A few years back the object that I wanted to possess again and again was a packet of Camels. The golden animal, the pyramid, the three palm trees, the absurd name, were so cool. It was a pleasure just to walk into a tobacconist’s and ask for them. To take off the Cellophane. To smoke the brand that Bogart smoked — before he died of lung cancer.

I recognised the selfsame feeling of desire, brought on by proximity to coolness, a few weeks ago in a shop in the West End. If I bought what was on display then, just as with the Camels, I would be associated with something neat. I would be enhanced. The place was Niketown, and the objects of desire were bits of running gear: the sweat-wicking black tights with the white tick, the lightweight over-jacket, the red and black mesh jogging top, the gel shoes, the integrated Nike watch and heart-rate monitor. Trendiness in the service of vice and selfdestruction had been transformed into trendiness in the cause of virtue and healthiness.

Even the most incidental collision with modern British popular culture will suggest that this struggle is at the centre of our national conversation (fringe alcoholism and obesity versus the Olympics and Pilates), and — more subtle — at the centre of our conversations with ourselves. Our appetite for diets, food advice, exercise suggestions and health products seems be utterly unrestrained. We are what might be called binge-magical thinkers. If we read something often enough, do a bit of this, drink a bit of that and stretch the other, we’ll cheat ageing and defy death.

My own struggle became critical last year. I was medicated for high blood pressure and was gradually blobbing out to the extent that I refused to get on the scales any more, always giving my weight as 17st. I ended up, at the suggestion of a very good friend (only a very good friend could have suggested it) going to a place in Miami called the Pritikin Longevity Institute. There, for two weeks, everything important was measured: blood, urine, body composition, the arteries of my neck — the lot. I went into Pritikin heading for diabetes. I came out 16lb lighter, with a transformed diet and an exercise habit — and without my beta-blockers. Those I had swapped for a lifetime’s need to know all about how I was doing. My magical thinking works.

A decade or so ago Helen Fielding captured the psychology of this in the early Bridget Jones. Bridget wasn’t so much looking to defeat mortality as to find a man, but her stratagems were similar. Smoke less, eat less, lose weight. If she were virtuous she would get the thing that she desired, so every day she measured her vices, hoping to achieve sufficient control over them to deserve a husband.

The Bridgets (and, for that matter, the Bens) of 2005 face a much more complex series of calculations, because information — our thirst for it and its availability — has altered everything. In only one way has the situation been simplified. We now understand that there is a single possible “Good” figure for the number of cigarettes smoked in a day — the roundest figure of all. Everything else, however, has gone mad.

If we were to make up a new Bridget Jones tabulation of vices and virtues, we would now have to add several entire categories. The idea that simply consuming a number of possibly harmful substances, and the fact of being this weight or that weight, tells you how well you are doing in the battle against personal evil, seems wonderfully naive, the product of a simpler time. We should now have to add to “Consumption” a separate heading marked “Body”, yet another for “Output” (or, if you prefer, “Exercise”) and a fourth devoted to “Mind”.

Body first. Measuring your weight is only useful, as psephologists tell us, when looked at as a trend. On its own it doesn’t tell you how fat you are, how ugly or how doomed. All you really need to know is whether it is going up or down, and how fast. And now even the measurement of success, the body mass index or BMI, is regarded as flawed. I can vouch for this, as my personal trainer (no, don’t snigger) has a BMI that says she ’s obese when in fact she looks like a younger, happier Kelly Holmes. For men the critical figure is now regarded as being the one that best shows the distribution of fat — the waist to hip ratio. A bigger tum than hip size is associated with a higher risk of cardiovascular episodes. Before I got religion last spring I had a ratio of 1.2, which was very bad. It’s now 0.9 or so, and as a result models fall at my feet and I will never die.

There’s your blood pressure reading. I do that once a week, but I’ve never really taken to heart-rate measuring because of all that finger-on-the-vein stuff. One for women especially is the occasional bone-density scan to warn of the risk of osteoporosis. There’s stuff you can do about it. And, if it wasn’t mad, I’d have my blood and urine analysed once a month to see whether my good cholesterol, or HDL, is winning its eternal battle against the evil internal Bin Ladenites of the LDL.

Then there’s all the physical stuff consequent upon taking up regular exercise, such as diagnosing and avoiding injury. Since I slid, rather fraudulently, into the camp of regular runners, I have become aware of phenomena such as shin splints and plantar fasciitis, which, despite how it sounds, is not a problem first recognised in Mussolini’s gardener. But look, we have to be reasonable, so we’ll keep post-exercise stretching out of the table because we need plenty of room for diet.

Diet and Su Doku. The world’s gone mad. I am completely convinced, both by my own experience and by the science, that what you eat makes a spectacular difference to how you feel and how well you are. But the proliferation of diet material, in which it is nearly impossible to separate the quackery and faddishness from the common sense, puts the subject beyond summary. I’ll tell you what I think should be in there: fibre, fruit and veg, wholegrain, complex carbohydrates and attention to key metals and vitamins. What should be avoided are almost all fats, high-density calorific stuff that takes no time to eat and a five-mile run to work off, processed and refined foods, and foods with a lot of salt. As it happens, this is not a million miles away from the diets that talk about the glycaemic index, or GI.

