Leading brands in so-called unhealthy foods have suffered a dip in sales, according to trade magazine The Grocer.
Walkers lost sales overall but its Sensation range gained
There are signs that Kit Kat, Walkers Crisps and Kellogg's Frosties have been losing customers to brands they think are healthier, claims the study.
Sunny D lost 30% of sales despite a £7.5m campaign to counter perceptions of the drink as sugary, it says.
Kath Dalmeny, of the Food Commission, said people were "getting wise to what is in some of these products."
The report into the UK's top products was published on Saturday.
It says Britons spend more on crisps than all the other major European countries put
And sales of crisps increased last year by 2.2% to just over £2bn.
Top Products Survey
Nestle Kit Kat down 9.1%
Twix down 4.3%
Total chocolate up 0.2%
Walkers Crisps down 2.1%
Sunny D down 30%
Diet Coke up 4.5%
Mineral water up 21%
*last 12 months, figures from The Grocer
But Walkers Crisps, the country's leading brand, experienced a sales loss of 2.1% to £510m.
Sunny D was worth around £150m a year at the end of the 1990s but
sales over the past year fell from £37.9m to £26.6m.
Sunny D manufacturer Procter and Gamble, which considered selling the brand,
said in a statement: "The relaunch of the brand in June has shown some strong
positive business results, with brand share stable or up throughout 2003."
Campaigners have criticised breakfast cereals as being too high in sugar content.
The survey claimed sales of Kellogg's Frosties fell 7.4% from £43.7m to £40.4m, although Kellogg's Coco Pops were up 1.9%.
Sales of Diet Coke have overtaken the standard version for the first time, increasing 16%.
Keith Wells, director at brand consultancy Dragon, said: "Some of the figures
are surprising, particularly the dip for brands like Kit Kat, but it shows that
health issues have really kicked in."
Kath Dalmeny, from healthy eating campaign group the Food Commission, said:
"The results show that people are getting wise to what is in some of these