Worryingly, a fifth of the population is now classified as obese

Mintel report

The market for so-called "functional foods", such as breakfast cereals, energy drinks and low-calorie spreads, reached �667m last year, and was set for further growth, Mintel said.

The overall food market, meanwhile, remained flat.

New image, better sales

Breakfast cereals earned top spot in the functional foods league, with sales up from �80m in 1999 to �175m last year.

But Mintel credited much of the growth in the sector to products which have been repositioned as health foods through, for example, marketing drives emphasising a product's vitamin content.

"Many [people] will be attracted to everyday foods and products that offer health benefits without a major change in eating habits or lifestyle, so long as taste is not compromised," said Elvira Doghem-Rashid, consumer goods consultant at Mintel.

The sector's success could see many other products rebranded as health promoting.

"Provided that repositioning stimulates sales growth, the expense of repositioning will be worthwhile to manufacturers," Ms Doghem-Rashid said.

Do they work?

The growth in sales of functional foods came despite a report last year casting doubt over health promotion claims.

A study by the Consumers' Association's Which? magazine found that some of the products were no more beneficial to consumers' health than cheaper alternatives.

And Mintel talked of other signals that the overall health of Britons was not growing as fast as might be imagined from the Friday's report.

The proportion of Britons who smoke has increased by four percentage points to 52% since 1998.

Less than one third of adults visit GPs for annual check-ups, compared with a figure of almost a half four years ago.

And Mintel found that obesity ranks as "one of the lowest consumer health concerns".

"Worryingly, a fifth of the population is now classified as obese," Friday's report said.

"This compares to less than 10% in the 1980s."

Friday's report raises hope that Britons appreciate the importance of healthy foods.

But it is as yet unclear whether they realise that any benefits gained from functional foods are not in proportion to the amount consumed.