The British Heart Foundation has moved away from TV advertising to target hard-to-reach 11- to 13-year-olds with a series of "gross" online videos about junk food inspired by the TV shows Brainiac and Banzai.

The BHF, which has in the past created TV ads to shock viewers about the grim reality of heart disease, has developed a campaign that will only use the internet to target children.

A series of three online videos show children eating junk food while being presented with the products that foods high in fat, salt and sugar can contain and the effects they can produce.

One ad, hosted by a character called Sick Rick, shows a child trying to complete an obstacle course while weighed down with 10kg of liquid fat – the amount produced in a year from eating one chocolate bar and one bag of crisps a day.

The ads have been directed by Pete Boyd-Maclean, the director of offbeat Channel 4 comedy Banzai, and produced by Archie Lauchlan, who worked on Sky One science show Brainiac.

The adverts will all be housed on a central website called junkmonkeys.tv and are also being seeded on websites popular with young people such as Piczo, Bebo, YouTube and Microsoft Live.

The campaign, created by Microsoft-owned digital ad agency Avenue A Razorfish, feeds into BHF's wider Food4Thought initiative. Three further ads will follow the current set.

"With junk food advertisers increasingly using their websites and advergames to target kids in their playtime, it's important that we can provide some basic balance in this arena," said Betty McBride, the BHF director of policy and communications.

Isba, the body representing UK advertisers, criticised the charity's view that advertising is to blame for the increasing problem of childhood obesity.

"It is slightly unfortunate that the British Heart Foundation still feels it necessary to attack the ads for food and drink products that are enjoyed by millions in Britain," said Ian Twinn, the public affairs director at Isba, the British advertisers' body. "As we know, advertising does not make children fat."

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