Putting calories on restaurant and cafe menus cuts intake by around 12 per cent, research suggests.
A review led by Cambridge University found that consumers given information about the calories in each meal were likely to think twice about what they chose.
Researchers examined evidence from 28 studies, and found that the best research suggested that the presence of labels cut calorie intake by around one eighth.
Next month, Public Health England will launch a campaign urging people to limit lunch and dinner to 600 calories, with 400 calories for breakfast, in a bid to help people cut back.
The findings suggest that the presence of labels means consumers choose healthier options, or leave more of their food on their plate.
On average, the calorie reduction would amount to around 70 calories on a 600 calorie meal.
It follows warnings that the average Briton typically consumes 1,000 more calories than they estimate every day - while women have around 800 calories more than they account for.
The team noted that there was still some uncertainty around this effect and that further well conducted studies are needed to establish the size of the effect with more precision.
The Review’s lead author, Professor Theresa Marteau, Director of the Behaviour and Health Research Unit at the University of Cambridge, UK, said: “This evidence suggests that using nutritional labelling could help reduce calorie intake and make a useful impact as part of a wider set of measures aimed at tackling obesity.”
Professor Susan Jebb from the University of Oxford commented: “Some outlets are already providing calorie information to help customers make informed choices about what to purchase. “This review should provide policymakers with the confidence to introduce measures to encourage or even require calorie labelling on menus and next to food and non-alcoholic drinks in coffee shops, cafeterias and restaurants.”
Professor Ian Caterson, President of the World Obesity Federation, said: “Energy labelling has been shown to be effective: people see it and read it and there is a resulting decrease in calories purchased.”
A Department of Health and Social Care spokesman said: "We know that childhood obesity is one of our greatest health challenges. Our world-leading strategy recognises this threat, with comprehensive plans to tackle inequalities through taxes on sugary drinks, funding further research and helping children to exercise more.
“However we have always said that this was the start of the conversation on obesity, not the final word - and we have not ruled out further action if the right results are not seen.”
Alison Tedstone, chief nutritionist at Public Health England, said: “With around a quarter of our calories coming from food on the go, including takeaways and deliveries, we need clear and consistent information on menus at the point of choice.
“Some companies are already doing this, but too often menus are an information-free zone - we need bigger and bolder commitments to help people make healthier choices and avoid obesity-related health problems.”