MONDAY, April 2 (HealthDay News) -- The way that obesity is
currently measured greatly underestimates the actual number of
women who are obese, a new study suggests.
Almost half of women currently labeled as not obese by virtue of
their body mass index (BMI) turned out to be obese when measured by
a newer method focusing on their percentage of body fat by weight,
the research found.
Researchers Dr. Eric Braverman, president of the Path Foundation
in New York City, and Dr. Nirav Shah, the current New York state
health commissioner, say that an accurate measurement of obesity
should include percentage of body fat as well as the ratio of
height and weight known as BMI.
"If you're counting on looking at your body fat based on body mass index, it's virtually completely unreliable," Braverman said.
Based on BMI alone, "roughly 30 percent of Americans are obese,
but when you use other methods, closer to 60 percent are obese," he
said. "We call BMI the 'baloney mass index,'" Braverman noted.
"We are fatter than we realize; it's the percent of body fat, not BMI, that makes you obese," he explained.
The problem is especially seen among women, because "as women
age, they tend to lose bone and replace muscle with fat," Braverman
The report was published online April 2 in the journal
Braverman and Shah found that when women had a special scan
called a dual-energy X-ray absorptiometry (DEXA) scan, which
measures body fat, muscle mass and bone density, obesity measured
by BMI alone underestimated obesity.
Among the more than 1,300 people who underwent DEXA in the
study, almost half of women (48 percent) were misclassified as not
obese by BMI, but were found to be obese by percent body fat on
In contrast, 25 percent of men were misclassified as being obese
by BMI, but were in fact
not obese by percent body fat.
In fact, the researchers said, all of the study participants who
were found to be obese by DEXA were women.
Braverman noted that a DEXA scan is expensive, so it wouldn't be
practical for routine assessment. However, a simple blood test that
measures leptin levels can serve the same purpose, he said. Leptin
is a hormone involved in regulating appetite and metabolism.
In the study, levels of leptin correlated to body fat. The
researchers said leptin levels can be used along with BMI as a more
accurate measure of obesity.
"Leptin is a better marker of obesity in women," Braverman stressed, adding that successful weight loss depends on lowering leptin levels. However, he said, women can develop leptin resistance -- a metabolic disorder most often seen after menopause -- which makes dieting ineffective.
People with leptin levels below 5 nanograms per milliliter
(ng/mL) are considered thin and levels up to 10 are considered
normal weight. Leptin levels of 10 to 30 ng/mL are correctable
through diet and exercise, Braverman said, but extremely high
levels are hard to reduce.
The effect of leptin is not as powerful in men, he said. But men
with low leptin levels are very fit, he added.
Braverman believes that, eventually, leptin tests will become a
regular part of a physical exam and people with high levels will be
treated with various drugs and diets designed to reduce leptin
"Everyone is going to get a leptin level [reading] just as they do cholesterol [level reading] today," he said.
Commenting on the study, Dr. William O'Neill, a professor of
cardiology and executive dean for research at the University of
Miami Miller School of Medicine, said that "it's a little bit
"Traditionally we have used BMI. But this study tells you BMI is relatively accurate for men, but for women it really underestimates how many women are obese," he said.
There aren't a lot of data yet on the health benefits of
lowering leptin, O'Neill pointed out. "We will have to see if
elevated leptin levels are a cause of a bad outcome. This hasn't
been done yet," he noted.
"It certainly sensitizes me to the possibility that ordering leptin levels in women who might be obese may be worthwhile," O'Neill added.
Whether lowering leptin levels alone will reduce obesity isn't
known. "We don't know if leptin can be a primary target -- it may
just be a marker of body fat," he suggested.
But people with high leptin levels should lose weight, O'Neill
For more on obesity, visit the
U.S. National Library of Medicine.
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