A new diet in January is predictable: that's why I started my latest diet at the end of last October. By January, I hoped, I'd be sufficiently encouraged by positive results.
Every perennial dieter probably knows Groucho Marx's jest about quitting smoking: "Giving up is easy. I've done it hundreds of times." Starting a diet is easy. I've done it hundreds of times.
Any diet works when you adhere to it, however zany it seems. Because all diets operate on the same law: eat less food, and especially less of the wrong kind of food (and drink less alcohol or anything sugary).
Sticking with the rules is the problem. Faddy diets become a pain in the neck. Even quite sensible diets - cutting out, or cutting down on, sugars and carbohydrates - can interfere with your way of life. If you have to travel for your work, sandwiches may often be the only convenient way of putting fuel into your body.
Obesity expert Zoe Harcombe says that's something we should remember: the body needs energy to keep on the go. Starving yourself all the time empties your energy tank.
She's also against dieters taking out gym membership at the beginning of the year. Gym sessions use up energy and can make you exhausted: then you have a muffin afterwards as a compensatory treat. You're better off taking an active attitude to everyday tasks - walking more, using the car less, stairs rather than lifts.
Garret Fitzgerald, a taoiseach who could be described as a true intellectual, once responded to a civil servant's description of some new policy scheme with the immortal words: "That's all very well in practice, but how does it work in theory?" Me too, Garret. I like any idea to have a nice theory behind it, before we get into the practicalities.
And thus was I drawn to the nostrums of the diet guru Dr Michael Mosley. His diet philosophy is based on evolutionary analysis and draws on a traditional religious practice: fasting. Fast for two days a week - say, keep your calorie count down to between 600 and 800 cals a day - and you'll soon have a figure like Nicole Kidman.
No, the last bit isn't true. Nicole Kidman's long legs and slender body come from her genes. But the theory of fasting will deliver a slimmer version of yourself, which is what every dieter craves.
How old is Homo Sapiens? Our species has been around for about 200,000 years. And for the last 199,900 of those, most of humanity has had to practise fasting. We lived by famine and feast. Food stocks would get depleted through the winter, and by February there was little enough to eat: not coincidentally, perhaps, Lenten fasts would start around this time of the year. Virtually all religions have periods of fasting, recommended for spiritual reasons, but it now turns out they deliver considerable health benefits too.
And so, the human body was adapted, through millenia, to the fasting cycle. If there wasn't enough food around, the body told itself "live off the present resources for a period of fasting". So it used up the fat that it had stored, and embarked on repairing itself generally too.
The practice of fasting fell out of favour as food became plentiful, refrigeration, jet planes and microwaves rendered meals conveniently available to us all year round. And thus we grew obese.
Fasting theory as effective diet really stacks up. But I also have a cousin who has done brilliantly on the 'Fast Diet', by keeping to 800-1,000 calories a day for two days a week. She's lost an impressive amount of weight and feels terrific. So the practice proves the theory.
Yet not every diet suits every individual. Just as medication will soon be tailored to our individual DNA, so diet will one day be adapted to our physical profile, and also to our personalities. In the meantime, I adapted Michael Mosley's diet theories to my own disposition and circumstances.
Fasting all day I found a bit depressing. But fasting from 6pm at night until about 7.30am the next morning is just fine for two or three days a week. Sometimes I went to bed hungry, but that's an aspect of the fasting experience that can be curiously rewarding. And how much energy do you need as you wind down of an evening?
But I feel the need for a decent breakfast, and it would be tough to forego a square of chocolate with a morning coffee.
There's an old formula for this adaptation of the fast diet: breakfast like a king, lunch like a lord, sup like a pauper.
Diets have to suit your way of life. I lost some weight a couple of years ago with a slimming group, but the weekly attendance didn't suit my peripatetic travels, and anyway I grew bored with the meetings. Any variation of the fasting diet could be uncongenial for those who live in a couple or family relationship. For women who sit down to an evening meal after putting the kids to bed, supping a mug of Bovril is not much of a cordial occasion.
Theories are dandy, but outcomes are the test. And yes, on January 1 the scales showed that I had shed seven and a half pounds since the end of October. At last, I hope, I've found a diet pattern that really works for me.