There is a writer we both know and love, you and I, who hates fat people. Every time there needs to be an example of personal unloveliness – from flatulence to bad manners – it is somehow bracketed with excessive girth. At first I just thought I was being oversensitive, but over time I realised that this expression of distaste, though possibly unconscious, was invariably there. I began to wonder whether, in adolescence, there hadn’t been some attempt on the author’s virtue by a very fat lady indeed.

This is just one small example of why it is a drag being big; few are hated simply for being slim.

So the wonder is why so many of us are fatter than we should be, or would like to be, and why so many of us will become that way. With cigarettes at least it was once considered cool to smoke; outside Tonga and Idaho it hasn’t been considered good to be plump for at least the past couple of centuries.

Yesterday the outward problem of obesity got it with both barrels at the conference of the gold-standard organisation in the field, the National Obesity Forum. The chairman of the forum argued that “levels of childhood obesity will lead to the first cut in life expectancy for 200 years. These children are likely to die before their parents.” Some have called for what I suppose would become known as a Lard Czar to coordinate the fight against flab.

I have to admit that, knowing what I know (and I know quite a lot about fat), I find this debate, as it is carried out in public, intensely irritating. The campaigners for change are always on the edge of exaggeration (“worse than climate change”), so fearful are they of inaction. This gives credence to the deniers who will invariably claim that the whole idea of obesity is a scare got up by the Government so as to deprive the public of its pleasures.

In fact the situation seems reasonably clear, which is that many people are fatter earlier than they used to be, and that chronic overweight gives rise – almost inevitably – to a series of health problems, including diabetes, that often lead to premature incapacity and early death. Staving off the effects of obesity costs an enormous amount of money in drugs such as beta-blockers and statins, and in hospital care. Anyone who says anything different is a fantasist.

Lordy, though, how we do look for the quick fix. Every year for the past decade there have been several stories in which scientists have either discovered the part of the brain, or the chemicals, responsible for our gluttony, and therefore the route to the possible magic cure, which will miraculously deprive us of our appetites and cause us to turn away the offered nibbles or pass by the cake-shop door. This summer fatties-in-denial everywhere were cheered by the suggestion from Louisiana that a virus might be changing stem cells into fat cells, thus helping to cause obesity.

All that was needed was the remedy, and I have lost count of the number of times that this or that antidepressant has been touted as an appetite suppressor, or the claim that – within a few years – a spray or a pill will be marketed to save us from ourselves. And then disappointment attends the realisation that the only tangible result from that magic fat-replacement food substitute is something distressing called “anal leakage”.

Yet we know the truth, just like Alice did: if you stick in more calories than you use up, you will get fatter; if you use up more calories than you consume you will get thinner. A fatter society tends to be one where people eat more high-density calorie foodstuffs and take less exercise. And that’s it folks, there is no more. No cure. No magic.

Of course, at this point it all gets complicated, because changing highly engrained and destructive patterns of behaviour is the hard part.

As an educated man I allowed my weight to rise to nearly 19 stone three years ago, committing slow suicide with the aid of Lindt chocolates, until packing myself off to an American reeducation institution to be told inescapably what I should already have known.

This amazing deliberate blindness doesn’t deter the easy-answers brigade. Some blame the food industry, as if they forced us to consume pizzas against our will. “It is the Government,” said the Lib Dem health spokesthing, Norman Lamb, at the weekend, “that must take responsibility for failing to do enough to halt the rise of this public health crisis.” Mr Lamb demanded urgent, though unspecified, action by the Government “to encourage healthier eating”. Something, perhaps, like the Indian Government’s sterilisation campaign of the 1970s, with forcible stomach-clamping for the recalcitrant. Nor is the answer “more school sports”. One part of the solution is certainly more exercise, and that could just as well be tap-dance as rounders. In fact tap-dance would be better.

Here’s a measure of the problem. The National Childhood Obesity Database, the largest database of its kind in the world, has found it difficult to garner accurate statistics because, it is thought, “heavier children” fail to turn up for weighing. Meanwhile, following Jamie Oliver’s campaign on school meals, Ofsted has discovered that the numbers of children taking the improved school meals has fallen. Analyse that for a second: the meals are healthier so the kids turn away from them. Instead their parents furnish them with lunchboxes, comprising, according to Oliver, “a cold, half-eaten McDonald’s, multiple packets of crisps and a can of Red Bull. We laugh and then want to cry.”

It is obvious that the problem is what is going on at home. Public policy can take down the barriers to healthier living by doing something to promote, say, safe cycling and walking at the expense of the bloody all-conquering motor car. But the message about obesity and lifestyle has to be internalised, as it eventually was over cigarettes, in order to work. We are going to have to convince ourselves that overfeeding and underexercising the kids amounts to neglect.

Best of all is the power of example. I am not a model for virtue when it comes to food, and the battle – as my colleagues can attest – is continual. But when I started running in 2005 I had no idea what would happen. Two years on, out of a family of five, three of us run regularly, and a fourth is about to begin. No mystery, just one bloody foot in front of the other.

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