This week, the American Medical Association adopted a new policy related to Body Mass Index or BMI, a measurement method that has been used to determine if people are at a healthy weight.
“The new policy supports AMA in educating physicians on the issues with BMI and alternative measures for diagnosing obesity,” said the announcement.
What’s the deal with BMI, and why did the association adopt this new policy? Dr. David Cutler, family medicine physician at Providence Saint John’s Health Center in Santa Monica, Calif., joined KNX to explain.
What is BMI?
“It can be misleading, but it’s an important tool because that’s really the tool that’s being used most pervasively in most medical practices,” said Cutler.
According to a 2015 study published in the Nutrition Today journal, addressing body build as a population-based medical issue gained popularity in the U.S. shortly before 1900.
“Life insurance data accumulated at that time and subsequently indicated that body weight, adjusted for height (Wt/Ht), was an independent determinant of life expectancy, and in 1910, the effects of being overweight were noted to be greater for younger people than for the elderly,” said the study. In 1959, the Metropolitan Life Insurance company published tables of average body weights for heights by gender and age.
Today, the National Heart, Lung and Blood Institute offers a tool for calculating BMI on its website.
“Since it’s simple to measure, most people know what it is,” Cutler explained. “It’s quite frankly, an arithmetic computation of taking your weight, dividing it by your height, and coming up with a number, and the association of that number of being over 25 with being overweight and under 25 as being normal weight has been well ingrained in society now.”
What are the issues with BMI?
Before the AMA adopted the new policy, the AMA Council on Science and Public Health issued a “report which evaluated the problematic history with BMI and explored alternatives,” said the organization.
This report “outlined the harms and benefits of using BMI and pointed to BMI as an imperfect way to measure body fat in multiple groups given that it does not account for differences across race/ethnic groups, sexes, genders, and age-span,” it said. For example, the Harvard T.H. Chan School of Public Health has noted how BMI does not help predict disease risk the same for patients of different ethnicities.
“Under the newly adopted policy, the AMA recognizes issues with using BMI as a measurement due to its historical harm, its use for racist exclusion, and because BMI is based primarily on data collected from previous generations of non-Hispanic white populations,” said the AMA.
“And there are many people who have high BMI who are very healthy,” said Cutler. “And there are some people, obviously, who have lower BMI who aren’t healthy.”
He said that a new, sophisticated X-ray screening tool called DXA is now available and that it is more accurate than a BMI measurement. According to the University of California, Davis, DXA – short for “Dual X-ray Absorptiometry” – is a quick and pain free scan that provides an in-depth analysis of fat tissue, lean mass and bone density.
“When BMI does not agree with that DXA measurement, that creates a little bit of controversy,” Cutler said.
Are doctors dumping BMI altogether?
“Due to significant limitations associated with the widespread use of BMI in clinical settings, the AMA suggests that it be used in conjunction with other valid measures of risk such as, but not limited to, measurements of visceral fat, body adiposity index, body composition, relative fat mass, waist circumference and genetic/metabolic factors,” said the AMA.
However, Cutler noted that BMI calculations are used in his practice all the time. When he goes to the doctor himself, he pays close attention to his.
“I do take heat on it because for me, it’s relevant,” he explained. “My total body composition is not changing very much. So, I know when that number goes up, it’s probably indicating that I have excess body fat and I use diet to try to control that.”
AMA Immediate Past Dr. President Jack Resneck, Jr. also said that physicians may still find appropriate ways to use BMI calculations.
“There are numerous concerns with the way BMI has been used to measure body fat and diagnose obesity, yet some physicians find it to be a helpful measure in certain scenarios,” he said. “It is important for physicians to understand the benefits and limitations of using BMI in clinical settings to determine the best care for their patients.”
When it comes to paying for doctor visits, the AMA said that BMI should not be used as a sole reason to deny appropriate insurance reimbursement for patients.
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