Here’s a fact to help you at the next pub quiz: the average Vietnamese pot-bellied pig lives a mere 10 to 15 years. You can explain why, too, and get a bonus point.

It’s all about waist-to-hip ratios: your trouser size divided by your bottom circumference. Because recent research has revealed that the health risk caused by fat is linked not to your weight but to where you wobble most. Blokes with beer guts look away now: getting flabby around your waist significantly increases your risk of heart disease. Love handles? Coffin handles, more like. No wonder our porcine pal turns up his trotters so prematurely.

Apparently, unlike excess padding elsewhere, waist fat increases resistance to insulin, which sets off a cascade of metabolic events promoting atherosclerotic plaque so that . . . OK, we’ve moved from pub quiz to University Challenge. Forget the science. The key message is: pear-shaped good; apple-shaped bad.

Which, oddly, is reasonably good news for doctors. I can stop using the traditional calculation of obesity, the body-mass index. This tedious process requires me first to check your weight (because you’d lie if I asked you) and your height (because “I’m sure I’ve shrunk, doctor, that’s why I look fatter”). Then I have to do some complicated maths, involving squaring the hypotenuse and taking away the number I first thought of, to tell me what I knew already. Which is that you’re too fat.

Now - as the hip measurement isn’t that important - I’m just supposed to ask your waist size. If you’re a male over 40in or a female over 35in, it’s not good news: you’re seriously limiting both your lifespan and your choice of clothes at M&S.

From your point of view, there remain some positives in this hip-waist-ratio stuff, at least if you’re in the heavier proportion of the population. You now have a new line of attack. After all, for years you’ve had to put up with consultations with your GP characterised by increasing levels of desperation.

These start with the battle cry of the beefy: “I can’t be overweight; I don’t eat a thing.” This is inevitably followed by a fastidiously detailed litany of everything you do, in fact, eat, to demonstrate how negligible it all is - which, frankly, is as much fun for GPs as having needles stuck in our eyes. So we wave a white flag in the form of a thyroid test, colluding with your idea that it must be “your glands”.

Of course, the result is normal. So you’re back, and this time I persuade you to go away by stuffing a diet sheet in your hand and showing you the door while you can still fit through it. Then we suggest WeightWatchers. Then exercise on prescription. Finally, medication. The result? The side-effects make you lose the contents of your bowel. But no weight.

It’s at this point that you start wailing that no one ever helps you and that something must be done. Why, you demand, through moist, blubbery snivels, can’t you be stapled? My eyes wander from the clock, which shows I’m running late, to your quivering lips, to the stapler on my desk - and, for a fleeting moment, a decidedly nonvocational thought crosses my mind.

Just as well, then, that you now have a new line of attack. “It’s not that I’m too fat,” you declare clutching the hip-waist-ratio news stories. “The fat’s just in the wrong place.”

Presumably you want the lard liposucked from belly to bottom so you end up with ratios like Kate Moss wearing pantaloons. Sorry, not sure that would work. Sorry, too, that my eyes glaze over as they do in every consultation with the corpulent.

I’m not fattist. And I do want to help. It’s just that those who succeed in losing weight usually do so off their own bat. Whereas those who consult me think that I can cure a lifestyle issue and so are doomed to fail. Cheer up, though. There’s always the pub quiz to look forward to. Steer clear of the pork scratchings, though, for obvious reasons.

Dr Copperfield is an Essex GP. He also writes for Doctor magazine. Mark Henderson is away