"Fact or fiction? Sex burns a lot of calories. Snacking or skipping
breakfast is bad. School gym classes make a big difference in 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 Thursday's New England Journal of Medicine says dogma and fallacies are detracting from real solutions to the nation's 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 at
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 of fine print 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 University
professor of nutrition and food studies. "The big issues in weight
loss are how you change the food environment in order for people to
make healthy choices," such as limits on soda sizes and marketing junk
food to children, she said. Some of the myths they cite are "straw men"
issues, she said. But some are pretty interesting. Sex, for
instance. Not that people do it to try to lose weight, but claims that
it burns 100 to 300 calories are common, Allison said. Yet the only
study that scientifically measured the energy output found that sex
lasted six minutes on average ~"disappointing, isn't it?"~ and burned a
mere 21 calories, about as much as walking, he said. That's for a man. The study was done in 1984 and didn't measure the women's experience. Among the other myths or assumptions the authors cite, based on their review of the most rigorous studies on each topic:
—
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 over
the long term. Fact: Although many dieters regain weight, those who
lose a lot to start with often end up at a lower weight than people who
drop more modest amounts.
— Snacking leads to weight gain. Fact: No high quality studies support that, the authors say.
—
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 breastfeeding and eating plenty of fruits
and vegetables, the authors write. And exercise helps prevent a host of
health problems regardless of whether it helps a person shed weight."