Dieting is stupid. We know this. It doesn't work, it makes you grumpy, it gobbles up swathes of time and attention that could be more usefully devoted to other things - and now it's bad for your health as well.
A study published in the Journal of the American College of Cardiology found that women who repeatedly diet - "yo-yo" dieters - have lower levels of the "good" cholesterol, high density lipoprotein, which protects against heart disease.
Right, so we'll all stop being silly, shall we? Not likely. Yo-yo dieting is simply the expression of an ongoing dissatisfaction with appearance that pervades many women's lives. It is an exaggerated form of the skewed attitude to food and calories that affects many women.
Clearly, the gravity of the health risk depends on how fanatical you are about dieting. The study found that women who tried to lose 10 lbs three times in their lives were 12 per cent more likely than other women to develop heart disease.
But "trying" to lose 10lbs could mean almost anything. If your method is to live on Evian and chewing gum for a fortnight, you are almost certainly doing yourself damage; if, on the other hand, your idea of weight-watching is choosing a smaller slice of tart and skipping elevenses, you're probably all right.
Serious yo-yo dieters, forlornly ekeing out carrot sticks, then giving in to the temptation to stuff themselves with cookies and guilt, are easy to spot. But even among "normal" women, a seesaw approach to food and calories is endemic.
Foolish and unspeakably naff it undoubtedly is, but look inside the mind of an apparently well-adjusted woman and as likely as not you'll discover a running tally, of Points Scored (a no-fun, no-mayo chicken sandwich for lunch when what you really wanted was the all day breakfast) against Bad Things (raiding the bread basket, late-night pizza).
I don't think men do this. This is probably the one area in which women really are the dumb ones, particularly because, however obsessed with our weight most of us might be, we don't actually lose that much weight. That's why the tally never goes away - if we were good all the time, we wouldn't have anything to make up for.
Half a stone is enough to affect how your clothes fit, but not enough for anyone to do a double take, so the calorie scoreboard that is so much a part of the psychological landscape for women is seldom obvious to the outside world.
What's more, dieting, compulsive as it may be, is the stuff of solitary obsession rather than sparkling dinner table banter. Fussing about how you "really shouldn't", as if succumbing to the charms of the dessert menu was the naughtiest thing you've ever done, does make you seem a very dull person.
When you've been "good" and are riding high on the seesaw, unburdened by the memory of second helpings, the outlook seems sunny; when you're weighed down with the guilt of Bad Things, it taints your day. To make matters more complicated, the tally does not relate simply to food: exercise counts as Points Scored as well.
Indeed, unintentional exercise of the larking about variety garners the best kind of points - free points. Not even the accompanying Bad Things (nobody remembers to ask for slimline tonic after midnight) can mar the joy of waking up to the tequilashot of happiness you get from realising that not only did you dance for hours (the calories burned! the thighs toned!), you never got round to going for dinner.
A skipped meal is a Get Out Of Jail Free card, credit to be cashed in at a later date. The best thing about the seesaw regime is that, like a pay-as-you-go mobile phone, you can use your top-up cards at any point.
Lying in bed on a dark Monday morning, you can justify not going to the gym because you only had cornflakes for supper on Friday, so you have in effect already gone to the gym and burned a half supper-worth of calories, only in advance. Conversely, the memory of having ruined a day of restraint by shovelling in a half pound of pistachios during that dangerous 6.30 p.m. hunger period can niggle for a week.
Confusingly, while some good things are healthy (going to the gym, not eating chips), some unhealthy things still count as Points Scored. I once accompanied a friend, stricken with food poisoning, home to her (French) flatmate, who exclaimed: "You are so lucky! Throwing up is so good for the figure!"
The most ridiculous aspect of the whole ridiculous business is that it is simply too unscientific to work. Sometimes your concentration wanders: there is a whole chapter in the American diet bible The Skinny, entitled "What To Do If You Accidentally Drink A Coke Instead Of A Diet Coke."
Sometimes, you simply miscalculate: I remember a friend's indignation when I told her I'd read that brown bread, preferred as the "healthy" (read: thin) alternative, has more calories than white bread. "That's not fair!" she complained. Mad? Yes. Unusual? You wish.