Sex to burn fat? It may be a myth

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scale lib sxc.hu 'Though obesity is a serious risk factor for conditions such as heart disease, some slim people can have a genetic susceptibility that makes them vulnerable too.'

Fact or fiction? Sex burns a lot of calories. Snacking or skipping breakfast is bad. School gym classes make a big difference to kids’ weight.

All are myths or at least presumptions that may not be true, say researchers who reviewed the science behind some widely held obesity beliefs and found it lacking.

Their report in the New England Journal of Medicine says dogma and fallacies are detracting from real solutions to weight problems.

“The evidence is what matters, and many feel-good ideas repeated by well-meaning health experts just don’t have it,” said the lead author, David Allison, a biostatistician at the University of Alabama in Birmingham.

Independent researchers say the authors have some valid points.

But many of the report’s authors also have deep financial ties to food, beverage and weight-loss product makers – the disclosures take up half a page in the journal.

“It raises questions about what the purpose of this paper is and whether it’s aimed at promoting drugs, meal replacement products and bariatric surgery as solutions,” said Marion Nestle, a New York professor of nutrition and food studies.

“The big issues in weight loss are how you change the food environment for people to make healthy choices, such as limits on soda sizes and marketing junk food to children.”

Some of the myths they cite are “straw men” issues, she said.

But some are interesting. Sex, for instance. Not that people do it to lose weight, but claims that it burned 100 to 300 calories were common, said Allison.

However, the only study that scientifically measured the energy output found that sex lasted six minutes on average – and burnt a mere 21 calories – just as much as walking for men. The study was done in 1984 and didn’t measure the women’s experience.

Among the other myths or assumptions the authors cite:

* Small changes in diet or exercise lead to large, long-term weight changes. Fact: The body adapts to changes, so small steps to cut calories don’t have the same effect over time, studies suggest. At least one outside expert agrees with the authors that the “small changes” concept is based on an “oversimplified” 3,500-calorie rule, that adding or cutting that many calories alters weight by one pound.

* School gym classes have a big impact on kids’ weight. Fact: Classes typically are not long, often or intense enough to make much difference .

* Losing a lot of weight quickly is worse than losing a little slowly. Fact: Although many dieters regain weight, those who lose a lot to start with often end up at a lower weight than those who drop modest amounts.

* Snacking leads to weight gain. Fact: No high-quality studies support this contention.

* Regularly eating breakfast helps prevent obesity. Fact: Two studies found no effect on weight and one suggested that the effect depended on whether people were used to skipping breakfast or not.

* Setting overly ambitious goals leads to frustration and less weight loss. Fact: Some studies suggest people do better with high goals.

Some things may not have the strongest evidence for preventing obesity, but are good for other reasons, such as breast-feeding and eating plenty of fruits and vegetables, the authors write.

And exercise helps prevent health problems regardless of whether it helps one shed weight.

“I agree with most of the points except the authors’ conclusions that meal replacement products and diet drugs work for battling obesity,” said Dr David Ludwig of Boston Children’s Hospital. – Sapa-AP

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