My dad’s cousin, Pat, died recently. She was the largest person I’ve ever known; probably 30 stone. Many years earlier, however, her slim, fit husband had died from bowel cancer. Her last years were a struggle as her spine collapsed and she became wheelchair-dependent. But she died in her eighties and, apart from her mechanical problems, was essentially healthy until her sudden heart attack.

What really bedevilled Pat’s life was the rampant fatism that exists in our society. She was a fine lady with a great Lancashire take on life: Jane Austen transposed to Southport. But I noticed heads turning when I was with her; comments whispered behind hands - a disability apparent for all to see, but attracting a negative moral judgement that people don’t use about other traits.

To be so fat in our society is a cardinal sin, attracting waves of public disapproval. The parents of an obese child were threatened with having their son put in care recently. “Dr” Gillian McKeith bullies overeaters mercilessly on screen while cloaking her advice in a veil of questionable science. Barely a day goes by without another TV programme picking apart the daily habits of fat children or sad, fat women. Heat magazine and its ilk print unflattering photos of celebrities in their swimwear, inviting us to mock them. It’s a modern form of bear-baiting.

“But being fat is self-imposed!” say the moralisers, in self defence. Only partly. The environmental versus genetic debate rages in scientific journals. The consensus is that it’s a bit of both. And even if fat people eat more and do less than thin ones, does that make them evil?

Myths about fatness abound. US academic Paul Campos, author of The Obesity Myth, debunks many of them. For instance, the idea that Americans are getting fatter because of fast food is questionable. “The heaviest consumers of fast food in this country are single men in their 20s who weigh less than the average American,” says Campos.

Another common misconception is that fat people are lazy. Recent evidence from the Early Bird study in Plymouth, which is tracking the weight and activity of 300 children, found no link between how much kids do and what they weigh.

It’s not even true that rates of obesity are rising. Although obesity in men and children is still increasing in the US, the rate among women has slowed down. And where the US leads, we usually follow.

Although obesity is a national health problem, Campos says it is exaggerated by an industry that seeks to promote weight-loss products. “We are in the grip of a cultural hysteria driven by a $50bn [£25m] a year weight-loss industry which profits from increasing anxiety about weight and body image, and it’s something the government has bought into and helped promote.”

Thin taxpayers may argue that they shoulder the burden of obesity. Certainly, the National Audit Office says that obesity accounted for 18 million days of sick leave and 30,000 premature deaths in 1998. On average, each person whose death could be attributed to obesity lost nine years of life. Treating it costs the NHS at least £500m a year. Bad - but not as bad as alcohol abuse, which costs the NHS more than three times as much, at £1.7bn a year.

Of course, if people die young as a result of their bad habits, they cost the state less. But the fatists argue that obesity doesn’t just kill people young - they cost a lot because of health problems like osteoarthritis, diabetes and cancers that they bring on themselves. Maybe so, although I would argue that alcohol is a habit that causes more criminal damage, accidents and medical emergencies. A fat driver causes me no harm, but a drunk one might.

Personally, I’d rather not be obese. Life is easier in the normal weight range. But I know many people whose lives are totally dominated by their weight. Their capacity to enjoy life is weight dependent and they never eat a meal without feeling guilty. Many of these people are not obese. They are overweight with a body mass index (BMI) in the 25-30 range. Dr Mark Vanderpump, an endocrinologist at the Royal Free Hospital in London, says it is doubtful that these people are even at increased risk. “It’s not that clear cut,” he says. “Being mildly obese may be protective to your heart and may be better than being too thin. Those with a BMI of 25-30 don’t necessarily have a shortened life.”

Vanderpump says it all depends where the fat is. “Pear-shaped is protective. If you’ve just got a big bum, you may be fine. But people who look like an orange on sticks, the traditional apple shape, have fat around their internal organs and not just under the skin.” He says that waist circumference is more important than BMI.

“Lawrence Dallaglio probably has a BMI of 50, but he’s all muscle,” says Vanderpump. And he warns that men tend to think their waist size is three inches less than it actually is. “It’s the widest part of you, round the umbilicus, not on the hips where many men wear their trousers.”

So how big is too big? Over 40 inches for men and 35 inches for women is deemed obese and that’s when the risks of cardiovascular disease really kick in.

Vanderpump says that people should be aware that there is an almost inevitable weight gain between the ages of 40 and 60, possibly as much as 1kg a year. So people who are just a bit overweight in their forties will probably be obese by their late fifties unless they eat less and do more.

Perhaps that’s a choice we want to be free to make, without feeling too bad about it. I think we deserve to know that being a bit overweight is probably not harmful and may even be protective. Obesity is harmful, but so are lots of things we do to ourselves. And while obese people do harm to themselves but not to others, they do not deserve the negative press and moral vilification that is so widespread. Fatism is just about the only irrational prejudice that is still deemed acceptable. Let’s get rid of it.

Independent News and Media Limited