And then there’s detox, of course, which is essentially pre-emptive colonic irrigation. I don’t find it that useful, but it obviously fulfils some psychological need.

Now the first of my new categories — exercise. Today’s Ben Jones runs, power-walks or sweats his way through bikram yoga, and he needs to know how well he’s doing. He can wear a pedometer to make sure that he does a certain number of steps every day, and — if the thing is sophisticated enough — how far he has walked. Of course, he may be put off by the calculation that someone once made, that the extra amount of lifespan gained through exercise was likely to be equal to, or less than, the amount of time actually spent in that exercise. In which case the slogan “Live to Run” is a literal truth. But he should take no notice. It makes you feel better — take my word for it. Examine the photographs attached to this piece. Don’t I look radiant? As for the inevitable gibe about the people who died at the fun run in Newcastle this year, all I can say is that they might well have died anyway, doing something far less amusing — such as having sex or completing a bloody Su Doku puzzle.

This thought segues us into the final category, the mind. Or, rather, the not-body. To add to the number of personal trainers out there at the moment, we now have the new profession of life-coaching. A life-coach is someone who advises you on how to break with your bad old time-management habits and take up new, good ones.

This, of course, raises the question of what good and bad life-habits are. In fact, people can generally agree about what constitutes useful behaviour and what is habitual time-wasting. The exception to this consensus, obviously, is watching TV sport. A crude generalisation is that men think it’s time well spent and women don’t.

Most TV is not worth watching. My father told me this when I was 15 and I hated him for it. In those days there were only three channels and it all ended at 11pm. But I now see that he was right, and given that there are currently a zillion channels transmitting 24/7, it’s even truer now that I say it to my hate-filled 15-year-old. There is some stuff that’s OK, but it must be compared with the pap.

Then we have the problem of the computer. I waste vast amounts of time on the PC. My own vice is not porn, partly because I’m scared of my cyber movements being traced by Interpol or the Hampstead & Highgate Express. No, but I do have a weakness for strategy games involving Romans and for obscure centre-left blogging sites where we argue till the cows have come home, lain down and died. Worst of all — and this is a shameful admission — I am addicted to looking myself up on the internet (a) to see what others have said about me, and (b) to see what I’ve said and whether it looks different on the computer screen.

These are my computer vices, but friends of mine have others. They sit there discovering how much houses in their road have been sold for, Googling their neighbours and thinking about buying cars.

If I’m even roughly right about all this, then we might all usefully start to keep a record of what we are doing right and where we are going wrong. Here, to end with, is one I prepared earlier.

Tuesday, November 8.

Run: 6km in 32.15min.
Approx calorie usage: 800.
Walked: 9,700 steps.
8 units fruit and veg. Fish. Four units complex carbs (fine).
1 glass red wine. OK.
Coffee: 3x large soy cappuccino (very bad indeed).
BMI: 25 (lower but still too high).
Waist to hip ratio: 7.8 (very good).
BP: 140 over 75 (not that great — cappuccinos?).
TV: 1hr; Dickens (good), Friends (baddish).
Computer: Porn 0 (good); Barbarian Invasion 1.5 hours (very bad); looking up self 45 minutes (appalling). Trawling Which Treadmill? site 30 minutes (forgivable because found really good running machine).
The Times, Aaronovitch article: 20 minutes (life-changing).

VICE AND VIRTUE IN THE BALANCE

Lionel Shriver, author

I exercise like a fiend and drink like a fish. I don’t eat all day, then eat very well at night. If I’ve been abstemious I feel I have earned the right to indulge.

I tend towards extremes, both in discipline and in self-indulgence. I’m not really a smoker but I have one roll-up a day. I take two drags, then put it out. I’ve been doing that for 20 years.

One thing I’m always disciplined about is exercise. It is my purchase on having control of my life, and if I go a day without exercise, I’ve lost it. Every day I go for a nine-mile run or do callisthenics.

My indulgence hour begins at 10.30pm. I sit down in front of Newsnight with a bowl of popcorn and a glass of sherry, and don’t go to bed until three o’clock. I watch crap TV, spend time with my husband and cook a flash meal. Before that, it’s all privation and discipline.

Simon Gray, playwright

I don’t drink and I don’t like food much. I eat chocolate because I get sugar pangs, which is a consequence of giving up alcohol, but it’s not a vice because I loathe doing it.

Any equilibrium I have was achieved accidentally. I gave up drinking because the alternative was death — it wasn’t about vice or virtue. I smoke 50 or 60 cigarettes a day but I don’t think of that as a vice, either. I don’t exercise, though I do try to walk for 20 minutes a day.

The culture of obsessive healthiness is revolting. When people don’t believe in God, where do their values come from? The inducement becomes to live simply a long life, rather than a good life.

CAN JOGGING DAMAGE YOUR HEALTH?

Jogging improves aerobic fitness, cuts the risk of heart disease and can help to boost bone density. But it is not risk-free.