BMI Is Not A Good Measure Of Our Health. How Else Should We Evaluate It?
The AMA recently acknowledged that the use of BMI has caused "historical harm," and released a new policy on how to better measure our health.
For years, both laypeople and health experts have been suggesting that body mass index (BMI) isn’t an accurate measurement of a person’s health. Now, the American Medical Association (AMA) has finally gotten on board, adopting a “new policy recognizing the issues with using BMI as a measurement.”
BMI, which is a person’s weight divided by the square of their height, is often used by doctors as a “simple, inexpensive and noninvasive surrogate measure of body fat,” according to the Centers for Disease Control and Prevention (CDC). BMI doesn’t directly measure body fat because muscle and bone weigh differently than fat, and BMI doesn’t take into account a person’s muscle mass or bone density, which makes it an imprecise measure of body fat.
In a press release on the new report, the AMA Council on Science and Public Health stated that BMI shouldn’t be considered a standalone measure of health because of limitations in its calculation, citing the “historical harm of BMI, the use of BMI for racist exclusion, and BMI cutoffs being based primarily on data collected on previous generations of non-white Hispanic populations that don’t consider gender.”
Although BMI isn’t a totally useless measure of health, its importance may be overinflated in doctors’ offices. BMI cutoffs for what is considered underweight, ideal, overweight, and obese are calculated based on measurements taken only from non-Hispanic white men. The metric does not take age, sex/gender, or race into consideration, which has proven harmful to women and people of color over the years.
“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,” said AMA Immediate Past President Jack Resneck, M.D.
However, there’s a lot that goes into interpreting a person’s BMI — and you can’t just take that number at face value. “Numerous comorbidities, lifestyle issues, gender, ethnicities, medically significant familial-determined mortality effectors, duration of time one spends in certain BMI categories and the expected accumulation of fat with aging are likely to significantly affect interpretation of BMI data, particularly in regard to morbidity and mortality rates,” according to the press release.
The release also explicitly called on insurance companies to disallow the use of BMI as the “sole criterion to deny appropriate insurance reimbursement.”
But if BMI is out, how should we measure our health in relation to our weight? Does weight even matter? And what’s the most reliable metric of our overall health?
Ultimately, the AMA suggests that BMI should be used in clinical settings, but not as a measure of health alone. Instead, they recommend using ”other valid measures of risk” such as visceral fat, body composition, relative fat mass, waist circumference, and more.
The release notes that BMI is correlated with fat mass, but it “loses predictability when applied on the individual level.” That means that although it is useful as a factor when, say, looking at the metabolic health of all people with a certain BMI, it doesn’t say much about the metabolic health of an individual person with that BMI.
So how should you consider your own health with this new perspective on BMI?
Think about your lifestyle. Any exercise — from desk biking while you work to super-intense CrossFit training — is beneficial exercise. Studies have shown that even short walks improve cardiovascular health and increase longevity, and occasional weightlifting has been linked to better overall health than cardio training alone. It’s important to remember that fitness isn’t about getting ripped at the gym; it’s about healthy lifestyle choices. It may also help to remember that bodies change with age and circumstance. A 40-year-old man should have different fitness goals than a 20-year-old man.
The bottom line is that a number on a scale (divided by the square of your height) doesn’t determine your overall health. Bodies and body compositions are different from person to person and across demographics. Instead of obsessing over the numbers, think of fitness as a lifestyle and understand that even small choices and changes can mean significant benefits to your health.