Doctors today called for a ban on all food advertising aimed at children under 12 in a bid to tackle the UK's increasing obesity epidemic.

The British Medical Association's (BMA) annual conference was told of an obese 11-year-old boy unable to walk short distances without getting out of breath due to his weight.

Delegates at the conference in Llandudno, Wales, overwhelmingly backed a motion "that all commercial food advertising aimed at under-12s should be banned".

Johann Malawana, a medical student from Essex who proposed the motion, said it was well-known that junk food was a major cause of childhood obesity.

He said: "The food industry spent £300m in 1999 on promoting unhealthy food products. The food industry has been using more and more famous sports personalities to promote junk food and fizzy drinks to make them seem cool. We would not stand for tobacco companies advertising to our children as they do in the third world, why should we stand for it on the advertising of junk food?"

He called for junk food adverts to only be broadcast on TV after the 9pm watershed. "Restrict this adverting to after the watershed and replace it with a campaign on public health promoting a better lifestyle for all our young people."

Andrew Rowland, a paediatrician from St Mary's hospital in Manchester, said food advertising was promoting poor diets that led to obesity.

Dr Rowland said: "Young children are being bombarded with advertisements for food that is damaging their health. They may not at this stage have developed the reasoning capabilities to recognise the adverse effects this food is having on their health."

He added: "Just last week in the outpatient clinic I saw an 11-year-old patient whose weight was 85kg (13 stone five pounds). This boy was considerably shorter than me and 20kg heavier.

"That may not sound a huge amount but this child could not walk from the waiting room to the consultation room without being short of breath. He could not do physical education at school."

Peter Tiplady, a public health doctor from Cumbria, said there was evidence that up to 99% all food advertising during children's TV was for fatty or sugary foods.

"Against a background of evidence that a diet high in fat, sugar and salt are detrimental to health, this selective targeting of children by food advertisers is unwelcome, unjustified and absolutely unforgiveable," said Dr Tiplady.

Keith Brent, a paediatrician from Northampton general hospital, also criticised celebrity endorsements of junk food.

He said: "Almost every day in my clinic I will see a child who is overweight or has been eating poorly. Most often the parents throw their hands up ... and say what can I do? They demand this, they demand this sort of food all the time.

"I know that I could tell them how they should be eating healthily...but what is my voice compared to everything they see on TV? How good do I look next to Gary Lineker telling them to eat crisps?"

The issue of food advertising is being examined by ministers as part of a consultation on a white paper to improve the nation's health.