If confirmed, the study could raise serious doubts about the prevailing medical advice to overweight people that they should diet until their weight reduces.
It suggests that the physiological and metabolic stresses associated with weight loss could be so great as to outweigh the benefits of being thinner.
The research, carried out in Finland, followed nearly 20,000 twins over a period of 24 years. Twins are favoured for such studies because the genetic similarities mean the effects of variations in environment or lifestyle can be picked out more easily.
In 1975 they were questioned about their weight and desire to lose weight. The same group was then questioned again in 1981, after which they were monitored for 18 years to see which of them died and from what causes.
Professor Jaakko Kaprio, of Helsinki University’s public health department, who co- authored the research, said the results suggested weight loss by overweight but otherwise healthy people could be “hazardous in the long term”.
“Losing weight seemed to be associated with higher mortality,” said Kaprio. “One reason for this may be that when people diet to lose weight they lose fat-free tissue as well as fat.”
The paper, to be published in a science journal tomorrow, stresses that the findings did not apply to the obese or to overweight people with related conditions such as diabetes.
For such groups the relative benefits of weight loss are likely to be far greater, especially if accompanied by taking more exercise.
The difference between being overweight and obese lies in a person’s body mass index (BMI), which is calculated from weight and height. An adult with a BMI of more than 25 is classed as overweight and one with a BMI of more than 30 is obese.
The researchers cut out data from anyone suffering from diabetes or from other serious illnesses because these often cause weight loss.
This left them with a final sample of 2,957, of whom 268 had died. When the researchers analysed this group they were surprised to find that those who had stuck to their commitment to dieting were more likely to die young than those who stayed fat.
Other studies support the research. In America researchers followed 6,391 middle-aged people, who were either obese or overweight, for nine years and found the lowest mortality among those whose weight remained stable or increased.
Tom Sanders, professor of nutrition at King’s College London, said the impact of the surge in obesity was hard to interpret. “One paradox is that people in the West have grown so much fatter but they are also living longer,” he said. “My view is that there is a big problem with young people becoming overweight. We should be worrying more about them and less about fat middle-aged people who are probably better off staying as they are.”
Around half of British adults are overweight, and 17% of men and 21% of women are obese. Both conditions increase the risk of heart disease, diabetes, osteoarthritis and of several types of cancer.
Pie orgies sadly unlikely to increase lifespan, though
By Lewis Page • Get more from this author
Posted in Biology, 24th June 2009 11:37 GMT
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Cheerful news for those whose Body Mass Index (BMI) falls into the "overweight" range today - you will probably live longer than a person whose BMI is "ideal". Boffins in Canada and America revealed the new findings following a study of over 11,000 Canadians covering the last 12 years.
Unsurprisingly, people whose BMI showed them to be "underweight" or "extremely obese" died sooner than those in the more middle-of the-road brackets. But the medical community's consensus that anyone with a BMI from 25-30 is "overweight", whereas 18.5-25 is "ideal" has been undermined by the fact that survey subjects in the former, heftier band actually lived longer than the lightweights.
"It's not surprising that extreme underweight and extreme obesity increase the risk of dying, but it is surprising that carrying a little extra weight may give people a longevity advantage," said David Feeny, PhD, one of the study's authors.
Among the individuals tracked during the survey, the most dangerous BMI band to be in was "underweight"; next worst was "extremely obese". Both of these groups had significantly increased risks of dying, 70 and 36 per cent above the norm respectively. Those who were merely "obese" and those with an "ideal" BMI ran very similar risks of death. But the "overweight" were actually 17 per cent less likely than normal to die as time went by.
Good news for the moderately swingbellied swivel chair artist up and down the land, then. If you are "overweight" you're actually somewhat less likely to pop your clogs soon than your fellows, and if you've slipped over the line into "obese" you're seemingly no worse off than the smug "ideal" body types.
These results may not come as a surprise to regular readers of Reg medical and health coverage: we've pointed out the obvious tomfoolishness of the Body Mass Index before now, not least the fact that it requires two-dimensional human bodies to work properly.
Portland State University boffin Mark Kaplan, another study author, cautioned that spindly, unhealthy "ideals" shouldn't bust open the pie locker in a rash attempt to jockey themselves into the safety of an "overweight" BMI, however.
"[This research] doesn't mean that people in the normal weight range should try to put on a few pounds," says the scientist.
That makes sense, as BMI's frequently flawed relationship with real humanity probably has more to do with factors such as the increased height of modern Westerners, the way it doesn't differentiate between muscle mass and lard etc. An "ideal" BMI sufferer putting on a few pounds of muscle by doing some judicious exercise might well stave off death for a bit longer; simply gorging on cakes probably won't help.
Still, at least TV food comic Giles Coren's recent calls for a BMI tax are now further exposed as foolishness, and the "fat people" that he rashly proposes to attack with a stick (any time, Coren - better make it a big stick*) have the consolation of knowing that they'll probably outlive him. ®
*Your correspondent is 6'3" and 16 stone, i.e. "overweight".
Thank you, I knew I wasn't crazy.
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