Why are we still using an almost 200-year-old formula to determine who’s fit or fat?
We’re talking, of course, about the body mass index, or BMI, developed in 1832 by a social scientist to explain variations in humans’ shapes and sizes. Unfortunately, it has a major flaw: It doesn’t account for the fact that both bone and muscle weigh more than fat.
So, according to BMI, the average muscle-bound NFL linebacker would likely be categorized as “obese,” and top sprinters—who have maybe 8% body fat on a bad day—would score as being at least a bit overweight, a 2014 study showed.
But an “off” BMI rating can do more than keep you in the dark about your fitness level—it can also cost you money. Insurance companies still relying on BMI can use a bad score to jack up premiums, says osteopath Scott Costley, D.O., a triathlete and sports medicine specialist in Rhinebeck, NY, who worries that doctors and insurers are using obsolete tools.
Plainly put, BMI is a useless metric that belongs in the dustbin of history. Fortunately, though, there are many newer, more accurate ways to gauge your level of fitness. Here are five of the best.
1. Do the easy math
If your waist circumference is less than half your height, that’s a good sign you’re fit. This waist-to-height ratio, which Costley uses for himself and his patients, is a far better predictor of overall body fat percentage and heart health than BMI, a new study by Leeds Beckett University found.
2. Get a DEXA
A DEXA, or DXA, a type of X-ray used by many pro sports teams to assess athletes’ health, yields exact body composition—fat, muscle, bone—and can also show muscle imbalances. The cost is a downside: $100 to $1,000 per scan, which insurance may or may not cover.
3. Do the hard math
Your body shape, not just your body fat percentage, strongly correlates to overall health. Excess belly fat, measured using a shape index, is a huge predictor of mortality.
But now there’s an even better overall indicator of risk from many diseases: SBSI (for Surface-based Body Shape Index), a volume measure of your shape. The problem: Measuring yourself for SBSI is a bit tricky, so recruit a friend to help, and use one of the many online SBSI calculators to automate calculations.
4. Buy a high-tech scale
Both the ShapeScale ($599) and Naked Scale ($999)—which use infrared to create a 3-D avatar that, via app, shows fat/muscle displacement—are potential game-changers since, unlike a DEXA, you can do it at home.
You can target specific goals, like building your pecs, then compare your past and present avatar shapes. These scans also show imbalances you need to address. Naturally, too, you’ll see exactly where you have to fight fat. These are our favorite smart scales of 2017.
5. Use "Body Volume Indicator"
Body Volume Indicator compares your total body volume with your belly's, essentially measuring your ratio of total body fat to visceral fat. Using an iPad and the BVI Pro app, a doctor, exercise physiologist, or dietician can measure your BVI by entering your vitals (height, weight, age, gender, and level of fitness) and taking two photos of you (one from the front, and one from the side). The app then divides your body into seven 3D "slices" to analyze your body volume and composition.
In less than 30 seconds, the app will measure your volume of body fat, visceral fat, abdomen volume, waist-to-hip ratio, BMI, and your unique new BVI number—a more holistic picture of your overall health and fitness.