A new study published on bmj.com today found about a sixth of fast food customers used calorie information and, on average, bought food with lower calories since the introduction of a labelling system in the US.
US researchers found there has been a small but positive impact from a law introduced in 2008 in New York requiring chain restaurants with 15 or more branches nationally to provide calorie information on menus and menu boards in the city.
Obesity rates in the US are at an all time high in both adults and children and currently a third of adults and 17% of children and teenagers are obese. Several studies support an association between fast food consumption and excessive energy intake, but customers often underestimate the number of calories in restaurant meals and before 2007, nutrition information was seldom available at the point of purchase.
So a team of researchers decided to assess the impact of the calorie labelling regulation on the energy content of individual purchases at fast food restaurants in New York City. High street chains in England are about to embark on a similar, though voluntary scheme, as part of the government's Public Health Responsibility Deal.
Surveys were carried out during lunchtime hours in spring 2007 (one year before the regulation) and in spring 2009 (nine months after its implementation) at 168 randomly selected locations of the top 11 fast food chains in the city.
Adult customers provided register receipts and answered survey questions. Data from 7,309 customers in 2007 and 8,489 customers in 2009 were analysed.
Overall, there was no decline in calories purchased across the full sample. However, three major chains saw significant reductions.
For example, at McDonalds, average energy per purchase fell by 5.3%, at Au Bon Pain, it fell by 14.4% and at KFC, it dropped by 6.4%. Together, these three chains represented 42% of all customers in the study.
However, average energy content increased at one chain - Subway - by 17.8% where large portions were heavily promoted.
Analysis also showed that 15% of customers reported using the calorie information and, on average, these customers purchased 106 fewer kilocalories than customers who did not see or use the calorie information.
The researchers say that calorie labelling is only one part of a framework to address the obesity epidemic and call for additional strategies to reduce energy intake on a population basis. "Special attention should be focused on educating customers on how to interpret and use nutrition information," they conclude.
In an accompanying editorial, Dr Susan Jebb from the MRC Human Nutrition Research Centre in Cambridge believes that labelling is a step forward, but changes in food supply must follow. She writes: "Calorie labelling will help consumers make an informed choice about what they eat, but sustained improvements in the nation's diet will require a transformation of the food supply too."