Britain is deserting the Whopper, according to the American fast-food chain Burger King, which is facing an uphill struggle to cope with our new concern for healthy eating.

The world's second-largest hamburger vendor pinpointed its 650 British restaurants as a source of falling sales against a backdrop of strong business almost everywhere else in the world.

Burger King's chief executive, John Chidsey, said the company had to make a $3m (£1.6m) cash injection to "fortify" its British operation against a "challenging operating environment".

In a quarterly earnings statement, Burger King said its global profits leapt by 82% to $40m in the three months to September, aided by new Stacker sandwiches and a discount Value Menu. Its shares jumped 7% on Wall Street.

But it bemoaned its poor performance in Britain, blaming it on "perceptions about obesity and food-borne illness and increased competition from sandwich shops, bakeries and other new restaurants that are diversifying into healthier options in response to nutritional concerns".

Warnings about Britain's looming obesity epidemic have catapulted healthy eating into the headlines in the past year, aided by Jamie Oliver's campaign for healthier school dinners.

Mr Chidsey said the company had made certain concessions - it does not put salt on chips in Britain unless customers requested it. A children's menu includes milk and "grapple" - grapes and apples.

He said the chain had a "have it your way" promise that allowed customers to ask for tailor-made hamburgers with variations such as extra lettuce and tomato.

Burger King's problems are in stark contrast to the fortunes of its larger rival, McDonald's, which said last month its sales in Britain were strong thanks to refurbished restaurants, a new marketing strategy and options such as carrot sticks, apple dips and walnut salads.

Burger King has 11,220 outlets, serving more than 11 million people a day.