I'm not one of those people who usually break the law. I feel guilty at the sound of police sirens, and always do a very dull 29 in a 30-mile-an-hour zone. But here I am, engaged in the kind of internet-based crime generally reserved for fraudsters, pervs and fundamentalist jihadis.

I am on an illegal diet. I bought it on eBay. What a wondrous marketplace it really is - the place to pick up a crumb of the moon or one of Britney's celebrated pubic hairs. Now, you can buy a better body, all at the click of your voracious little mouse. So I bought 20 sachets of LighterLife diet drinks, paying a stranger from Wolverhampton a vastly inflated £101 for the privilege.

Four days later, my new body arrived in the post: four 'nutritionally complete' raspberry shakes, four vanilla, several chocolate, some mushroom soups and a number of packets stamped with the noncommittal words 'Thai Chilli' in an inadequately small font. Not exactly a menu to delight the senses, granted. But this LighterLife lark, I told myself as I stared at those miserable compressed food packs, would work wonders.

I know this because my friend Raquel spent 100 days on LL and dumped a massive three stone - about the weight of a five-year-old child. Another acquaintance pulled off the same trick following a divorce and is now wearing jeans for the first time in 20 years. One suspects the ex is now ruing the day; she, meanwhile, looks like the cat that got the cream (but didn't drink it). These two used LighterLife as it is intended: they got the blessing of their doctors; they also attended weekly group meetings of cognitive-behaviour therapy, which apparently makes the whole endeavour sustainable in the long term. They even had a jaunty website (www.lighterlife.com) and a glossy magazine to gee them along, full of encouraging stories about people called Barbara who've lost four stone in the time it takes to boil a kettle.

But there's a catch: in order to qualify for the programme, you must be at least three stone overweight. My paltry seven pounds didn't qualify. And so I cheated. I saw a diet that worked, I wanted a slice of that pie, so went off piste and did it my way. No meetings. No doctors. No shame.

As I emptied the first sachet of contraband cement into a cup and added scalding water, I kept an eye on the door, half expecting it to be broken down with a battering ram and men in bullet-proof vests to come pouring into my kitchen demanding immediate surrender. The drink was disappointing. No men in uniform. And a clarty, thickened texture not unlike tile grout.

Still, day two and I persevered. Along with the powders, enormous quantities of water are prescribed, and I'm convinced the sheer amount of time on the loo means your access to the fridge becomes limited and the weight evaporates. Whatever. It worked, give or take the odd kill-me-now headache; I lost seven pounds in seven days, which is pretty much the holy grail for dieters like me, who can't stand to hang around waiting for the weight to drop away in tiny increments. After a week of purgatory and purge, I'm back at my ideal weight and have bought a bikini to celebrate.

Great. But here's the thing: this illicit dieting has made me realise the hideous lengths we women go to in order to lose an inch here or a pound there. Weight and its loss have become the infatuation of our generation. I can't be alone.

I probably care a good deal less than a Hurley or a Posh, who are so trapped under their obligation to be thin that they emerge from the experience looking like they've been eviscerated, then steam-rollered and hung out to dry. It's so obviously a waste of so many things that they barely need cataloguing - time, joy, money, life. And yet we persist. We buy endless books, try endless supplements, potions, lotions and goos. We're hooked.

Just lately, a slew of new dieting techniques has emerged which can only mean more effort, more angst. I have dutifully been drinking a few tablespoons of rapeseed oil and sugar water between meals to trick my persecuted body into storing less fat. (I don't know if it will, but so what? It just might.) I'm also thinking of trying an extract of magnolia bark which may help weight loss by lowering cortisol levels; or perhaps bitter melon, which is said to stabilise blood sugar and control appetite - all available over the net at the sort of bloated price reserved for silly mares like me. But, hey: when they come to arrest me, at least I'll be a reasonable size 10.