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When you go to the doctor’s office, chances are you’ll have to submit to height and weight measurements, which are then calculated to determine your BMI. BMI is the acronym for Body Mass Index, and it’s the current standard for determining if your weight is appropriate for your health. A BMI is a measurement of how much body fat you have.
Your BMI score helps your physician decide if your weight is impacting your health and if further testing is needed. But BMI is not the only thing a wise doctor will consider. “BMI can be used as a screening tool but is not diagnostic of the body fatness or health of an individual. To determine if a high BMI is a health risk, a health-care provider would need to perform further assessments. These assessments might include skinfold thickness measurements, evaluations of diet, physical activity, family history, and other appropriate health screenings,” explains the Centers for Disease Control and Prevention (CDC).
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You can calculate your own BMI by using this formula:
Weight in pounds ÷ (Height in inches x Height in inches) x 703
As an example, if you weigh 180 pounds and are 5 feet 4 inches (64 inches) tall, you’d multiply 64 by 64 (4,096), divide 180 by 4096 (0.0439), multiply that by 703, and end up with a BMI of 30.89.
BMI results are classified as:
- 18.5 or lower: Underweight
- 18.5 to 24.9: Normal weight
- 25.0 to 29.9: Overweight
- 30.0 and above: Obese
Or, you can do it the easy way and just plug in your height and weight into any one of hundreds of BMI calculators online.
Your health-care provider is required to do a BMI, so give him a break when the nurse asks you to step on that scale. The Healthcare Effectiveness Data and Information Set (HEDIS) are health standards required by most insurers to be in your medical records, and one of them is BMI. The insurance companies audit your medical records to be certain these standards are met, using the statistics to measure your physician’s performance in terms of care and service.
Is BMI All It’s Cracked Up to Be?
No one will argue that obesity—and just being overweight—is bad for your health. Studies upon studies have linked excess weight, aka fat, to cardiac disease, diabetes, cancer, and more. A study published in November 2017 The Lancet Diabetes & Endocrinology Journal stated that the combination of diabetes and high BMI (a BMI over 25) were the cause of 5.6 percent of new cancer cases worldwide in 2012, equivalent to 792,600 cases.
However, experts agree that using the BMI system alone to judge determine if a person is obese is unrealistic, because it doesn’t consider anything but weight and height. An article in Medical News Today used this example to illustrate the flaw in the BMI system: Wrestler Steve Austin, at the height of his career weighed 252 lbs. He was 6’ 2” tall. His BMI at 32.4 would classify him as obese. It’s a great illustration of the problem. While a pound of fat weighs the same as a pound of muscle, a pound of muscle takes up a lot more room on your body than a pound of fat.
Although being told at your doctor’s appointment that your BMI is 30 and you’re officially obese might give you pause—and put you on a diet—relying solely on the BMI to make that call may well be antiquated.
The BMI formula was developed in the 1830s by Lambert Adolphe Jacques Quetelet, a Belgian mathematician, well before the plethora of sophisticated diagnostic tools we have today. (Ancel Keys, an American physiologist, dubbed it “body mass index” in 1972.) That original equation has not changed much fundamentally.
In 2013, researchers from the Perelman School of Medicine at the University of Pennsylvania said in Science magazine that a BMI score does not account for critical factors that contribute to health or mortality, such as fat distribution, proportion of muscle to fat, and the sex and racial differences in body composition.
“There is an urgent need for accurate, practical and affordable tools to measure fat and skeletal muscle, and biomarkers that can better predict the risks of diseases and mortality,” says Dr. Ahima exford Ahima, MD, PhD, Professor of Medicine and Director of the Obesity Unit in the Institute for Diabetes, Obesity, and Metabolism. Dr. Ahima believes determining the optimal weight for an individual must take in to account “factors such as age, sex, genetics, fitness, pre-existing diseases, as well novel blood markers and metabolic parameters altered by obesity.”
Better Indicators Than BMI
Body shape appears to be an important factor in whether a person’s weight is impacting health or not. Studies have found that body shape makes a difference—that old pear vs. apple shape—may be more important than BMI.
An Intermountain Medical Center Heart Institute/Johns Hopkins study shows that abdominal obesity, more so than total body weight or BMI, is a strong predictor of left ventricle (heart) dysfunction. “We specifically found that waist circumference appears to be a stronger predictor for left ventricle dysfunction than total body weight or body mass index,” says Boaz D. Rosen, MD, of Johns Hopkins, the study’s principal investigator.
A study from Loughborough University’s School of Sport, Health and Exercise Sciences, published in the Annals of Internal Medicine, found people with a normal BMI who carry much of their weight around their middle are at the highest risk of death from any cause compared to those who are overweight or obese but carry their weight elsewhere. “It is yet further evidence that even if you are within a ‘healthy’ BMI range, but you carry weight around your stomach, your health is still at risk. The message here is that if you do have central obesity, no matter what your BMI, you should take steps to reduce this fat,” says Loughborough Professor Mark Hamer.
A study led by UCLA psychologists found that using BMI to gauge health incorrectly labels more than 54 million Americans as unhealthy, even though they are not. The researchers’ findings are published in the International Journal of Obesity.
“Many people see obesity as a death sentence,” said A. Janet Tomiyama, UCLA assistant professor of psychology and the study’s lead author. “But the data show there are tens of millions of people who are overweight and obese and are perfectly healthy.” The scientists analyzed the link between BMI and several health markers, including blood pressure and glucose, cholesterol and triglyceride levels, using data from the most recent National Health and Nutrition Examination Survey.
They found that close to half of Americans who are considered overweight by virtue of their BMI (47.4 percent, or 34.4 million people) are healthy, as are 19.8 million who are considered obese.
Jeffrey Hunger, a co-author of the paper, says research shows that BMI is a deeply flawed measure of health. “This should be the final nail in the coffin for BMI,” he said. Hunger recommends that people focus on eating a healthy diet and exercising regularly, rather than obsessing about their weight, and strongly opposes stigmatizing people who are overweight.