The problem with BMI: Why this simple system for measuring obesity is so controversial

Watch the CBS Experiences documentary, “Talking Frankly | Fats Shaming,” within the video participant above.


It is a easy little instrument that is been utilized by medical doctors for many years, however the system of measuring Physique Mass Index, or BMI, is more and more coming underneath hearth. Critics have denounced BMI as not simply unreliable however sexist and racistand even many clinicians who see worth in it additionally acknowledge its flaws.

BMI is a components that makes use of an individual’s peak and weight ratio to evaluate whether or not they’re underweight, regular weight, obese or overweight, though it’s not a direct measure of physique fats. First invented almost 200 years in the past by the Belgian mathematician, astronomer and statistician Adolphe Quetelet, it was initially referred to as the Quetelet Index till American physiologist Ancel Keys got here up with the time period Physique Mass Index in 1972.

In keeping with the Facilities for Illness Management and Prevention, BMI is an “cheap and simple screening methodology” that’s “strongly correlated” with weight-related medical situations — severe well being issues together with coronary heart illnessstroke, kind 2 diabetes, sleep apnea and respiration issues, and quite a few varieties of most cancers, About 40% of US adults are thought of overweight,

However lately, medical doctors, scientists and dietitians have expressed issues over the shortcomings of BMI. Although it is used to diagnose weight problems — outlined as having a BMI of 30 or above — it doesn’t present any details about how weight really impacts a person’s well being.

“The issue with the BMI, whereas it does regulate for peak, it doesn’t regulate for what makes up the load,” mentioned Dr. David Katz, an professional in preventive medication and founding director of the Yale-Griffin Prevention Analysis Heart. “So anyone who’s extraordinarily muscular might have a excessive BMI and but have a really low % physique fats, which is what you are actually involved with. Any individual who has little or no musculature might really register as lean on the BMI scale, and nonetheless have an extra physique fats.”

{Many professional} athletes are thought of clinically overweight based mostly on the BMI scale, as a result of it can’t distinguish the load of muscle from the load of fats.

Dr. Lindo Bacon, a physiologist based mostly in California, says individuals thought of “regular weight” based mostly on their BMI can even undergo from ailments like diabetes and coronary heart illness, that are usually related to extra weight.

“I feel that this has been one of the vital damaging instruments in medication in the present day as a result of what we all know is that it is a very poor predictor of well being and that, for instance, there are numerous individuals which can be within the obese and overweight classes that reside lengthy disease-free lives,” Bacon advised CBS Experiences. “However but, they’re put into these classes and advised that they are unhealthy and advised to do plenty of damaging issues that then get in the best way of their well being.”

A bunch of Canadian medical doctors printed new pointers this month urging physicians to rethink the best way they take care of sufferers with weight problems. Amongst different issues, they instructed that BMI shouldn’t be used alone as a instrument to guage well being. “Though BMI is broadly used to evaluate and classify weight problems (adiposity),” they write, “it’s not an correct instrument for figuring out adiposity-related problems.”

Some researchers are advocating for a brand new sort of classification system based mostly on the idea of Adiposity-Based mostly Persistent Illness (ABCD) — focusing extra on the well being points related to weight problems somewhat than physique dimension alone. It will incorporate BMI as simply considered one of a number of issues to assist decide a extra particular and individualized plan of action for sufferers.

Different researchers cite research through the years that point out it’s in truth a helpful predictor of well being outcomes, particularly for these with very low or excessive BMIs. Harvard’s TH Chan College of Public Well being acknowledges that whereas “BMI will not be an ideal measure,” and tends to overstate ranges of fats in people who find themselves muscular or athletic, “most individuals usually are not athletes, and for most individuals, BMI is an excellent gauge of their stage of physique fats.” Monitoring BMI over an individual’s life can present essential perception into whether or not the particular person is at a wholesome weight.

Regardless of its shortcomings, Katz says BMI nonetheless has some worth when taking a look at weight problems tendencies extra broadly.

“The BMI is a crude however great tool,” he defined. “This is why the BMI is a helpful epidemiologic ally: as a result of we don’t have an epidemic of muscularity in america … we do have an epidemic of weight problems. So once you have a look at populations and also you have a look at tendencies in BMI, does it inform you what’s occurring to the weight problems epidemic? Completely. On the inhabitants stage, the extremely muscular group is a rounding error.”

However on a person stage, Bacon argues categorizing individuals based mostly on their BMI does them a disservice, and that we should not depend on it.

“We actually want a way more refined, nuanced dialogue that is going to assist individuals to be more healthy, and it is actually fairly damaging after we make assumptions based mostly on BMI,” mentioned Bacon. “There are plenty of different methods to assist to determine whether or not or not persons are wholesome that give us rather more priceless data than BMI ever can about well being.”

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