04/03/2012 15:37 GMT | Updated 04/05/2012 06:12 BST

Why Ruth Jones Only Has a 2% Chance of Staying Thin

Ruth Jones is the latest celebrity weight loss sensation. She joins Dawn French, Nigella Lawson and Pauline Quirk in the list of big girls who have very publicly gone from being 'happy in their skin' to drastically dropping the pounds, appearing in glamorous gowns showing off their new look. Each of them telling the story of how they did it, ranging from drastic liquid diets (Pauline Quirk) to 'sensible' calorie counting (Ruth Jones).

Their weight is their business, of course, but they are setting themselves up for a fall by talking about how they've done it - or by talking about it at all. Just like the vast majority of the celebrity weight losses before them (Oprah Winfrey, Natalie Cassidy, Kirstie Alley, etc) they only have a two per cent chance of keeping the weight off in the long term.

I'm not trying to p*ss on their parade - far from it. I'm trying to throw some rational thinking into the mix. And because I'm being rational I'm going to change that sentence about chances of success to a more sensible way of putting it, removing the emphasis from a side effect to the real problem:

These women only have a two per cent chance of maintaining in the long term the uncomfortable struggle against the overwhelming compulsion to overeat

If you understand anything about dieting (chances are you don't), you'll know about the balance of motivations. As long as weight loss is causing enough excitement, control over food is possible. And if you're getting loads of media attention (or attention from friends if you're not a celeb) over your weight loss and you're getting a buzz from it, then the excitement will make counting calories (or rejecting food for a dodgy meat flavoured milk shake) relatively easy. The weight loss is more important than the food. But because your brain is designed to require novelty and to slowly dampen down experiences that you have regularly, the buzz from the attention and approval is going to need to be increased for you to get the same hit from it.

This is all part of the survival mechanism. It's how the human race progresses. The woman who invented the wheel was probably very excited about rolling it around the ground. What fun it would have been when she only previously had boring old straight-edged rocks to push. If she hadn't finally got bored with the wheel - if her brain hadn't dampened down the excitement of it - she would never have been motivated enough to invent the cart. We'd all still be rolling rocks around the floor, laughing our heads off.

But your brain does dampen down your thrill at other people's reactions to your weight loss. And the media (and your friends) get bored of it and they stop talking about it. So just at the time when you need more admiration for looking good, you get less. Suddenly, you find yourself feeling a bit down and you can't explain why. You can't get excited about your weight loss any more. Your life has gone back to normal - you're just thinner.

So now you're faced with a cake. You know you shouldn't eat it. You argue with yourself. You then find you've eaten it. You feel guilty. You think: "I'll get back on my diet tomorrow." So you eat for the rest of the day.

The next day you're determined to get back on track. But you just can't get the feeling back. Then your husband says: "Let's get a Chinese." You think: "Oh, well, it's only one more day."

I think you know the rest.

What has happened, although you don't realise it, is after so long living with the weight loss being more exciting than the food, now the food has become more exciting than the weight loss. When food is more exciting than weight loss, which do you think is the winner in a battle against cake?

This is why celebrities, such as Oprah, Kirstie and Natalie, live to regret their public announcements about their weight loss and why they end up feeling a great deal of pressure to fight a battle they're swiftly and cruelly losing.

But this is a process that affects all of us. You don't have to be a celebrity to fall into this trap. But the celebration of temporary celebrity weight loss and the lure of the buzz and approval is exactly what snares us all into dieting.

Dieting doesn't work.

So celebrities, especially yo-yo dieting celebrities should refuse to talk about their weight loss for at least five years. For their own sake and for yours.

Read more in my bookEat Less Without Trying To Eat Less. And get a FREE chapter here.