FOLK buy less fast food from outlets that show calorie details, a study found.
Nutritional labelling led to a four per cent drop in the number of calories purchased.
But US researchers found the effect wore off over time.
They said calorie-labelling alone is not enough to make major inroads into the obesity crisis.
Two in three Brit adults are too fat.
Fast food chains in the US have had to label calorie contents of their dishes since 2018 to help customers make healthier choices.
Officials are considering a similar policy in the UK.
The Harvard University team analysed sales data from 104 restaurants for two years before labelling and one year afterwards.
They found that immediately after displaying the info, customers bought 60 fewer calories per transaction — a reduction of around four per cent. But a year on, the drop was 23.
Experts said the fall was “largely driven” by people buying less items, rather than healthier options.
Oxford University’s Asha Kaur said: “Although the results might be disappointing to some, small changes to calorie intake can have meaningful effects at population level.”