I have never seen someone who was previously fat become forever thin. Some dieters get down for a while but it always goes back up. The only person I know who used to be fat but became permanently thin is someone who had severe cancer and had half their intestines removed. Not exactly the way you want to do 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.
They followed 5,362 men and women from their birth in 1946 and 20,000 from birth in 1958, measuring their weight and blood pressure and assessing their lifestyles.
The researchers found both groups began gaining weight in the 1980s and have steadily increased in size ever since.
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," she added.
I wonder about preventative measures being important too, because it seems once the fat is there, it's far harder to get rid of. Also why aren't the scientists paying attention to the fact of lower metabolism among fat people? Metabolism is the ignored elephant in the room.