It's bad enough that women the world over are taught to believe that anyone larger than size 0 is undisciplined and lazy, but, according to Kunis, we can add ''liar'' to the list of character flaws. Fast forward eight months, and Kunis has changed her tune. In the April edition of Harper's Bazaar she lets slip that not only has she regained the weight she lost on her way to becoming a swan, but her body has changed shape, and not in a good way. ''When I gained it back, it went to completely different areas. Not my rear … I'd be happy if my arse got bigger. All the weight that left my chest went to my side hip, my stomach.'' Kunis' belated realisation that diets don't work will not surprise the average woman who spends 31 years of her life trying to lose weight.

It also won't surprise anyone acquainted with weight loss science. More than 50 years of research confirms that diets have a failure rate of between 95 to 98 per cent. That's right - of every 100 people who diet, 98 of them will either lose no weight or will soon regain any weight they do lose. According to the US National Institute of Health technology assessment conference, ''[weight-loss] interventions produce short-term losses followed by weight regain, and no current treatments appear capable of producing permanent weight loss''. Not a single diet or weight-loss treatment works. Not one. And that doesn't apply just to extreme fad diets that come and go as quickly as a bread roll to a carb-starved ex-Dukan Dieter. What decades of research tells us is that diets do not work. Full stop. Worse, Columbia University researchers suggest that our bodies may burn fewer calories than normal for as many as six years after we diet because the metabolisms of people who have lost weight through dieting are slower than people of the same weight who did not diet. Imagine that your friend is naturally a size 10 and you're a size 12. You may be able to diet to get down to the same weight as your friend, but once you're there you cannot eat what she eats.

If you eat the same number of calories as your non-dieting friend, you will most likely gain weight and she won't. That's because you've screwed up your metabolism for six years - possibly longer - and your friend's metabolism is still operating normally. This is your reward for the joy-sapping, soul-destroying, life-consuming deprivation of dieting. Worse still, you will regain more weight than you started out with. Melbourne University professor Joseph Proietto, head of the weight control clinic at Austin Health, has found that dieters' bodies behave like they are starving, still trying to regain the lost weight a full 12 months after the diet has ended. Participants in a study published last year in the New England Journal of Medicine reported feeling hungrier and more preoccupied with food than before they lost weight. This is not surprising because the researchers found that the levels of ghrelin, the hormone that makes us feel hungry, was about 20 per cent higher than at the start of the study and that the hormones that suppress hunger and stimulate metabolism were abnormally low. "What we see here is a co-ordinated defence mechanism with multiple components all directed towards making us put on weight," Proietto says. "This, I think, explains the high failure rate in obesity treatment." And if you don't believe the scientists, then just look to our celebrity experts such as Mila Kunis. By her own admission, dieting has permanently changed her body. With such a high failure rate, it's time to stop perpetuating the lie that losing weight is just about wanting it enough. Because it's not us who have failed. It's the diets. And every time a smug skinny mini makes a catty comment in the press, she fails us all.

Kasey Edwards is the author of Thirty-Something and the Clock is Ticking. Follow the National Times on Twitter: @NationalTimesAU