The Body Mass Index (BMI) is a simple tool to assess whether a person is within a normal weight range for their height. To determine your BMI, take your weight in kilograms and divide it by the square of your height in meters. Those with a BMI of 25 to 29.9 are considered overweight, while those over 30 fall into the obese category.
However, simple does not have to mean simple best. There has been intense research into the use of BMI as an indicator of health in recent years, with many undermining its usefulness and suggesting that overemphasis on BMI may do more harm than good.
This now also includes the American Medical Association (AMA). Here’s what you need to know about BMI.
What is going on?
On June 14, the AMA announced its recommendation for physicians to no longer use BMI solely as a way to assess wellness.
The decision to move away from relying on the controversial height-to-weight ratio stems in part from the fact that the original data collected was based only on previous generations of non-Hispanic white populations.
In the statement, the AMA said it “recognizes that relative differences in body shape and composition between racial/ethnic groups, sexes, genders and age groups are essential to consider when applying BMI as a measure of adipose tissue and that BMI should not be underestimated. used as the sole criterion for denying appropriate insurance compensation.”
Instead, the AMA suggests that BMI should be used in conjunction with other tools to measure obesity, such as “measures of visceral fat, body fat index, body composition, relative fat mass, waist circumference, and genetic/metabolic factors.”
Why there is discussion
On an individual level, BMI has several disadvantages. But it can be a good tool for tracking rising or falling obesity rates in a population.
One reason people love BMI is its simplicity. However, it is the simplicity of this formula that also makes it problematic when assessing individuals. BMI does not take into account muscle versus fat. For example, an athlete may have a low body fat percentage but a high BMI, due to muscle.
When it comes to health, it can also be more important Where you’re carrying fat, something BMI can’t tell you. For example, belly fat has been linked to high blood pressure, type 2 diabetes and heart disease.
It is also possible to have a higher than average BMI and be generally healthy, a condition called metabolically benign obesity. This may be due, at least in part, to the way different bodies respond to fat. Different racial and ethnic groups can also carry and hold different weights.
There is also an important economic reason why BMI should not be the benchmark for weight and health. Insurers may not cover the costs of treatments for people who do not fall into the correct category under BMI. In May 2021, for example the Washington Post reported that a black woman suffering from an eating disorder was told her BMI was too high for her insurance to cover treatment. She had to pay $800 a month out of pocket.
The tool may also underestimate the number of people with obesity. A new study presented at the Endocrine Society’s annual meeting suggests that BMI skips cases of obesity when obesity is determined by fat versus muscle percentage.
Perspectives
There may already be a better measure than BMI
A study published on September 20 analyzed 387,000 adult participants from the United Kingdom and found that waist-to-hip ratio (WHR) – the waist circumference measurement divided by the hip circumference measurement, according to the National Institutes of Health – “has the strongest and most consistent association with mortality, regardless of the BMI.” The study authors suggested that clinical recommendations should “consider focusing on the distribution of adipose tissue compared to mass.”
Waist-to-hip ratio can assess where dangerous fat is better than BMI
Dr. Fatima Cody Stanford, an obesity medicine physician, told VeryWell Health that WHR is probably the better indicator of health. “If we carry adipose tissue (body fat) in our abdomen, it increases our risk for cardiometabolic diseases such as heart disease and type 2 diabetes,” she explained.
BMI is an imperfect tool, but one of the few screening options we have
“Right now, the best tool we have, which is available in every clinic, is screening based on BMI. We need better things,” Dr. Carolynn Francavilla Brown, an obesity medicine physician, told STAT News.[The AMA policy] is a push in the right direction, but we also have to accept the reality of what we have now.”
Focus on BMI can damage the relationship between doctors and patients
“Physicians’ focus on BMI can lead to unproductive conversations about weight, which break the doctor-patient relationship and cause distrust. This can lead to patients choosing not to follow a doctor’s advice, even if that advice is not weight-related, and not pursuing follow-up care due to shaky trust, an essential part of an effective doctor-patient relationship. In addition, misguided BMI assessments can unnecessarily shift the clinician’s attention to weight, a convenient default but often misleading explanation for various signs and symptoms, and can result in missed diagnoses, sometimes with serious consequences.” – S. Bryn Austin, professor of social and behavioral sciences at Harvard TH Chan School of Public Health, and Dr. Tracy K. Richmond, assistant professor of pediatrics at Harvard Medical School, MedPage Today
BMI may be more accurate than we assume in finding excess body fat
“Despite its limitations and infamous counterexamples, BMI is strongly related to body fat and rightly categorizes people as having excess body fat more than 80 percent of the time. Additional simple measurements such as waist circumference can be even more informative, as they provide information about where fat is distributed in the body.” — Kevin D. Hall, senior investigator at the National Institute of Diabetes and Digestive and Kidney Diseases, Washingtonpost
The relative fat mass index (RFM) may be a better measurement, without the need for a scale
“The team of researchers behind RFM say it is more accurate than BMI, and can also be calculated with just a tape measure – so you don’t need a scale to calculate it, as you do with BMI. from RFM it is the distance around your waist in relation to your height that counts, and not your weight. The researchers say this “provides a better idea of whether a person’s body fat is at a healthy level or not.” in California. ‘Our results confirmed the value of our new formula on a large number of topics. Relative fat mass is a better measure of body fatness than many indices currently used in medicine and science, including BMI.’” — ScienceAlert
Weight is still something you should discuss with your healthcare provider, even if BMI is not used
“What I don’t want as a result of this is for people of color and black people in particular to ignore BMI and discuss excess body weight with a healthcare provider because they misunderstand the intent here. The goal is to personalize how BMI is used in medical decision-making and move away from blanket generalizations that can lead to stigma and bias.” –Dr. Jamy Ard, professor of epidemiology and prevention at Wake Forest University School of Medicine, CNN
