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It is a simple little tool that has been used by doctors for decades, but the system for measuring Body Mass Index, or BMI, is coming under increasing fire. Critics have labeled BMI as not only unreliable but sexist and racist, and even many clinicians who value it also acknowledge its shortcomings.
BMI is a formula that uses the height and weight ratio of a person to assess if they are underweight, normal weight, overweight or obese, although it is not a direct measure of body fat. First invented nearly 200 years ago by Belgian mathematician, astronomer and statistician Adolphe Quetelet, it was originally known as the Quetelet Index until the American physiologist Ancel Keys coined the term Body Mass Index in 1972.
According to the Centers for Disease Control and Prevention, BMI is a “cheap and easy screening method” that is “strongly correlated” with weight-related medical conditions – serious health problems, among others. heart disease, stroke, type 2 diabetes, sleep apnea and breathing problems, and various types cancers. About 40% of U.S. adults be seen as obese.
But in recent years, doctors, scientists and dietitians have expressed concern about the deficits of BMI. Although it is used to diagnose obesity – defined as a BMI of 30 or higher – it does not provide information on how weight affects an individual’s health.
“The problem with BMI, even though it adjusts for height, does not adjust for what constitutes weight,” said Dr. David Katz, an expert in preventive medicine and founding director of the Yale-Griffin Prevention Research Center. “That someone who is extremely muscular can have a high BMI and still have a very low percentage of body fat, that’s what you really care about. Someone who has very little muscle could actually register as lean on the BMI scale. , and still have excessive body fat. “
Many professional athletes are considered clinically obese based on the BMI scale because the weight of muscle can not be distinguished from the weight of fat.
Dr. Lindo Bacon, a California-based physiologist, says that people considered “normal weight” based on their BMI can also suffer from diseases such as diabetes and heart disease, which are typically associated with being overweight.
“I think this has been one of the most damaging tools in medicine today, because what we do know is that it is a very bad predictor of health and that, for example, there are a lot of people in the categories with overweight and obese who live long disease-free lives, “Bacon told CBSN Originals. “But still, they are placed in these categories and told that they are unusual and told to do a lot of harmful things that then get in the way of their health.”
A group of Canadian doctors this month published new guidelines that encourage doctors to rethink the way they care for obese patients. Among other things, they suggested that BMI should not only be used as a tool to evaluate health. “Although BMI is widely used to assess and classify obesity (obesity),” they write, “it is not an accurate tool for identifying obesity-related complications.”
Some researchers advocate a new type of classification system based on the concept of Adiposity-Based Chronic Disease (ABCD) – and focus more on the health problems associated with obesity rather than on body size alone. It would include BMI as just one of several considerations to help determine a more specific and individualized course of action for patients.
Other researchers’ studies over the years indicate that it is in fact a useful predictor of health outcomes, especially for those with very low to high BMIs. Harvard’s TH Chan School of Public Health recognizes that although “BMI is not a perfect measure,” and tends to exceed fat levels in people who are muscular or athletic, “most people are not athletes, and for most people’s BMI is a very good measure of their body fat level. “Tracking BMI over a person’s life can provide important insight into whether the person has a healthy weight.
Despite his shortcomings, Katz says BMI still has some value as they look more at obesity trends.
“BMI is a raw but useful tool,” he explained. “Here’s the reason BMI is a useful epidemiological ally: because we do not have an epidemic of muscle tension in the United States … we have an epidemic of obesity. So if you look at populations and you look at trends in “BMI, does it tell you what’s going on with the obesity epidemic? Absolutely. At the population level, the whole muscle group is a round mistake.”
But on an individual level, Bacon argues that categorizing people based on their BMI does them a favor, and that we should not trust it exclusively.
“We really need a much more sophisticated, nuanced discussion that will help people to be healthier, and it’s really very harmful when we make assumptions based on BMI,” Bacon said. “There are many other ways to help find out if people are healthy or not, which give us much more valuable information than BMI can ever about health.”
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