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If you’ve ever stepped on a scale at the doctor’s office, you’ve probably had your Body Mass Index (BMI) calculated. What exactly is this number telling you, and is it really the best way to understand your health?
What BMI Measures
“BMI — body mass index — is a ratio of your height to your weight,” explains Dr. Stewart Decker, Clinical Wellness Officer & Medical Director at Sky Lakes Wellness Center. “It is that simple.”
BMI is calculated by dividing weight by height squared (BMI = pounds/inches² x 703), categorizing adults as underweight (<18.5), normal (18.5-24.9), overweight (25-29.9), or obese (≥30). So, if you are 5’6” tall and weigh 140 pounds, you have a normal BMI of 22.6.
The simplicity of BMI is both its strength and its weakness. It’s easy to calculate and doesn’t require any invasive procedures. But, while BMI can be useful for tracking weight patterns across large groups of people, when it comes to individual health, BMI falls short in some important ways.
Where BMI Gets It Wrong
BMI has three major limitations:
- First, “for people who are shorter, so 5’2” and under, it will oftentimes overestimate your BMI,” says Decker. The opposite happens for tall people over 6 feet, where BMI often underestimates weight concerns.
- BMI also isn’t accurate for bodybuilders and muscular people. “Arnold Schwarzenegger’s BMI during his bodybuilding prime was in the obese range,” Decker notes. BMI can’t tell the difference between muscle and fat, which means an athletic person might get labeled as overweight (because muscle weighs more than fat).
- There’s also a demographic problem. The formula was created using only Caucasian men in Europe, making it less accurate for women and people of different ethnic backgrounds.
A Better Way to Measure Health Risk
So what should you focus on instead? Your waist circumference, especially when compared to your height.
“Fat deposits or fatty stores that are around your middle are much more important for [assessing] your long-term health than fatty deposits or fat that is stored in your arms or your legs,” explains Dr. Decker. This belly fat, called visceral fat, sits around your organs and creates higher risks for heart disease, stroke, and diabetes.
Research shows that waist circumference provides a more accurate picture of disease risk than BMI alone. Decker says that for women, a waist circumference above 35 inches signals increased health risks; for men, it’s 40 inches.
The waist-to-height ratio is even better. You want your waist measurement to be less than half your height. So, if you are 5’4” tall (64” total), your waist should measure 32 inches or fewer. “I love to use the waist to height ratio,” says Decker. “That’s a much better evaluator of an individual’s health.”
What Really Matters for Your Health
Your weight might matter less than you think. “Your behaviors, such as how much sleep you get, how much exercise you get, how much and what types of foods you’re eating, and how much stress you’re dealing with” have bigger impacts on your long-term health, according to Decker.
Instead of obsessing over your BMI, focus on eating vegetables, staying active, getting enough sleep, and managing stress. These habits protect you from heart disease, stroke, diabetes, and other chronic conditions better than reaching a specific number on the scale.
