prices to nutrient content for each of the foods, the researchers combined datasets from the Consumer Price Index and from the National Diet and Nutrition Survey. This novel link allowed them to establish which foods were either more or less healthy using an objective assessment of the foods' nutrient content, as defined by the UK Food Standards Agency's FSA-Ofcom nutrient profiling model.

"The finding shows that there could well be merit in public health bodies monitoring food prices in relation to nutrient content, hopefully taking into account a broader selection of foods than we were able to in this study," said Nicholas Jones.

The study's authors say their finding that more healthy food is more expensive tallies with work from similar high income nations. They point to other studies indicating that the EU's Common Agricultural Policy - which subsidises production of certain goods such as dairy, oil and sugar - has the potential to affect public health by influencing the availability and price of foods.

"To help achieve long-term improvements in eating habits, we need to address the high and rising prices of healthier foods, which is likely to be influenced by a number of factors including agricultural policy and production, food distribution, and retail pricing strategies," said senior author Dr Pablo Monsivais from CEDAR in Cambridge.

"Additionally, there is growing evidence that targeted subsidies can promote healthy eating for people on low incomes."