"The Playtex 18-hour girdle helps prevent midriff bulge." This Sixties TV commercial introduced my unsuspecting childish psyche to the idea of the thickening waistline in one's middle years. This year, filming Dead Ringers, the idea was suddenly made flesh. I was sitting in position on set waiting to shoot a scene, all done up as news kitten Natasha Kaplinsky. As usual Mariel, the lissom Spanish wardrobe assistant, is buzzing about. She brushes off invisible bits of fluff and straightens my already straight collar - as usual - but then grabs the front of my jacket and gives it a good yank down. I look at her questioningly. She pats her own diminutive abdomen and says "Because ...", indicating my own less toned tum, much as if to say: "it had to be done, chica, you'll be glad I did that when you see it on the telly".

"The Playtex 18-hour girdle helps prevent midriff bulge." This Sixties TV commercial introduced my unsuspecting childish psyche to the idea of the thickening waistline in one's middle years. This year, filming Dead Ringers, the idea was suddenly made flesh. I was sitting in position on set waiting to shoot a scene, all done up as news kitten Natasha Kaplinsky. As usual Mariel, the lissom Spanish wardrobe assistant, is buzzing about. She brushes off invisible bits of fluff and straightens my already straight collar - as usual - but then grabs the front of my jacket and gives it a good yank down. I look at her questioningly. She pats her own diminutive abdomen and says "Because ...", indicating my own less toned tum, much as if to say: "it had to be done, chica, you'll be glad I did that when you see it on the telly".

I am told that the Spanish have a special word for this dreaded phenomenon: Michelinas - literally, lady tyres. Like the Michelin man. After I have stopped chortling (in a jovial, rotund sort of way), I am plunged into a deep gloom. I buy a book with the depressing title Fight Fat After Forty. It was the usual thing - eat less, exercise more and avoid carbs in the evening, plus lots of salutary reminders that women need smaller portions than men and, as you get older, your metabolic rate slows down, so you need less food. Bummer. I was rather looking forward to an old age of hairy legs, biblical sandals and not giving a toss about what I eat.

My immediate concern, however, is that I start filming again this week and the old Michelinas sadly remain. I have embarked on the Carol Vorderman Detox - lots of water, fruit and vegetables. "I'll have a P please Carol. In fact I'll have several ..." Yo ho ho. Of course I am not alone in my obsession with regaining a waistline. You can't turn on the telly these days without there being a programme with the words "Fit" or "Fat" in the title. As part of the launch of their new people-improving programme Fat Nation, the BBC has done a survey which shows that a surprising number of people are in favour of the Government making much stricter rules about what we eat. John Reid appears, looking ever more like a grumpy headmaster, and asserts in his "I'm-so-reasonable-really" fashion, that ultimately decisions about nutrition must be personal. In other words, that in a run-up to an election the Government does not want to be seen as the nanny state.

Au contraire, it seems that many of us are actually begging for the Supernanny state. Please, please we are lardy and lethargic and do not know what to put in our mouths next. Restrict us! Instruct us! But be warned. Stringent labelling on all those microwave meals we apparently can't live without will only be the beginning. Next thing you know, it won't be the gas man coming round to read the meter; you will open your front door to a tall severe-looking woman in a black suit and spiky heels with scraped-back hair and extremely prominent clavicles.

She will show you her government identity card and saunter uninvited down the hallway, arriving in your kitchen with a clipboard in her hand and a sneer on her lips. If you have so much as a sausage roll lurking in your fridge, then it's the naughty step for you - and if you still persist in giving your children Sunny D then you're definitely not getting a smiley face sticker to go on your wall chart this week.

When it comes to food, we all want teacher to tell us what to do. We have to go to Weight Watchers and be humiliated in front of the class with the incentive of a "silver seven" sticker every time you lose half a stone. At Slimming World, if you eat anything remotely calorific, it's called a sin. If you are an ordinary fat person, the likelihood is someone will make a television documentary about you, and a smug woman, whom you will find it difficult not to slap, will come round and throw all your frozen pizzas away.

How can we motivate ourselves to be healthier? Education is a start, but let's face it, I've read more diet books than I've had hot dinners (hardly), and it doesn't stop me from going over the top sometimes. It is all about self-control, and of course, balance.

But hey. Dr Gillian McKeith says You Are What You Eat (which may explain why she looks so much like an aduki bean) but actually you are a whole bunch more; intellect, imagination, personality, soul. Don't forget we need to nourish those, too.