Once you're fat, you never go back: Scientists say dieters' bodies rarely return to their former shape

By Tamara Cohen

Last updated at 8:57 AM on 25th July 2011

Dieting: It will increase fitness and lower blood pressure but ultimately not lead to weight loss

It is what failed dieters have long suspected: fat people really can't keep the weight off.

Scientists have confirmed that the majority of overweight people who try to lose weight either by cutting calories or exercising will return to their former size.

Fewer than 10 per cent of the 12million Britons who go on a diet each year succeed in losing significant amounts of weight and most of those who do put it all back on again within a year.

The study of 25,000 people provides further evidence of the prevalence of ‘yo-yo dieting’ where slimmers get into a cycle of losing weight and regaining it.

The scientists, from the Medical Research Council’s National Survey of Health and Development, have concluded it is better to avoid getting fat in the first place.

Dr Rebecca Hardy, the council’s programme leader on body size, said: ‘Once people become overweight, they continue relentlessly upwards. They hardly ever go back down.

‘A few lose weight but very few get back to normal. The best policy is to prevent people becoming overweight.

‘For men [weight] goes up steadily through life. For women it starts slowly and accelerates in the mid-thirties.’

But the study’s findings do not mean dieting is pointless, as eating less and taking more exercise can increase fitness and lower blood pressure.

In 2009, a quarter of adults and 14 per cent of children were obese, according to the Department of Health’s latest Health Survey for England.

Although previous research has shown one in four Britons is trying to lose weight at any one time, it has been predicted that 60 per cent of us will be obese by 2050, leading to even more cases of diabetes, heart disease and cancer.

Experts have suggested evolution means we are programmed to put on weight rather than lose it. Dieting can make this tendency worse as decreasing calorie intake triggers the body to go into starvation mode and reduce the amount of energy it naturally expends, making it even harder to lose weight.

Commenting on the study, Professor Nick Finer, an endocrinologist at University College London Hospital, said: ‘It is unlikely that man would have evolved with mechanisms to counter obesity which has only become a problem in the last 30-40 years.

'For most of human history, storing fat would have been an advantage.’