Why BMI's a Bad Indicator of Health

We're made up of fat, muscle, organs, bones and more. The distribution of all those things matters.

Body Mass Index's reputation is irrevocably tarnished, going back a few years when doctors dissected its shortcomings, to earlier this year, when a study from the University of California-Los Angeles found that 54 million Americans whom BMI classifies as overweight or obese are not (said the study author to the Los Angeles Times, "This should be a final nail in the coffin for BMI."). Here's what is replacing it, according to Mark Hyman, M.D., medical director at Cleveland Clinic's Center for Functional Medicine. And here are the other numbers that matter most. 

The problem with the BMI is that it doesn’t tell the whole story; it doesn’t take into account where the weight is distributed. If more is around your waist than your hips, then you are more at risk of disease and are more obese.

There are people out there that simply don’t fit the “typical” body type. Take Shaquille O’Neil for example. This guy was a professional basketball player at the height of his profession and he scores a 30 on the BMI. By BMI standards that would put him in the obese category. But would you call Shaq obese? 

People with large amounts of muscle—like professional athletes—may have a high BMI but not have too much fat. That’s because their weight is distributed in a way that makes sense for their bodies.

There are a few ways to figure out your body composition. The most accurate way to assess this information is by using special tools.   

The best method available in hospitals and special clinics is a DEXA body composition. It uses the same technology that measures bone density and gives the most accurate representation of your body fat because it measures all compartments separately—legs, arms, and belly. If your legs and arms are thin but your belly is fat, you are still in trouble. For men, the ideal composition is 10 to 20 percent of their total body weight as fat. For women, it is 20 to 30 percent.

You can also use special scales which measure total body fat percentage, but don't identify if the fat is more in your legs or your stomach, which has different implications for your health and weight loss. Calipers represent the least accurate method. 

If you don’t have access to these tools, or you can’t find a doctor that has them, you can use your waist-to-hip ratio to get an idea of your body composition. Your waist-to-hip ratio is exactly that: It is the relative size of your belly to your hips, and it gives a general picture of the location of your body fat.

To figure out your waist-to-hip ratio, measure the circumference of your waist around your belly button in inches. Take this measurement and divide it by the circumference of your hips at their widest point. A normal waist-to-hip ratio for men is less than 0.9. A normal waist-to-hip ratio for women is less than 0.8.

Let’s carry on with the example above. I’m 6’3" and 180 pounds. The circumference of my belly equals 34, and the circumference of my hips equals 44. I take the first measurement and divide it by the second measurement, resulting in a waist to hip ratio of .77, which is in the normal range.