why are bmi charts not always accurate?
People who seek medical treatment for obesity or an eating disorder do so in the
hope that their health plan will pay for part of the treatment. But if it is covered up,
it often comes down to a measure invented nearly 200 years ago by a Belgian
mathematician as part of his quest to use statistics to define the "average man."
That work, done in the 1830s by Adolphe Quetelet, attracted life insurance
companies, which created "ideal" weight charts after the turn of the century.
In the 1970s and 1980s, the measure, now called body mass index, was adopted
to detect and track obesity.
Now it's everywhere, using an equation, essentially a relationship between mass
and height, to categorize patients as overweight, underweight, or at a "healthy
weight." It's delightfully simple, with a scale that designates adults with scores
between 18.5 and 24.9 within a healthy range.
READ MORE: To improve patient care, doctors are rethinking
long-standing biases around obesity.
But critics—and they're widespread these days—say it was never intended as a
health diagnostic tool. "BMI doesn't come from science or medicine," said Dr.
Fatima Stanford, a specialist in obesity medicine and director of equity for the
division of endocrinology at Massachusetts General Hospital.
She and other experts said BMI can be useful for tracking population-wide
weight trends, but it falls short by not accounting for differences between
ethnic groups, and may target some people, including athletes, as obese or
overweight because it does not distinguish between muscle mass and fat.
Still, BMI has become a standard tool for determining who is most at risk for the
health consequences of excess weight and who qualifies for often-expensive
treatments. Despite the intense debate surrounding BMI, the consensus is that
people who are overweight or obese are at higher risk for a number of health
problems, including diabetes, liver problems, osteoarthritis, high blood pressure,
sleep apnea, and heart problems cardiovascular.
The BMI measurement is commonly included in prescription instructions for
weight-loss medications. Some of the newer, more effective drugs, like Wegovy,
limit use to patients who have a BMI of 30 or higher (the obesity threshold) or
below 27, if the patient has at least one obesity-related medical condition.
The weight, like diabetes. Doctors can prescribe the drugs to patients who
don't meet the label requirements, but insurers may not cover any of the costs.
While most insurers, including Medicare, cover some forms of bariatric
weight-loss surgery, they may require the patient to have a BMI of at least 35,
along with other medical conditions, such as high blood pressure or diabetes,
to qualify.
With medications, it can be even more complicated. Medicare, for example,
doesn't cover most prescription weight-loss drugs, though it will cover behavioral
health treatments and obesity screening. Weight-loss drug coverage varies
among private health plans.
"It's very frustrating because everything we do in obesity medicine is based on
these limits," Stanford said.
Critics say BMI can err on both ends of the scale, mislabeling some larger people
as unhealthy and people who weigh less than healthy, even if they need
medical treatment.
For eating disorders, insurers often use BMI to make coverage decisions and may
limit treatment to only those who are classified as underweight, leaving out others
who need help, said Serena Nangia, director of communications for Project Heal,
a nonprofit organization that helps patients get treatment whether they are
uninsured or have been denied care through their health plan.
"Because there's so much focus on BMI numbers, we're missing people who
could have gotten help earlier, even if they have a medium BMI," Nangia said.
"If they are not underweight, they are not taken seriously and their behaviors are
overlooked."
"Stanford" said: "she also often fights with insurance companies over who
qualifies for overweight treatment based on BMI definitions, especially some of
the newer and more expensive weight-loss drugs, which can cost more than
$1,500 a month."
"I've had patients do well on medication, and their BMI is below a certain level,
and then the insurance company wants to take them off medication," Stanford
said, adding that she challenges those decisions. "Sometimes I win,
sometimes I lose."
Although it may be useful as a screening tool, BMI alone is not a good arbiter of
health, Stanford and many other experts say.
"A person with a BMI of 29 could be in worse health than a person with a BMI
of 50 if that person with a BMI of 29 has high cholesterol, diabetes, sleep apnea,
or a long list of things," Stanford said, "whereas the person with a BMI of 50 only
has high blood pressure. Which one is sicker? "I would say the person with the
most metabolic diseases."
Also, BMI can overestimate obesity in tall people and underestimate it in short
people, experts say. And it does not take into account ethnic and gender
differences.
Case in point: "Black women who have a BMI between 31 and 33 tend to be in
better health even at that level above 30" than other women and men, Stanford
said.
Meanwhile, several studies, including the Long-Term Nurses' Health Study,
found that Asian people had a higher risk of developing diabetes as they gained
weight, compared to whites and certain ethnic groups. As a result, countries
such as China and Japan have set lower BMI overweight and obesity thresholds
for people of Asian descent.
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system:The AP-NORC survey is
Experts generally agree that BMI should not be the only measure for evaluating
patients' health and weight.
"It has limitations," said David Creel, a psychologist and registered dietitian at
the Cleveland Clinic Metabolic and Bariatric Institute. "It doesn't tell us anything
about the difference between muscle weight and fat weight," he said, noting that
many athletes could score in the overweight category, or even fall into the obese
range because of their muscular mass.
Instead of relying on BMI, doctors and patients need to consider other factors in
the weight equation. One is to be aware of where the weight is distributed.
Studies have shown that health risks increase if a person has excess weight in
the midsection. "If someone has thick legs and most of their weight is in their
lower body, it's not as damaging as having it around their waist, especially to
their organs," Creel said.
Stanford agrees, saying midsection weight "is a much better indicator of health
than BMI itself," with the potential for conditions like fatty liver disease or
diabetes "directly correlated with the waist."
Patients and their doctors can use a simple tool to assess this risk: the tape
measure. Measuring just above the hip bone, women should stay at 35 inches or
fewer; men should stay at 40 inches or fewer, the researchers advise.
New ways to define and diagnose obesity are in the works, including a panel of
international experts convened by the prestigious Lancet Commission, said
Stanford, a member of the group. Any new criteria that ultimately pass could not
only help inform doctors and patients, but also affect insurance coverage and
public health interventions.
Stanford has also studied a way to recalibrate BMI to reflect ethnic and gender
differences. It incorporates risk factors from various groups for conditions such
as diabetes, high blood pressure, and high cholesterol.
Based on his research, he said, the BMI cutoff would tend to be lower for men,
as well as for Hispanic and white women. I would switch to slightly higher limits
for black women. (Hispanics can be of any race or combination of races.)
"We don't plan to eliminate BMI, but we do plan to devise other strategies to
assess health associated with weight status," Stanford said. More studies are
needed on this subject.
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