You’ve probably had your body mass index—or BMI—measured at one or more check ups since you were a child. Care providers and even fitness coaches use BMI to gauge whether you’re at a healthy weight.
BMI is based on the ratio of your weight to your height and has long been considered a more useful measure of potential disease risk than simply going by the number on a scale. (For background, the standard BMI ranges for adults are: below 18.5=underweight; 18.5–24.9=healthy weight; 25.0–29.9=overweight; 30 and above=obese.)
The thing is, a 19th century mathemetician originally developed BMI as a screening tool to measure population health—not as a tool to gauge individual health. When it comes to personal health, BMI has its limitations. For example, your body composition (your ratio of lean and fat mass) could change, but if your weight stays the same, so will your BMI–making it a bad way to gauge your risk for certain diseases.
Here are other ways BMI is limited and some better ways to track your health and weight.
Why does this matter? Because carrying more weight around your middle—specifically visceral or belly fat—is a much more important predictor of obesity-related diseases such as type 2 diabetes, heart disease, and certain cancers, as well as overall mortality than total body fat levels. And BMI alone cannot determine that risk.
Crazy fact: The original calculations for BMI were developed nearly 200 years ago by a Flemish statistician. They were then updated in the early 1970s using data from only white European men. As a result, its ranges don’t apply fairly to other ethnic groups and people of color.
For example, research has shown that BMI isn’t a good measurement of health among people of Asian heritage because this group may have an increased risk for metabolic diseases before their height and weight calculation qualifies them as overweight.
That’s why organizations like the American Heart Association recommend that doctors use a different BMI scale for Asians that has lower healthy weight cutoff points. Studies have also shown that BMI is flawed in assessing disease risk among people in the Black community. It turns out that higher BMIs are not as unhealthy for Black people as previously thought.
Women tend to have higher amounts of total body fat than men with equivalent BMIs. Guys also have more muscle, on average, than females. Yet, BMI calculations hold men and women to the same weight range standards. It’s also not a great gauge for pregnant and nursing women, who carry more weight and body fat to help nourish their babies. This has been shown not to pose any long-term health risks, despite their higher BMIs.
One of the most famous examples of how BMI doesn’t work for athletes is Arnold Schwarzenegger. When the former California governor was in the prime of his bodybuilding career, he was 6’0” and weighed around 235 pounds—most of which was muscle, of course. His stats gave him a BMI of 31, putting him in the obese range.
What’s more: A study of NFL players found that 60 percent of them would technically be considered overweight or obese according to the BMI chart. That doesn't seem quite right with all that training and weight lifting, does it?
And that’s exactly the problem: BMI can’t measure overall body composition—meaning how much body fat you have versus lean muscle mass. Muscle is more dense and heavy than body fat, so it’s possible to fall into the “unhealthy” range even though that’s likely not the case.
Ever heard the term “skinny fat”? It describes those who are technically at a normal weight— or maybe even underweight—but have a high percentage of body fat that could pose a health risk. And BMI overlooks this.
How does this impact older people? Because as you age, your body naturally loses muscle mass. (Well, without regular exercise, like strength training, to help you maintain it, that is.) This could give you a higher ratio of body fat to muscle—the official term is sarcopenic obesity, or ”skinny fat.” It can definitely occur in younger people, too, but it’s most common among elderly adults.
There is already a lot of guilt and shame wrapped around the topic of weight. And when someone who is overweight or with obesity goes to the doctor, BMI tends to be the focal point of discussion. As a result, other health concerns could get pushed aside. Or that shame may keep people from seeking the preventative care they need, period. This can lead to higher rates of chronic conditions down the road.
It’s pretty clear that BMI is not a one size fits all approach in determining overweight and obesity. While the CDC notes that it’s an inexpensive, simple, and non-invasive way to measure body fat, health is more complex than a simple calculation. And providers who use BMI as the sole determinant for disease may miss the mark.
There are more accurate ways to assess how much body fat you have—and your health. One of the easiest methods is to measure your waist circumference or the distance around your middle right at belly button level. This can help tell you how much visceral fat (belly fat) you have. Excess amounts are tied to health risks, including heart disease and type 2 diabetes. For men, waist circumference should be less than 40 inches; among women, the ideal is less than 35 inches.
Another way to check your health is body composition or percent body fat, which looks at how much of your body is lean mass and how much is fat. According to the American Council on Exercise, women are considered to have obesity at 32 percent body fat, and 25 percent for men.
There are several ways to check yours. For the most accurate measurement with detailed insights, you can get a DEXA scan (dual-energy X-ray absorptiometry), which costs between $150 and $400. Bathroom scales that use bioelectrical impedance are less accurate, but are accessible and can help you track change over time. The least expensive way to measure body fat is a skinfold test done with a pair of $10 to $15 skinfold calipers.
But remember that your size is only one part of the picture! So be sure to factor in these other important measures of health:
resting heart rate
blood sugar and insulin resistance
eating patterns and behaviors
Get the proper tests and talk to your provider about any areas that could use improvement.
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