From the taunting of the chubby child in the playground to cruel jibes at fat people in work and social settings, few could doubt there is widespread prejudice against the overweight. However, according to research reported in Evolution and Human Behavior some people suffer abuse because being too fat is mistaken by the brain for a sign of disease.

Researchers say the immune system can be triggered into action at the sight of obesity because it doesn't like the look of what it sees, and associates it with infection.

Just as it orchestrates attacks on viruses and bacteria and triggers nausea at the hint of bad food, so it sends out signals of disgust in some people at the sight of an obese body that is designed to encourage avoidance and survival.

The finding comes just days after research in The New England Journal of Medicine suggested that obesity is contagious, in a social rather than bacteriological sense.

"Antipathy toward obese people is a powerful and pervasive prejudice in many contemporary populations. Our results reveal, for the first time, that this prejudice may be rooted in multiple, independent mechanisms. They provide the first evidence that obesity serves as a cue for pathogen infection,'' say the University of British Columbia researchers.

They say a behavioural immune system appears to have evolved in humans that is designed to detect body signs that are related to disease, like rashes and lesions. The sight of them triggers disgust as well as negative attitudes and avoidance. The system errs in favour of over-reacting because failure to react to a real danger could be fatal.

Researchers carried out a number of experiments, including word associations and tests where they compared the reactions and views of men and women to obesity.

The results show that people who agreed with comments such as "it really bothers me when people sneeze without covering their mouths" were more likely to agree with statement such as "if I were an employer looking to hire, I might avoid hiring a fat person". The greater the fear of disease, the stronger the negative feeling about obesity.

But Clarissa Dickson Wright, the surviving half of the Two Fat Ladies cookery duo, said the research merely served to cover up the general prejudice of narrow-minded people. "In the 1960s there were a lot of bigoted people who were anti-black, anti-Jewish, anti-everything but when they couldn't get away with that any more they turned into food-Nazis instead and began attacking people who were fat," she said. "I suspect that this is what really drives people to be negative about fat people rather than an unconscious reaction.

Ms Dickson Wright said there was an aversion in America about even using the word "fat", as she found when her programme was shown there.

"Reporters asked me: 'How do you feel about the title of the show?' and I said: 'Which part? There's two of us and I hope you're not suggesting we're not ladies.' They just couldn't say the word."

"It's a way to put sexism on the agenda," said Beth Ditto, the lead singer for The Gossip.

"All this stuff completely negates what feminism stands for, and you can't act like that's not connected to other issues."