Body mass index (BMI) is a simple calculation of your weight divided by your height, a formula devised in the 1830s by a Belgian mathematician that is still used as a way to categorize people as underweight, normal weight, overweight and obese. But the widespread usage of BMI has come under fire, and for good reason — even the developer, Adolphe Jacques Quetelet, said the formula should be used to determine obesity within a population, not as a way to gauge the health of individuals.
So, what numbers should you actually use to determine your health, and whether you’re on a good track? Certainly not scale weight alone, which can be equally problematic. Instead, consider using one or more of these numbers and start charting your progress this way instead:
If you want a much more relevant and equally simple formula, try this one: Divide your waist circumference by your hip circumference. This is your waist-to-hip ratio (WHR), sometimes known as your waist-to-stature number.
Even if you’re not overweight and are physically active, the WHR can help identify your risk of future cardiovascular problems as well as metabolic issues, because belly fat plays a huge role in both, according to Vitor Engrácia Valenti, PhD, a professor at Sao Paulo State University in Brazil.
“The BMI calculation is based on height and mass, which may lead to failure in providing precise information concerning belly fat measurement,” he noted. “This type of fat is a better risk predictor, and other studies have observed that waist-to-stature ratio can better detect hypertension and metabolic syndrome compared to BMI.”
Using a WHR calculator provides an indication of your risk level for health problems related to higher WHR, such as heart disease, Type 2 diabetes and some forms of cancer.
Everyone needs some body fat — according to the American Council on Exercise, men who aren’t athletes should have 14–24%, and women should have 21–31% — but when your number creeps higher than that, especially if it’s much higher, you may be putting yourself at risk for significant health issues including cardiovascular disease and diabetes.
You don’t need to be overweight to have a body fat percentage issue, either. You might be considered normal weight or even underweight, but if your body fat is high, it can still put you at risk. This is the “skinny fat” phenomenon, also known as normal-weight obesity, and it indicates that you could be holding fat around your organs — known as visceral fat — particularly in your midsection.
Some home scales measure body fat percentage, as well as lean muscle mass and water weight You can also get this measurement from personal trainers at your local gym, who should be trained to use devices like skinfold calipers.
In conjunction with lower body fat mass, it’s important to increase muscle mass, particularly if you’ve had weight fluctuations in the past.
Starting in your 30s, you naturally begin to lose some degree of muscle mass and function — a process called sarcopenia — and sedentary people can lose as much as 3–5% of muscle mass each decade. That can have a serious ripple effect in terms of strength and function, and significantly raise the risk of disability.
Weight cycling can make this change even more dramatic, because of how the body puts that weight back on, according to Dr. Andrea Rossi of the Healthy Aging Center at the University of Verona.
When you regain weight after losing it, you’re adding more fat than you had originally. Rossi says fat mass can prevent amino acids from working efficiently within skeletal muscle, and may also reduce protein synthesis. So, your muscles aren’t getting what they need to maintain or build strength.
“If you’ve had weight cycling, also known as yo-yo weight changes, it’s even more important to focus on increasing your muscle mass,” Rossi says. That may take the form of strength training or resistance training, and emphasizing that over cardio.
In general, it will take a seismic shift in medicine to eradicate BMI completely, especially since it’s such a simple calculation.
But it’s definitely flawed (for example, Dwayne “The Rock” Johnson is considered obese when using only BMI), and it doesn’t give the best snapshot of your health. By focusing on numbers like your WSR and lean muscle mass, you can have a more meaningful measure of your progress.