Restaurants could be forced to introduce a "traffic light" labelling system on menus to help curb rising levels of obesity, it was revealed to The Independent on Sunday last night. Diners could be faced with green, amber and red circles to guide them to the healthiest dishes on the menu.

A green circle would show food is safe and advisable to eat, while amber foods should be eaten in moderation. The unhealthiest food would carry a red circle warning of high fat, sugar and salt content and eaten only occasionally.

Supermarkets already follow a similar voluntary code, but some firms have refused to comply and show guideline daily amounts of ingredients (GDAs) instead.

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Ministers are stepping up their anti-obesity campaign by considering a radical extension of the system to restaurant chains to persuade people to choose a healthier diet.

This month, New York will introduce a scheme forcing all chains of restaurants and fast food outlets to list calorie content next to their food. The city argues it could prevent 30,000 cases of diabetes and reduce the number of people suffering from obesity by 150,000 over five years.

The Department of Health is watching the New York scheme closely and is actively considering a version for the UK. It is hardening its policies on public health as obesity levels continue to rise. Two-thirds of adults and a third of 10-year-olds are classed as overweight or obese.

The Food Standards Agency has already held talks with some restaurant chains on a traffic light system. The move is likely to face stiff resistance from the food industry, which would be forced to spend money updating menus. It is also controversial for smaller chains because many dishes do not contain standardised levels of ingredients, while menus change from season to season.

McDonald's, which is affected by the New York regulations, said it was already having talks on introducing guidelines in the UK. "We have provided nutritional information on our UK packaging since 2006. The information we provide is the nutritional value of the menu item and how it relates to daily nutrient recommendations (GDAs). We also provide the information on the back of all tray liners."

In supermarkets, Asda and Marks & Spencer have agreed to the traffic light code, but Tesco claims the amber circle is too ambiguous and instead shows percentages of fat, sugar and salt in GDAs.

The Conservatives criticised the move. Health spokesman Andrew Lansley said: "We're in favour of giving people the information necessary to construct a healthy diet, but all we've had from Labour so far is dithering and delays. Food labelling must include GDAs, not just traffic lights. We need to emphasise the importance of a good diet, not just a good or bad food."

A Department of Health spokesman said it was considering the plan "in the future as part of a healthy food code of good practice".

In 2006, for the first time more money was spent on eating out than on meals cooked at home.

On the menu

McDonald's

Quarter pounder: fat 21g; carbs 37g; protein 23g.

Grilled chicken salad deluxe: fat 1.5g; carbs 7g; protein 21g.

Burger King

Cheeseburger: 19g fat; 27g carbs; 21g protein.

Vanilla shake: fat 9g; carbs 73g; protein 13g.

Pizza Express

Margherita pizza: fat 4g; carbs 40.5g; protein 13.5g.

Mixed leaf salad with olive oil dressing: fat 33.6g; carbs 4.8g; protein 0g.