They're both around the same height, weight, and consequently, they have the same Body Mass Index — or BMI.

But if you split them open Damien Hirst style

or just compare the results of their body scans you can see a slight difference.

Phil has more body fat than Coleman, and Coleman has more muscle than Phil.

Although BMI is a popular measure to assess if a person's weight might be putting them at risk for obesity-related diseases, its results can be pretty misleading and less nuanced than we'd like.

So the BMI is an index that looks at somebody's body weight divided by their height.

So the formula is the body weight in kilograms divided by the height in square meters.

18.5 and below is underweight, 18.5 to 24.9 is your healthy range, 25 to 29.9 is overweight, and a BMI over 30 is classified as obese.

With the idea being that the taller somebody is, the more they should weigh.

Kinda weird how a single decimal point can separate being overweight from being obese.

The major problem with using BMI as a marker of health when it comes to body weight, because it penalizes you if you have a lot of muscle and you're healthier.

Let"s use professional athlete Marshawn Lyncwh as an example.

He's 5'11, 215 lbs, and his BMI is 30.

He'd be categorized as obese.

That is because BMI doesn't distinguish muscle from fat.

We are really concentrating on how much muscle does somebody have, because muscle it's the metabolic engine.

It's the thing that burns calories and the more muscle you have

the easier it is for you to stay at a lower and

more healthy body fat percentage not necessarily a BMI.

In this way, BMI's reliability as an indicator of health breaks down for athletes like Lynch.

There are several more variables that can influence the interpretation of BMI.

Things like age, gender, and ethnicity.

While BMI is a useful measure for a large population study, for example,

to compare relative obesity rates from state to state;

it becomes more problematic when you use it to determine an individual's health.

The body mass index was introduced in the early 19th century.

This guy who created the formula — I'm so sorry, I'm gonna butcher his name,

Lambert Adolphe Jacques Quetelet — wasn't even a physician.

Quetelet was a Belgian mathematician.

And his reason for creating the formula was to study the “normal man”, not obesity.

Its use shifted to study obesity because of Ancel Keys.

In 1972, Keys used the formula in his "Indices of Relative Weight and Obesity” study, renamed

the formula to body mass index, and from there the “new” measure caught on among researchers.

Over the years, its use in the health professional field grew and it's pretty much stuck around since.

It's easy to use, cheap, fast, and its right about 80% of the time.

So even though BMI has stuck around for more than 200 years,

it's not the be-all and end-all indicator.

There are more effective ways to assess to body composition, and overall health.

Hydrostatic weighing, or underwater weighing, is an option.

Along with MRI scans, and waist-to-hip ratio.

Medical tests like checking blood pressure, your glucose levels, resting metabolic rate,

can further give a picture of overall health.

I went to George Washington University, and lab director Todd Miller showed me another way,

using dual-energy x-ray absorptiometry or DEXA image.

It measures total body composition, including fat mass, lean body mass, and bone density.

So the green is the areas where the body is very lean.

The yellow areas of moderate fat.

And the red areas of high fat.

So this person was here July 3rd she had 72 pounds of fat and 109 pounds of muscle.

And in December 27th of this year she had at thirty seven pounds of fat in 115 pounds of muscle.

Using this chart you can see if this person stepped on a scale, they'd only see they lost 29 pounds.

What the scale wouldn't say is that they gained six pounds of muscles,

and BMI wouldn't say that either.

So even if two people have similar BMIs,

that one number will never truly give either of them

the full picture of their overall wellbeing.

BMI is an indirect measurement of one aspect of an individual's health.

So while it can be helpful, it shouldn't be the only way to understand the human body.