19/02/2014 16:41 GMT | Updated 21/04/2014 06:59 BST

Whoops! There's Goes That Weight Loss Willpower Yet Again

I don't want to be a killjoy, but did you know that research shows the middle of February is when most women ditch their new year diet because they can't hack it any more? It's about now when weight loss willpower turns into won't-power and all our resolutions go to pot.

It's estimated that 15million Britons are on a diet at any one time. That's one person in four! A recent Mintel survey showed that 29million Britons tried to lose weight last year.

Funny how so many of us diet year after year even though we know deep down inside that any weight we lose will go back on again as soon as we stop.

I've been advising people for a long time that yo-yo diets are not the way to lose weight and keep it off in the long term - the average woman in Britain spends 31 years dieting in her lifetime and loses the same 30lbs about nine times.

That's more than a third of your life doing something that's agonising, demoralising and possibly harmful. Losing weight permanently requires a lifestyle change - a retuning of your mindset that nudges you towards a new relationship with food and exercise - so that you automatically eat less and make healthier choices without even having to think about it.

Here's five scientifically-proven things you should know about why diets fail in the long term.

ONE: Cutting out calories changes your metabolism and your brain so your body hoards fat and turns minor food cravings into an obsession. Research at Melbourne University proves that when you go on a starvation diet the body produces about 20% more of the appetite stimulating hormone ghrelin, forcing you to overeat once the diet stops.

TWO: Because of the way the metabolism changes during dieting, you need to eat 400 fewer calories a day than before you were dieting just to maintain a stable weight. But the powerful appetite stimulator makes this almost impossible to achieve. And studies at Columbia University in America say this yo-yo situation can last as long as six years.

THREE: Diets change the way the brain reacts to food in a negative way, wilting your willpower. Brain scans carried out by American neuroscientists show dieters display an increase in emotional responses to food and a decrease in brain activity linked to restraint.

FOUR: Within five years, about two-thirds of dieters put back all the weight they have lost - and more. The University of California has found that slimmers lose up to 10% of their body weight in six months on most diets. But an analysis of 31 long-term clinical studies shows that most of the dieters would have been better off not dieting because their weight would have been pretty much the same and their bodies would not have wear and tear caused by the yo-yo syndrome.

FIVE: The younger you start dieting the worse the effects on your body. People who start dieting habitually in their teens tend to be significantly heavier after five years than teens who never dieted, says research published in the medical journal American Psychologist. Once we become overweight, most of us will stay that way if all we do is diet.

So diets don't work except in the short term. I spoke to a lovely lady who told me she had "successfully done the Atkins diet." When I asked her if she'd managed to keep off the weight she'd lost, she admitted she'd put it all back on again.

Is that the definition of success - you lose weight and put it back on again? Sadly, for the overwhelming majority of slimmers it is.

For them the diet "works" because it helps them lose maybe 10lbs in a month. When the weight inevitably goes back on again they don't consider the diet hasn't worked - they believe it is themselves who have failed.

The low esteem this diet-fail-diet-fail cycle can produce often has just one effect - reach for the cakes and the chocolates for some comfort eating. And bang goes the waistline again.

Isn't it time to do something different? If only because you deserve a better way to lose weight.