Inside every svelte and finely-honed runner is a great big blubbery lard-arse, trying to get out.

I once engaged a coach to help me crack three hours for the marathon. (I didn’t fail – he did.) I asked him what, as a serious athlete, I should and shouldn’t eat. He replied, ‘If you’re running fifty miles a week, matey, you can eat whatever you sodding well like.’

After many years of dietary experimentation, I can testify to the truth of this theory. It’s a wonderful blessing. You can stuff down six chicken kormas, a jumbo-size pork pie and your body weight in Special Brew, with a flagon of condensed walrus fat for good luck, and next morning you’ll still be able to count your ribs in the mirror.

However, the converse is also true. If you don’t run fifty miles a week, you’re condemned to wash down a rocket salad with a low-fat mineral water on alternate Tuesdays until the day you slit your wrists and drink your own blood, just for the relief of tasting something.

It’s a tough one. You can look great and implode from sheer boredom. Or you can conduct yourself like a human liposuction machine and end up being winched out of bed to star in a Channel 5 freak show, live from Brighton Pier.

But in the words of the Buddha and Tony Blair, there is a Middle Way. My coach’s way.  The Blackford Way. Namely: do it to death, but make sure you get up next day at dawn and run like a bastard. You’ll throw up in hedges and bleed from the eyeballs. In fact, it will be an altogether ghastly experience. But in the words of the Buddha and George Harrison, All Things Must Pass (George being an excellent example of this principle).

By the end of your run you’ll be ashen-faced, sick-splattered and teetering on the brink of cardiac arrest. But look on the bright side: your metabolism will have been charging along like a mad bugger and a hangover that would otherwise have lasted past sundown will have evaporated in forty-five minutes.

What’s more, all those dead calories from the thirteen glasses of Puerto Rican Merlot and the kebab from the Serbo-Mongolian Grill will be steaming harmlessly away in a hedge instead of pumping you up like a prize pig in a county show.

And after a couple of showers and a tiny vodka, you’ll find you can stride off to work with a certain jaunty confidence. You have jogged to the limits of human endurance and laughed in the face of death, run the ultimate race against your grossly-enlarged liver and won.

And you’re still only half the weight of your boss, who thinks a Good Time is pruning the buddleia and de-lousing the cat.

You, dear Reader, have got it all.  You are a demi-god. You are Pete Docherty without the Priory bills. You are Kate Moss without the Pete Docherty.  You can plumb the depths of depravity, then soar effortlessly away like an eagle on wings of fire.

Welcome to Planet Skinny where, for just a few hours of horror and excruciating pain per week, you are granted a passport to shameless self-abuse – your personal, platinum American Excess card.

In the end it’s a juggling act. If one hand gets the upper hand, you become your dad and sprout a set of pruning shears. The other hand, and you turn into Jade Goody.

So my advice is, steer down the Middle Way as if your life depended on it.  Because it probably does.