Round bellies, jiggling thighs, world-class athletes. Sounds out of place?

You may have seen the seventh edition of ESPN The Magazine‘s Body Issue. If you haven’t, check it out. It is a unique issue that spotlights a variety of athletes’ bodies without their uniforms. Each athlete, at the top of their games, in their birthday suits. The issue shows how different sports favor dramatically different body types.

Besides the cool action shots and unusual locations, we see athletes come in all shapes and sizes. Would you really think of a woman who does 6 hours of training a day as ‘overweight’ because of her shape? It got me thinking: How do you measure health? Ultimately, do size and shape define health?

Let’s start with the first question. There are a variety of metrics that assess health. Skinfold thickness, waist circumference divided by height, underwater weighing, and dual energy X-ray absorption are just a few. But one measurement is used more commonly than all of these: body mass index (BMI).

The concept behind BMI was derived by a Belgian statistician Adolphe Quetelet almost 200 years ago. He wanted an index to study human growth in a population. Quetelet noticed that “weight increases as the square of the height” increased. The practical measurement of BMI was born. (Simply put, BMI is the measurement of your weight in kilograms divided by your height squared—kg/m² or lbs./in.²)

Like anything, BMI has its pros and cons.

One the one hand, BMI is simple, inexpensive, and noninvasive strategy to indirectly measure body fat. It’s indirect because BMI measures excess weight more so than it measures excess body fat. Also, BMI is not able to parse out the difference between excess fat, lean body mass, or fat distribution. Despite this, BMI has been an invaluable tool to track weight in populations over time. It’s also been valuable to screen individuals to identify potential weight concerns.

But is this number of value for individuals like you and me? Maybe not so much. Let’s go back to the Body Issue. ESPN featured Amanda Bingson, USA Track and Field hammer thrower. A BMI calculator tells us her height and weight equate to a BMI of 34.9, nearly 5 points above the marker for obesity. Same with soccer superstar Abby Wambach, whose BMI hovers around 25, right at the cutoff considered ‘overweight.’ Would a healthcare professional qualify these women as obese or overweight? Probably not.

In the article, Bingson sums it up nicely:

“I’m just dense. My arm is just my arm—it’s not cut, it’s not sculpted. I don’t have traps bulging out to my ears; I have a neck. I don’t have a six-pack. My legs are a little toned, but they aren’t bulging out. I’m just dense. I think it’s important to show that athletes come in all shapes and sizes.”

The limitations of BMI extend beyond professional athletes. My best friend is a strong and compact ex-swimmer who has a BMI above 25. This number classifies her as ‘overweight,’ a label that doesn’t fit her. With a few examples, it is clear that health cannot be defined by a single measurement. We’d be better off not giving so much value to a single number like BMI. Instead, it is important to put BMI’s value into perspective. Health can come in a variety of sizes and shapes. It is so much more than a number. 

Photos via ESPN Magazine