For years, your body mass index (BMI) — a screening tool that uses a complex calculation to measure your body weight in relation to your height — has been used to determine your weight category: underweight, normal weight, overweight or obese. Your weight category helps your doctor plot your weight loss needs and perhaps make recommendations on medications or lifestyle changes to manage your health risks.
However, while BMI may be useful in tracking obesity trends nationally and worldwide, it’s come into question whether it’s a good indicator of an individual’s health and health risks. It does not, for example, accurately measure body fat, which is a useful measure of health.
What is BMI?
BMI is a screening tool that assesses a person’s weight category. There are many online BMI calculators here you plug in your height and weight, and it spits out your BMI. Without access to such a calculator, you can figure yours out by multiplying your weight in pounds by 703. Then, dividing that number by your height in inches, squared.
(Weight x 703)/(Height in inches x height in inches)
Under 18.5 is considered underweight. A BMI between 18.5 and 24.9 is normal. One between 25 to 29.9 is considered overweight, and someone with a BMI of 30 or more is classified as obese. According to the CDC, more than two-thirds of the US population is considered overweight or obese.
While the CDC has used the BMI to track obesity rates and disease risk factors in the general population since only the 1980s, the BMI calculation has, in fact, been around for almost 200 years.
The history of BMI
Originally called Quetelet’s Index, the BMI was developed by a Belgian mathematician named Adolphe Jacque Quetelet in the 1830s. His goal was to determine the characteristics of the “average man.”
His equation, based on French and Scottish participants’ measurements, was eventually co-opted by American researcher Ancel Keys, PhD, who was looking for a reliable means to determine weight classification and obesity’s effects on heart disease.
Keys reviewed other indexes and declared Quetelet’s Index the best of the lot. His research, also based on predominantly white populations, renamed this tool, body mass index. His paper was published in 1972, but it would take a decade before the National Institutes of Health adopted it as their measurement of obesity and about another decade for the NIH and WHO to adjust the categories to the ones we use worldwide today.
Why your BMI is not the be-all to health
While it’s not a bad idea to know your BMI, keep in mind, it is just one piece of the puzzle that makes up your overall health. For example, it does not take into account lifestyle habits such as smoking or other health measurements such as blood pressure or cholesterol level, which are also essential nuggets of information that factor into your long-term health outlook.
BMI is also not always a good measure of a person’s body fat percentage since muscle weighs more than fat. Therefore, a person with a high percentage of lean muscle and a low body fat rate may get categorized as obese. Additionally, your BMI doesn’t take into account where your fat is accumulated. Fat that settles around your abdomen puts you at a higher health risk of developing cardiovascular disease than fat around hips and thighs.
And lastly, studies have shown that BMI is not as useful for some ethnic populations in determining health risks. For example, Asians may see increased health risks before they reach an obese BMI. And African Americans tend to have higher muscle mass and lower body fat than Caucasians, so their health risks may be lower than white people with the same BMI.
BMI is not a one-size-fits-all tool for health risks or weight goals. If your goal is to get and stay healthy, don’t fixate on your BMI, but don’t ignore it out-of-hand-either. While a high BMI does not automatically mean you’re in poor health, it can mean you’re at a higher risk of poor health.
Other health factors to consider
Some experts say the measure of your waist circumference is a more useful measurement of unhealthy body fat since abdomen fat is especially harmful. A waist circumference less than or more than 40 inches for men and 35 inches for women is a good screening for health risks such as heart disease and type 2 diabetes. Other numbers to consider with regards to your overall health and risk for disease include:
- Your age
- Blood pressure
- Blood sugar
- Cholesterol
- Heart rate
- Bone density
Additionally, your family history and lifestyle such as how active or inactive you are and whether you smoke also factor into your overall health and risk of chronic diseases. In fact, smoking, for example, is the most preventable cause of death in the US.
Perhaps, one of the most important indicator of your health is how you feel. Are you winded when you walk up a few flights of stairs? Are you often tired? Do you feel sluggish or depressed? While numbers, such as your BMI, can shed some light on your health, you know if you’re not sleeping or eating well or sitting too much.
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