All you can eat: the 5,000 calorie diet

Cakes, hamburgers, chips and ice cream - it may sound like a fantasy diet, but for Matt Kimpton, who needs 5,000 calories a day just to stay alive, mealtimes are no picnic

It's called the CF Diet, and it's everything you've ever looked for. No calorie control. No forbidden foods. As much sugar as you like. As much fat as you can take. Thousands of calories a day, and you always stay thin.

The catch? You always stay thin. And without those empty calories, you starve to death.

Oh, it's all a hilarious journalistic conceit, of course. It's not really a diet; not in the sense of some media bandwagon you can jump on and off at will. It may sound like some novel carbohydrate/fat mix, but CF actually stands for cystic fibrosis: a genetic condition known for causing the body to produce unusually sticky mucus. Since that includes the lungs, and since the lungs are not a great place to store unusually sticky mucus, the long-term effects tend to include dying horribly of lung disease. But as anyone who's watched Alien will know, mucus gets everywhere. The lungs might be the killer, but the same stuff in the pancreas means an almost total inability to digest fat.

Thirty years ago that meant the mother of all low-fat diets - the sort where instead of using margarine instead of butter, you have dry Ryvita and be thankful. But then, in the early Eighties, enzyme supplements were developed that allowed CF patients to digest fat... a little. Almost overnight, the diet turned upside-down: suddenly we were told to consume as much fat as humanly possible in order to get enough to stay alive. (So how come we stayed alive before, I hear you ask? Well, most of us didn't, that's how come. I was one of the lucky ones.)

To most people, that sounds like the medical pronouncement of your dreams: go forth and gorge. But this isn't just a Mars bar after lunch and the occasional guilt-free Jaffa Cake. A normal, healthy person should be eating 2,000-2,500 calories a day to maintain a stable weight - which in practical terms means craving an extra few hundred after dinner and bingeing on crisps at the weekend. Under the new CF diet, however, the recommended calorie intake is closer to 5,000. That means eating everything you eat in a day, plus everything you eat in another day... every single day. And then bingeing on crisps.

I know I should feel lucky. The kitchen on a CF ward looks like an Aladdin's cave of temptation for the average dieter. Baskets of sweets and biscuits lining every flat surface - huge Tupperware boxes groaning with untouched snacks - the very air toxic with Angel Delight. But of course the average dieter isn't allowed in: only us patients who, tragic victims of human nature, don't want it. Instead we sit forlornly in the middle of it all, skinny and desperate, longing for a salad.

On the bright side, it drives dieticians mad (the one thing uniting dieters across the spectrum being our loathing for professional dieticians). I've lost count of the consulting rooms I've sat in, scales glaring at me from the corner, while waif-like professionals plead with me to fit in just two more meals a day. Why can't I eat a Bounty bar each morning? Why do I insist on eating celery? Why won't I swap my ketchup sandwiches for cake? The answers - that I was brought up on a no-fat diet and never got the taste for chocolate; that I'm full, and have been since I was 15 - just don't cut the ice. Desperate measures are called for: one dietician, channelling the race-memory of Nans throughout history, suggested I have a glass of sherry and watch Ready Steady Cook. Another taught a course, like Gillian McKeith in anti-matter form, where she told us to follow fat people round supermarkets and buy what they bought.

It doesn't work like that, of course. But we'll try anything once - anything to get that healthy store of fat to help fight off infections. Patients swap ruses for reaching their target weight, like WeightWatchers seen through a looking-glass of lard. Start with pudding. Add crisps to everything. Drink gold-topped milk; put butter on vegetables; grate cheese on to eggs; put sugar on cereal, cream in soup, honey on ice-cream, on biscuits, on cake... Eat when you're hungry, eat when you're thirsty; eat when you're bored, eat before bed.

The trouble is, there are limits to how far you can go. My mate Ross, for instance, an assistant chef, at one point needed 7,000 calories a day: enough, by normal standards, for a 200lb man made entirely of pure muscle, or half an average horse. (Admittedly he was weight-training at the time, but he's five foot seven and weighs nine stone. The Incredible Hulk he is not.) And you can't do that. Three cooked meals a day doesn't even begin to buy it, even when it's the ideal fry-up, roast and curry CF combo. Snacking doesn't do more than cover the tip.

