Fat is not a feminist issue, despite what feminists used to say. It is a class issue. Well-to-do, well educated people are rarely fat, still less obese. You see few fat children in private schools. Fatness and obesity are directly related to low income and low education.

A fat map was published last week by Dr Foster Intelligence, showing the areas with the fattest populations, and sure enough the poorest industrial areas in the north of England and in Wales produce the most obese people. The problem seems to be getting worse, fast.

You hardly need expert medical data analysis to understand that. You need only to go to a few supermarkets. At a Tesco in western Scotland this summer I was astonished by the number of horribly obese shoppers waddling round the aisles with their elephantine children, who could not possibly have squashed themselves into an ordinary one-person chair. Young women, with eyes reduced to slits by the pressure of the fat on their faces, laughed grimly with each other as they scanned the shelves. And this is a rich country.

Even though the vast Oban Tesco is full of good food, the trolleys at the checkout were heaped with stuff that is either useless or positively bad to eat – crisps, snacks, swizzlers, twizzlers and guzzlers, cheesy dips and fatty whatsits, cakes puddings and pies, heavily dusted in additives. The obese seem to fill their carts regularly with several times their own weight in eatables that can make them only fatter, that they shouldn’t eat and that nobody should produce, as if they were determined to lay down yet more adipose tissue. Yet you rarely see such bloated people and trolleys in smart supermarkets in rich areas. These days you can easily tell people’s precise socioeconomic bracket and body weight by the contents of their trolleys.

Obesity seems to be the issue of the day, possibly because we are still in the silly season. Coincidentally last week, Andrew Lansley, the Tory health spokesman, spoke against obesity in a long speech to the Reform think tank. He was widely understood as saying that fatties have only themselves to blame; they must take responsibility for themselves and their weight because “we all have a choice”. And while that is a slightly unfair take on his speech, he does seem to mean something of the sort. Yet at the same time he offers what’s now called a whole raft of measures to stop people getting fat. This is awkward for Conservatives; either you interfere with people’s choices or you don’t. Empowerment, a word he used, is often just a weasel word for state intervention.

The question is why a Conservative government should interfere at all in people’s inalienable freedom to choke on deep-fried Mars bars if they choose to. The argument is that the fat and the obese (people with a body mass index over 30, which is something you could spot without a calculator) cost the country squillions in lost productivity and increased National Health Service costs. The obese tend to develop serious illness, particularly heart disease and diabetes, and are, generally speaking, crocked up and expensive to look after.

Somebody somewhere has come up with a figure for the cost of all this, which Lansley quotes – £7 billion a year, for what it’s worth. Last year’s Foresight report said this cost could go up by six times by 2050. And fat is getting fatter so fast. According to NHS figures, the proportion of obese men in the population rose during Labour’s time in office from 13.2% in 1993 to 23.1% in 2005. Among women it was even worse, from 16.4% to 24.8%. That is nearly a quarter of all women. If you consider people who are not obese but overweight (with a BMI of 25-30), 46% of men in England are overweight and 32% of women.

Fat is also an ethnic issue. According to NHS figures published in 2006, Irish and black Caribbean men had the highest incidence of obesity (25% each) and among women black Africans had 38%, black Caribbean 32% and Pakistani 28%. So, with migration trends and immigrant fertility, the costs of obesity are going to rise fast as well.

However, I wonder how much, if anyone knew the facts, the final cost of obesity would be to the taxpayer. For fat people die sooner and obese people die much sooner than others, thus relieving the NHS and the economy of their needs. It’s true that obese people need expensive treatment for diabetes and heart disease before they die, but that might easily be offset if they had significantly shorter lives – and they do. Current thinking seems to be that the obese die between five and seven years earlier than otherwise they would.

Few papers I’ve looked at on this subject discuss the possible cost-benefit of obesity, although one from an insurance company coyly mentioned the advantage to pension providers if a person died before he reached pensionable age. For years I used to argue that smokers were a net benefit, purely financially speaking, to the exchequer, because they died early. I still feel rather proud of being the first, I believe, to get a known expert (Professor Richard Peto in 1993) to agree publicly to this idea, now accepted. Might not the same be true of obesity? The real drain on the NHS is geriatric medicine; the obese might not reach old age.

If the only reason for interfering with what fat people eat is how much it costs the rest of us, perhaps we should leave them alone. It’s well known that obesity (and fatness) are associated with poor education, poor housing, poor employment or none, low expectations, low opportunities and all the rest. These are all social ills that this government has been trying to deal with for more than a decade. Yet little has improved and obesity – as an indicator of that fact – has swollen vastly while Labour has been in office. What prevents obesity is a good income, a good education, good opportunities and the kind of background that develops self-confidence. Prosperity, in short.

Obesity cannot be defeated by taskforces, better labelling on packets or investing in health accreditation schemes. This has all been tried and has failed. In the presence of a complex problem, and in the absence of a workable solution, perhaps it is better to leave people to their own devices. Nobody can pretend they don’t know what they’re doing. They should be left alone to do it.

minette.marrin@sunday-times.co.uk

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