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Since 1st March, 1999
 
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Shot of diet control

London, Dec. 2: Scientists believe that they have discovered a cure to yo-yo dieting, the nightmare that afflicts 85 per cent of dieters, who lose weight only to put it straight back on again.

Almost everybody can lose weight, for a while, using a wide range of diets. So long as calories consumed are fewer than calories expended, they will lose weight.

Some overweight people go through decades of yo-yo dieting, never getting control of their weight and damaging their health by the constant fluctuations.

Now a team from Columbia University in New York has found that injections of the naturally occurring hormone, leptin, can persuade the body that it does not need to eat more to conserve its fat levels.

“Obesity is a very unusual condition as the body fights against the cure,” said Michael Rosenbaum, the team leader. “With most conditions, as you recover you get better off. But with obesity, as you lose weight the body says it doesn’t like it. That puts you in an abnormal status, and the weight loss can’t be sustained.”

In experiments on 10 volunteers, the team has found a way of stopping the process. In people who have recently lost weight, injections of leptin prevent the physiological response that encourages them to put it back on again. These responses have nothing to do with greed, or lack of willpower. They probably derive from early human history, when periods of famine alternated with successful hunts that produced a feast.

Leptin is produced by fat cells, and its role is to signal to the brain about the level of fat stores in the body. Its deficiency implies fat stores are running low, encouraging eating.

When it was first discovered a decade ago, there were hopes that it would provide a magic fat cure. These have largely been disappointed. There are a few families who lack the gene for leptin and grow abnormally fat, and in these rare cases, injections of leptin help them to lose weight.

But in the vast majority of people, leptin levels can be raised tenfold without perceptible effect. The research, published in the Journal of Clinical Investigation, used it in a different way. It was injected into people who had already lost weight hoping it might prevent them from putting it on again. This time it worked.

These were physiological tests, not clinical trials. In practice, daily injections are not very practical. A more likely route, Rosenbaum said, would be to devise a drug that would interfere with the leptin pathway and get the same effect.

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