The Body Mass Index, or BMI, scale has been around for nearly 200 years at the time of this post. Developed by a mathematician, it is rooted in faulty information and needs to disappear.
This is especially true since we have a slew of scientific data accumulated over the past two centuries that discredits the BMI and its usage.
Unfortunately, there is no absolute measurement system that is going to be 100% accurate with body fat percentage. But at least we have technology that is a bit better than a basic calculation of a height-to-weight ratio.
Where Did the BMI Come From?
The BMI dates back to 1832, initially devised by Adolphe Quetelet. As an avid statistician, mathematician, and astronomer, Adolphe designed the calculation to exhibit the “normal man.” The idea was to create a method of health analysis by quantifying the overall structure of the human body.
It wasn’t until the 1950s when Louis I. Dublin (Metropolitan Life Insurance Company) integrated the Quetelet Index into tables to gauge life insurance policyholders and found that more people on the obese side were filing claims.
In 1972, physiologist Ancel Keys took the Quetelet Index and ran with it, coining the formula as the Body Mass Index while providing evidence from a study conducted of 12 samples from more than 7,000 “healthy” men.
Today, the BMI is widely used in medical records as a way to assess the risk of a variety of diseases known to affect the obese, such as heart disease and diabetes.
How Does the BMI Scale Work?
The BMI is calculated by taking a person’s weight in kilograms and then dividing it by their height, squared. It’s been since converted to pounds, feet, and inches. There is nothing more to it. Just from the calculation alone, you can start to see why it’s a flawed system from the jump.
The formula looks like this:
BMI = weight (kg) / height (m)₂
This BMI score is then compared to a table of weight samples. The numbers include:
- BMI Under 18.5 = Underweight
- BMI 18.5 to 24.9 = Healthy Weight
- BMI 25 to 29.9 = Overweight
- BMI 30 to 39.9 = Obesity
- BMI 40+ = Severe Obesity
How the BMI Is Terribly Flawed
It’s dumbfounding for me to understand why doctors still use the index scale in the 21st century. There are some things that can’t be quantified by numbers, and body fat is one of them. There are several things that will cause the scale to deliver false information, which is a bad thing when physicians and health experts use it to determine plans and therapy.
For example, some of the things the BMI doesn’t take into account include:
Total Muscle Mass
Muscle weighs more than fat. It’s much like how gold weighs more than lead; it’s all about density. Muscle weighs more because the cells are more tightly packed compared to fat. And it’s this density that causes the index to give a false positive for obesity.
This is why someone can weigh over 300 pounds and not look as “fat” as someone else. That first person could simply have more muscle mass than the second.
It’s not that a pound of muscle weighs more than a pound of fat. They both weigh a pound. It’s the fact that a pound of muscle will take up less room on your body than a pound of fat.
Bone Density
The human skeleton makes up roughly 14% of a person’s total weight. And like muscle mass, the density of the bones is reflected on the scale. Those who have a more dense skeletal structure will weigh slightly more than someone who doesn’t.
Bone density can be the result of anything from genetics to increasing in physical activity.
The increase in weight may be within a few pounds, but it’s enough to trigger the scoring on the BMI to put someone into a category of weight that’s not necessarily reflective of his or her health.
Water Retention
Water retention is another aspect that will cause the scale to fluctuate. In fact, your body can increase its weight by five pounds or more depending on how much water you’re retaining. And this would easily cause a false positive on the BMI.
Of course, water retention can be bad for you if not addressed. Nonetheless, you can retain water for a myriad of reasons and weigh more when you step on the scale.
200-Year Evolution?
How much evolution happens within a 200-year window? According to available data, the average height of a man in the 1800s was 5’6″ and weighing roughly 139 pounds. Unfortunately, we don’t have the most accurate health data from that era for obvious reasons.
However, the average height of a man today is about 5’9″ and weighing in at around 190 pounds.
With what we have available, it appears as though the average man has become taller and heavier over the last two centuries. Yet, some of that weight may also include the obesity epidemic and how a vast portion of the populace is considered overweight.
But that, too, might be taken with a grain of salt considering the World Health Organization is using the BMI to determine those numbers. So, a lot of folks who are simply very muscular will trigger the obesity mark on the scale.
The problem is that there is just not enough data to support whether men have grown over the last 200 years, especially since medical records of the 1800s are sparse and not nearly as expansive as they are today.
But if it’s true that men have become larger over the centuries, it stands to reason the BMI would be absolutely obsolete.
5 Examples of Who the BMI Says is Obese
Not everyone who is considered “obese” by the BMI is actually layered in fat like many would assume. In fact, there are a lot of people who tip the scales despite being in prime physical condition.
Let’s take a look at a few celebrities and put their numbers into a BMI scale calculator, shall we? For this little experiment, we’re using the BMI calculator at the National Institute of Health. We’re also using Google results for the celebrities height and weight, which may also be somewhat skewed depending on a plethora of factors.
Still, it’s a good exercise to demonstrate the flaws of the body mass index.
Dwayne “The Rock” Johnson
Dwayne Johnson is one of my favorite comparisons, mostly because of how much of a beast the man is comparatively. The Rock is 6’5″ and weighs in at around 260 pounds. This puts his score at 30.8, which is considered obese on the index.
