Need a refresher on what Body Mass Index (BMI) is? It’s a weight-to-height ratio, explains Dr. David Creel, Ph.D., RD, a psychologist and registered dietician at the Bariatric & Metabolic Institute at Cleveland Clinic. To calculate BMI, divide your weight in pounds by your height in inches squared, and then multiply it by the conversion factor of 703, he says. If that sounds a little too complicated, there are several online BMI calculators out there, like this one from the National Heart, Lung, and Blood Institute. Based on the BMI calculation, people are classified into a weight status category, according to the Centers for Disease Control and Prevention:
Underweight: BMI below 18.5Normal or healthy weight: BMI of 18.5 to 24.9Overweight: BMI of 25 of 29.9Obese: BMI of 30 and above
The CDC says BMI “can be a screening tool, but it does not diagnose the body fatness or health of an individual.” And, experts say BMI often unfairly labels people based on their size and appearance. Parade.com asked health professionals to explain how BMI is used today and whether it’s still a necessary tool.
How is BMI used?
What we know as the Body Mass Index was created by a Belgian mathematician, astronomer and statistician Adolphe Quetelet as Quetelet Index in the 1800s. Based on his interest in human physical characteristics, he developed the index to estimate a population’s rates of overweight and obese residents to help governments determine how to distribute health funds. The scale was renamed the Body Mass Index in the early 1970s. Even Quetelet said early on that BMI isn’t the best measure of an individual’s health, but instead offers a general glimpse into a population. Still, BMI is widely used today in health care settings, most often for epidemiological or public health purposes, in clinical environments and by insurance companies, says Dr. Janet Tomiyama, Ph.D., associate professor in the Department of Psychology at the University of California Los Angeles. “It was considered an advancement at the time to just look at someone’s weight by incorporating aspects of their height,” explains Dr. Tomiyama, who also serves as director of the UCLA Dieting, Stress and Health Laboratory. “Now, we know based on the science that it has many flaws.”
Is BMI still a useful measurement?
Dr. Tomiyama calls BMI an “antiquated measure,” explaining that it doesn’t provide the full picture of health or account for indicators like blood pressure and cholesterol. Instead, she says it “focuses only on the number on the scale.” The index is still useful, Dr. Creel says, but more context is needed in the BMI conversation. “I just think we need to make sure we look at it in the context of a lot of other things,” he says. BMI should be used strictly as a screening tool that looks at population averages of how height compares to weight, and the health risks that affect that population. “It’s not great if we just pull one person out of the population and say, ‘Oh, based on your BMI, you’re high risk or not high risk,’” Creel adds.
What role does BMI play in weight stigma?
Putting too much emphasis on BMI as a gauge of health can unfairly and incorrectly label people as unhealthy, says Tomiyama, and that fuels weight stigma, which can lead to discrimination and mental health consequences. In a study published in the International Journal of Obesity in 2016 and led by Tomiyama, researchers analyzed the connection between BMI and health markers like blood pressure and glucose, cholesterol and triglycerides. They found that about half of Americans whose BMI categorizes them as “overweight” and about 30% of those labeled “obese” were actually metabolically healthy. “By looking just at someone’s weight and height, you simply can’t tell what’s going on underneath the skin,” she adds. “All it’s doing is labeling individuals as unhealthy when they might not be, and that comes with all this baggage and societal stigma and also licenses individuals to stigmatize heavier individuals.” Weight stigma is linked to a higher risk for anxiety, depression and eating disorders. Tomiyama says it also increases stress, triggering the brain to release the hormone cortisol, which could actually make people gain weight. How BMI is applied can also be racist and discriminatory, Tomiyama says. Black and Hispanic women have higher rates of obesity and being overweight than white women, according to the U.S. Department of Health and Human Services Office of Minority Health. “Naturally, if who we’re stigmatizing are the people who are heavier, then it’s going to be these racial and ethnic minority populations,” Tomiyama says. “So we really need to pay attention to these intersections of stigmatized identity.”
So, what’s a more accurate, equitable measurement?
People with higher BMIs are at greater risk for developing certain health conditions, like heart disease, high blood pressure, type 2 diabetes and some cancers, according to the National Heart, Lung, and Blood Institute. But a high BMI isn’t always correlated with poor health. BMI should just be a starting point for understanding someone’s true health risks, Dr. Creel says. What someone eats, how much physical activity they get, whether they smoke and how they carry their weight are equally important. “We know that if someone has excess weight, but they’re more physically active, it reduces their risk for disease,” he explains. Someone who smokes, for example, may have a lower BMI, but smoking leads to a host of health issues. And people who carry their weight around their midsection are at greater risk for disease. “I want to know what their body composition is,” Dr. Creel says. “So, are they a BMI of 28 and they’re very muscular, or do they have a BMI of 28 and they have really thin arms, thin legs and a larger abdominal region? Those are all the things we want to look at.” To more directly assess health, it’s also important to consider blood pressure, blood glucose, triglycerides, cholesterol and physical fitness, such as whether someone can climb a flight of stairs without feeling pain or being out of breath, Dr. Tomiyama says. “I think everybody’s goal at the end of the day is health,” she adds. “And, if being healthy is your goal, then Body Mass Index is not healthful information. A way more direct route to health is to actually look at health.” Next, read about the mental health benefits of exercise.
Sources
Dr. David Creel, PhD, RD, a psychologist and registered dietician, Bariatric & Metabolic Institute at Cleveland ClinicDr. Janet Tomiyama, Ph.D., associate professor, Department of Psychology at the University of California Los AngelesCenters for Disease Control and Prevention:About Adult BMICleveland Clinic:Americans Concerned About Their Weight, but Don’t Understand Link to Heart Conditions and Overall HealthInternational Journal of Obesity:Misclassification of cardiometabolic health when using body mass index categories in NHANES 2005-2012National Heart, Lung, and Blood Institute:Calculate Your Body Mass Index National Heart, Lung, and Blood Institute:Assessing Your Weight and Health RiskNephrology Dialysis Transplantation:Adolphe Quetelet (1796-1874)–the average man and indices of obesityStatPearls Publishing:Physiology, Body Mass IndexU.S. Department of Health and Human Services Office of Minority Health:Minority Population Profiles
