You eat your greens and do a solid mix of cardio and strength-training all week long—so why the heck is your body mass index (BMI) so high? Well, if recent research is any indicator, you shouldn’t necessarily be stressing over that number quite so much. It turns out that BMI may not be much more than, well, a number.
If you’ve been to a primary care physician—ever—you’ve probably had your BMI calculated. It’s pretty simple: Your body mass index is your weight divided by your height squared in meters. The resulting number is supposed to reflect whether your weight is in a healthy range.
According to the World Health Organization, a normal or ‘healthy’ BMI would fall between 18.5-24.99, an overweight BMI would be between 25-29.99, and an obese BMI would be anything 30 and above.
Here’s the issue, though: The formula for BMI doesn’t take muscle mass, bone mass, or the physical differences between men and women into consideration, says Michelle May, M.D., founder of AmIHungry.com.
BMI was first developed by a mathematician in the nineteenth century to assess the health of population groups—not individuals, says Stephen Box, a certified fitness trainer and nutrition coach in Suwanee, Georgia. “If you look at it statistically across big groups of people, you would notice that it’s fairly accurate in determining the overall level of obesity,” he says. “But the problem is when you try to put it to an individual.”
Since BMI doesn’t take anything other than weight into account, explains Box, it doesn’t provide a full picture of your health. For example, someone who has 12 percent body fat and tons of muscle could have the same BMI as someone with 40 percent body fat—but the more body fat you have, the higher your risk of developing things like diabetes, high blood pressure, high cholesterol, and even certain types of cancer. Not to mention, genetics plays a part in your health and risk levels for disease, explains May, which is certainly not something BMI can take into account.
Because of these limitations, you could theoretically be fit and healthy, but be classified as obese according to your BMI. “A bodybuilder may have a high BMI because of all the muscle mass that they have relative to their height, but just simply looking at their BMI could lead you to make an assumption that they’re unhealthy,” says May.
Making assumptions around BMI don’t get us very far. A 2013 study published in JAMA actually found that those in the “overweight” BMI range had a lower risk of death than those in the “normal” range. Plus, a 2016 study published in the International Journal of Obesity found that 34.4 million Americans who are considered overweight (according to their BMI) are actually healthy, according to benchmarks like blood pressure, cholesterol, and insulin resistance. The same goes for the19.8 million who are considered obese by BMI standards.
The bottom line: Since BMI doesn’t indicate anything about your current health or diseases you could be at risk for, there’s really no use in obsessing over it, says May. Instead of looking for ways to lower the number, focus on practicing good habits—like consistently eating whole foods and veggies, and being active for 30 minutes every day. “Your daily lifestyle is a better indicator of whether you’re going to be healthy than just a number,” says Box.