As you can see, he doesn’t fit the idea of what “obese” looks like. The man is a freakin’ wall of meat. But according to the index, he would have to lose a lot of weight to be “healthy.”
Javonte Williams
Running back for the Denver Broncos, Javonte Williams is another example of muscle mass and definition. Of course, being a running back, he has to be in amazing physical condition to play the game and be capable of smashing his way through some of the largest men on the planet. Anyway, Javonte is 5’10” weighing around 218 pounds.
According to the index, he is more obese than Dwayne Johnson with a score of 31.3. Hell, that puts him relatively close to my score and I’m not even a fraction as fit as Javonte.
Jarred Kelenic
Let’s take a look at someone a bit smaller in stature. Jarred Kelenic, left fielder for the Atlanta Braves isn’t the pinnacle of muscle development, but he’s not a couch potato, either. Standing at 6’1″ and weighing 206 pounds, he scores 27.2 on the index. That puts him shy of obese, but halfway through overweight.
In reality, Jarred is not overweight and is in good physical condition. But according to the BMI, he could stand to lose a few pounds, which is ridiculous all things considered. He would have to weigh 189 pounds to be just under being overweight.
Mike Tyson (the 90s version)
Iron Mike Tyson – one of the most vicious heavyweight boxers in history. The youngest-ever champ weighed between 215 and 220 pounds during his career in the 90s. He stood at 5’10”, making him much shorter than a lot of his opponents. But as Tyson demonstrated, it’s not always the size that makes a winner.
Anyway, according to the BMI, Mike Tyson was obese while in the ring with a score of 30.8. This is taking into account his lightest weight at 215 pounds. And I promise you, he was anything but.
Chris Hemsworth
Most of us know him as Thor from the Marvel Cinematic Universe, but Chris Hemsworth has had quite the career. Regardless of his role, the BMI is doing him dirty as well. Let’s take his size in “Thor: Love and Thunder.” It was the biggest he had ever become for the role, mostly due to COVID lockdown boredom. At 6’3″ and weighing 231 pounds, he scores a 28.9 on the BMI scale.
According to the index, Chris is a little over a single point away from being considered obese. And although his portrayal of Thor in End Game would be more realistic to the index, Chris was in immaculate condition for Thor 4.
What These Examples Prove
No, I didn’t just assemble a list of the who’s-who of sex appeal. But there is a common denominator; all of these men trained hard to become a shining example of athleticism.
What this demonstrates is that when you add any kind of weight training into your workout regimen, the BMI becomes a useless tool that holds no bearing. This is aside from the fact that you could just have a dense skeletal structure or have more muscle than the average Joe.
You don’t need to look like Chris Hemsworth or Dwayne Johnson to tip the scales from muscle mass. Remember, muscle is more dense than fat. That means you could lose sizes in your pants or shirts but still weigh the same after maintaining a workout regimen. It all depends on how much fat you’re losing while adding muscle.
Using Bioimpedance Scales
Perhaps a better tool to use for figuring out your body mass is to use bioimpedance scales. These devices send a slight electrical charge throughout your body and use mathematical equations from cell impedance to determine body fat percentage, bone density, protein mass, and more.
Essentially, a bioimpedance scale measures how fast electrical currents travel through the body while calculating the resistances from bones, fat, muscle, etc. However, they are not viewed as being absolutely accurate. Mostly, that’s because there is a lack of supporting evidence on store-bought devices and the quality of the technology. Yet, they are far more accurate than a simple height-to-weight ratio equation.
Nowadays, bioimpedance scales are relatively cheap and can offer quite a bit in terms of determining your body’s composition. While they may not be the most accurate, they are still quite useful in determining changes in your body after certain diets or exercise programs.
What is a DEXA Scan?
A DEXA scan is a low-dose X-ray scan that is used to measure calcium and such in the bones, the makeup of fat, and muscle composition. It’s quite painless and is often used to test for osteoporosis, which usually affects the elderly.
Obviously, you can’t simply order a DEXA machine for your home considering the radiation danger of using X-rays. But it is quite a bit more accurate for determining body composition over anything resembling the BMI Scale.
In a nutshell, DEXA is primarily for those who need a closer look at the benefits of using the information versus the risks involved with exposure to X-rays. So, it’s not like you can just walk into your nearest Walgreens and ask to be radiated.
Fitness is More Than a Number on a Scale
The point of all of this is to show just how flawed the BMI scale is and why it needs to be retired. It’s an inaccurate calculation that doesn’t take into consideration a lot of things that can cause your weight to fluctuate. There is more involved than just a height-to-weight ratio when it comes to physical fitness.
Instead of worrying about the BMI, perhaps the best method is to try bioimpedance scales. I’ve been using one for several years now and it’s offered a great deal of information. However, I do have to agree about the quality of the technology. Sometimes the cheaper devices are going to give less than accurate results.
Something else I try to focus on instead of the BMI is physical performance. How much can I lift or walk today than I could this time last year? I’m always working on self-improvement.
I try to keep an eye on my development and where I need to focus.
Don’t worry about what the BMI says. It’s 200 years old and means less today than the video game awards.