Received medical opinion is that - as with unlikely diets since time immemorial - the solution mostly comes down to milkshakes. You know the sort: pre-packaged doses of thick, barely drinkable ooze calling themselves things like "The delicious, take-anywhere shake!" or "A high-energy, nutritionally complete, orange-flavour milk-shake-style supplement!", or in extreme cases "A strawberry flavoured long-chain triglyceride fat emulsion!" (I don't suppose even they could do much with "Tastes like paint!"). Packed with 300 calories each of protein, fibre, fat and ick, they add up to half a packet of Jaffa Cakes a time - so if you can stomach seven a day you're ahead by the average daily diet before you even start eating.

But if you can't? If you simply haven't got the biology for it any more? If you're like my mate and fellow CF patient Mikey, 21, and after years of mismanagement have been left weighing six stone with a stomach the size of an apple?

Well, then you're down to the wire. It's the CF equivalent of that moment in horrified Channel 4 obesity documentaries when a medical team come in with a crane to unpeel you from the sofa. Naso-gastric feeding is an option for some, involving a tube fed through the nose and down the back of the throat, and currently enjoying a bit of a comeback in Guantanamo Bay. But otherwise the only solution is a surgical one: white coats and scalpels and anaesthetic, the whole lot; cutting you open to insert a feeding tube directly into the stomach, leaving a big plastic tap on the outside through which you can be drip-filled, overnight, with a high-fat, artificial, pre-digested pulp.

Doesn't sound too appetising. But it's one that ultimately most CF patients plump for, as mounting infections push their calorie requirements ever higher - and their bodies even thinner. "It makes you eat more, because it stretches your stomach," Mikey explains, less than enthusiastic. "But all the weight that goes on me just goes on my belly and my bum, so I look like an Ethiopian. My arms just look like bone, and my shoulders stick out so much they could have your eye out. I'm not saying I'd like to look like Mr Universe, far from it. I'd just like some muscle and flesh covering me... instead of just skin."

Except he's got no right to complain, has he? Still less Ross, who admits that to go really skinny - "To actually, this is going to sound terrible, to look like a CF" - is one of his greatest fears. Because we at least get the upside of our upside-down diet. Not like you lot, unhappy with your lumpy bodies, paranoid about every inch and every stolen Quality Street. We are, after all, the eighth and greatest wonder of the world; the last great hope of man; the impossible dream: thin.

Hah. Might as well tell you "at least you're fat". (And you're not, I swear, it's just the light.) Because that's how it feels, to us. That's how much it's a perfect reversal of the ordinary world - where weight gain is a source of pride; where you'll sooner plump for surgery, tubes and discomfort than face another day of cake; where "Hey, you've put on weight!" is a friendly greeting rather than an insult. Where you sit with your partner like Jack Spratt and his wife, staring wistfully at his lettuce while he yearns for your tiramisu.

That's how dumb the CF diet is. Never eating what you want. Never getting a day off. Never being in control. Just hating your shape, and dreading the scales, and spending every day in all-out war against a body whose needs are utterly, perfectly, exactly upside-down to your desires.

In fact, come to think of it... it's just like every other damned diet going.

The CF diet: 5,000 calories a day

* 8am

Start the day with a build-up drink in a choice of flavours "to avoid taste-fatigue".

Running total: 300 calories

* 9am

A fry-up, light on beans and heavy on lard (800 calories).

Running total: 1,100 calories

* 11am

Another delicious build-up drink, and the chocolate bar of your choice (600 calories).

Running total: 1,700 calories

* 1pm

Roast dinner, or the Ross Special: stir-fry with chips (800 calories).

Running total: 2,500 calories

* 3pm

Another build-up drink. Yummy. Feeling bloated yet? (300 calories)

Running total: 2,800 calories

* 6pm

Curry and chips for dinner, and don't spare the dessert (1,000 calories).

Running total: 3,800 calories

* 9pm

A build-up drink - in fact better make that two (600 calories).

Running total: 4,400 calories

* Midnight

A crucial time for extra energy: sandwiches, crisps, chocolate or frosted cereal, and one last build-up drink for the road. 600 calories - and then it's time to start dripping into your overnight feed...

Running total: 5,000 calories