(HealthDayNews) -- A new study
involving obese individuals suggests the reason the
Atkins, Zone and other low-carb regimens help people
lose weight is that dieters don't substitute fatty or
sugary foods for the carbohydrates they lack.
Instead, they simply eat less food.
"Take the carbohydrates away, and I expected the
participants would just eat more of the other stuff,"
said researcher Dr. Guenther Boden, a professor of biochemistry
at Temple University, in Philadelphia.
"But they didn't. In fact, it turned out they
ate 1,000 calories less every day," he said.
The findings, published in the March 15 issue of the
Annals of Internal Medicine, may help allay concerns
these diets raise heart risks linked to increased fat
According to Boden, numerous theories have been floated
as to how low-carbohydrate diets trigger weight loss.
"The possibilities were: People eat less, they
expend more calories, they don't really lose body mass
but instead they lose water, and a fourth possibility
-- very popularly expressed -- that carbohydrate calories
are somehow different from other calories," he
To help determine the correct answer, his team sequestered
10 obese patients, all diagnosed with type 2 diabetes,
in a controlled, clinical environment where diets were
strictly monitored for three weeks. Boden's team also
used the very latest technology to assess weight-related
outcomes such as body mass loss, water loss, and total
For the first week, participants ate their usual mixed
diet. But during the last two weeks the researchers
restricted their intake of carbohydrates from an average
of 300 grams per day to just 20 grams a day.
At the same time, a tempting array of fatty, sugary
and other foods was readily available to all.
"We told them 'Look, you can eat as much of anything
else as you want, whenever you want,' " Boden said.
The result: By the end of the two-week low-carb regimen,
patients lost an average of 1.65 kilograms (3.6 pounds)
and reduced their daily caloric intake by nearly 1,000
calories -- from an average of 3,111 calories before
they began the diet, to just 2,164 calories while on
the low-carb regimen.
"In other words, they self-corrected their previously
excessive appetites down to normal," Boden said.
And that magic number of around 2,100 calories per
day "turned out to be exactly the amount of energy
they should've been consuming to start with" to
avoid weight gain, he added.
As happens naturally with weight loss, diabetes risk
factors such as insulin and blood-glucose levels began
to noticeably improve. So did levels of unhealthy blood
fats called triglycerides -- a finding noted in previous
studies that looked at the effects of low-carb diets
on cardiovascular health.
The study, which was funded by grants from the National
Institutes of Health and the American Diabetes Association,
still leaves unanswered the question of why carb-deprived
individuals don't reach for sugars, proteins or fats.
"The only thing that makes sense to me is a drop
in insulin," Boden said. "I've been treating
diabetics for decades, and every time I start them on
insulin they gain weight. So I am sure insulin has something
to do with appetite."
"I can't prove it, of course," he added,
"Because we still know so very little about appetite.
Everyone's on thin ice there."
Dietitian Cathy Nonas is director of the obesity and
diabetes program at North General Hospital, in New York
City, and a spokeswoman for the American Dietetic Association.
She said the study doesn't tell scientists much they
didn't already know about low-carb diets.
"If you look at all of the Atkins data that's
ever been done, including USDA White Papers and so forth,
people lose weight on the Atkins diet because they eat
lower amounts of calories," she said. "And
that's true of most diets."
And Nonas said previous studies have suggested that
cutting back on one type of food doesn't necessarily
mean people are going to gorge on another.
She's also concerned that the Temple study didn't include
a control group -- participants the researchers could
have used for comparison purposes.
"The problem here," she said, "is that
we don't have a study where you also looked at taking
away meat, for example -- would we have seen similar,
greater, or less change in weight?"
But another expert believes the new study "adds
to the literature suggesting that low-carbohydrate diets
may have a place in the treatment of obesity."
In his editorial comment, Dr. George A. Bray, of the
Pennington Biomedical Research Center, in Baton Rouge,
La., called the Temple research "nicely done."
Long-term studies focused on the Atkins diet have found
short-term weight loss that often exceeds that seen
in other diets, Bray writes, "but the differences
vanished after 12 months." He believes low-carb
regimens should be simply added to a growing list of
relatively safe weight-loss options for America's overweight
Nonas remains skeptical that any diet that excludes
a whole food group can be healthy -- or sustainable
-- over the very long term, however. And she believes
Americans need only look abroad to find an ideal dietary
model for life.
"All of the societies with low levels of the kinds
of diseases [that plague us] have diets with lots of
vegetables and fruits, a small amount of whole grains,
portion-control, and a much higher fiber intake,"
she said. "And fiber isn't something that's been
high on the list in any of these studies."
For lots more on diet and nutrition, head to the American
By E.J. Mundell
SOURCES: Guenther Boden, M.D., program director, General
Clinical Research Center, Temple University School of
Medicine, Philadelphia; Cathy Nonas, M.S., R.D., C.D.E.,
director, obesity and diabetes program, North General
Hospital, New York City, and spokeswoman, American Dietetic
Association; March 15, 2005, Annals of Internal Medicine
Last Updated: January 2006
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