Sales of sugary and fatty snacks are falling for the first time in years as the obesity epidemic encourages shoppers to choose healthier options.

Chocolate, biscuits and pizzas high in salt or cholesterol have been shunned by the public in an apparent reaction to publicity about the nation's flabbiness. Taking their place in shopping baskets are mineral water, yoghurts and smoothies.

The big snack manufacturers Walkers Crisps and Cadbury have lost tens of millions of pounds of business because of the switch. Many are now urgently reformulating products to make them more healthy by reducing saturated fat and salt levels.

The trend, revealed today in The Grocer magazine's annual survey of food sales, adds to evidence that Britons are trying to become healthier. In an opinion poll for the National Consumer Council in October, two-thirds of adults said that they had changed their eating habits or exercised more in the past year.

According to The Grocer's Top Products survey, sales of some unhealthy foods plummeted in 2005, such as Pot Noodle, down 23 per cent, and Sara Lee gateaux, down 74 per cent. Frozen pizza, one of the least healthy options, lost 3 per cent of sales along with "sugar confectionery" such as mints.

The amount of money spent on chocolate rose by 1 per cent, less than inflation, but there was a divide between the performance of the most and least calorific products. Fatty Creme Eggs were down 13 per cent while brands believed to be "lighter", such as Aero, rose by as much as 28 per cent.

Overall, sales of crisps fell by 1 per cent while those of nuts, a more nutritious option, rose 10 per cent.

In just one indicator of the pain to the snack manufacturers, sales of Walkers Crisps fell 7 per cent, costing the company £30m in lost sales. The Grocer said crisp manufacturers were "working overtime" to develop better-for-you options and promote the health credentials of their products.

The trend towards healthier eating was evident in biscuits, where sales drifted down for Jaffa Cakes and Penguin but rose for healthier Ryvita and Alpen bars.

Probiotic drinks that reputedly promote "friendly" bacteria in the stomach leapt by 50 per cent. Meanwhile, there was a boom in foods containing Omega 3, which is claimed to aid the development of children's brains and improve their behaviour. Some milk is now fortified with Omega 3.

The mineral water market leaped £50m to £576m - up 10 per cent. Sales of fizzy drinks such as Pepsi and Dr Pepper remained stable but there was a rise in the sale of fruit juices. Sales of Innocent Smoothies trebled.

The survey was evidence of a strong shift to healthy eating, according to Danielle Tolson, of AC Nielsen, which collects the information from bar-code scans from stores across Britain.

"What we are seeing is that offerings that are slightly healthier are doing better. Certainly people are becoming more aware of health," she said.

Claire Hu, The Grocer's marketing editor, described 2005 as a "challenging year" for the food and drink industry, as people's preoccupations with their waistlines started to affect sales.

The survey's findings coincided with the publication of a study by the Health and Social Care Information Centre showing that between 1993 and 2004, obesity among English men rose from 13 per cent to 23 per cent. In women obesity increased from 16 per cent to 23 per cent. The research showed a rise among children of body mass index - a measure of weight in relation to height. Since 1995, the average BMI for boys increased from 17.6 to 18.1, and in girls from 18 to 18.4.

Out with Mars and pizza, in with Alpen and yoghurt

We're buying more ...

* Mineral water, fruit juices and smoothies

* Probiotic drinks that help your stomach

* Lighter crisps with less saturated fat

* Smaller chocolate bars like Cadbury Flake

* Crackers and cereal bars

* Premium dark and organic chocolate, such as Lindt and Green & Black

* Low cholesterol spreads such as Flora

* Rice and fresh and dry pasta

* Malt loaf, which has a healthy image

* Wine from big name brands from Australia and California

We're buying less...

* Calorific chocolate bars like Mars and Snickers

* Sugary sweets such as Polo and Maynards

* Ordinary fatty crisps. Pringles are down eight per cent

* Traditional chocolate biscuits such as Penguin

* Sugary orange drink Sunny D

* Fatty biscuits Viennese whirls, lemon slices and Battenburgs

* Tinned vegetables and fruit

* Frozen ready meals, particularly frozen pizza

* Fizzy drinks popular with children

* Ready to drink cocktails such as Smirnoff Ice