You Shouldn’t Trust Your BMI Score – here’s why

• 8 min read 4


When it comes to measuring an individual’s health, BMI is the most widely used metric in this world. Yet, it is highly overrated. See how it fails to predict your actual health.

BMI is insanely popular. It is very likely that you might have calculated your BMI at least once and been emotional about it (BMI > 25, silently cries in the corner).

As it’s pretty easy to calculate one’s BMI, either using the original formula or using one of the millions of calculators available online, it’s generally accepted as the go-to method to track one’s health.

But, consider this:

According to the standard BMI formula, Steve Cook, an IFBB Pro bodybuilder scores 29.2 on the scale. A score above 25 is considered to be overweight and indicates that the individual might be having health issues or is falling for one. [1]

Does this mean Steve is unhealthy?

Of course not. He is perfectly healthy. His BMI score is just fucked up (sorry, Steve).

Shockingly, this isn’t a single case. Most people who are muscular will have an incorrect reading. Furthermore, scoring low or optimal on the BMI scale doesn’t guarantee you to be as healthy as a horse.

In a study of over 40,000 individuals, conducted by the University of California, researchers found that nearly 50% and 29% of the people who were classified as overweight and obese respectively according to their BMI score, were actually metabolically healthy. [2]

They showed no signs of heart disease, high blood pressure or diabetes.

Interestingly, in the same study, about 30% of the group who had an ideal BMI showed signs of unhealthiness.

Crazy, isn’t it?

But before we get to root cause of this anomaly, let us have a look at what BMI really is.

What is BMI?

According to Wikipedia,

“The BMI is an attempt to quantify the amount of tissue mass (muscle, fat, and bone) in an individual, and then categorize that person as underweight, normal weight, overweight, or obese based on that value.”

Originally named as the Quetelet index, it was developed by a Belgian mathematician named Adolphe Quetelet during the 19th century to gauge the overall health of a country’s population. [3]

Due to its simplicity and ease of calculation, it has since been the de facto standard to determine the health of countless individuals.

Our mantra has been the following, for years:

Need a quick overview of your health? Calculate your BMI.

The BMI formula is actually quite simple:

BMI = Weight (kg) / Height2 (m)

You don’t even need to calculate it manually. A simple Google search for “bmi” will show you something like this:

BMI Calculator Google
Google’s very own BMI calculator.

What does the score say about you?

  • less than 18.5 means you’re underweight.
  • 18.5 to 25 means your weight is optimal.
  • 25 to 30 means you’re overweight.
  • above 30 means you’re obese.

Wow! Is it really that simple to determine one’s health?

Not really. Our body is much complicated than that.

Funny enough, the formula was never meant to determine the quality of health of an individual, and yet it has been used and promoted for hundreds of years by doctors and health specialists.

How is it messed up?

A general misconception is that BMI values reflect how fat an individual is – greater the number, fatter you are.

In reality, however, the BMI formula just factors in your body weight and height and pops out a shiny number like a lottery ticket.

How do you separate the amount of fat in the subject’s body? Fat doesn’t make up for 100% of our body weight.

Our body weight is the sum of weights of everything’s that present in our body – fat, muscle, bones, and water too. Failing to isolate fat composition in our body, BMI fails spectacularly in determining one’s fat levels, contrary to what’s stated in the general definition of the metric.

Another thing to keep in mind is that muscle is about 18% denser than fat. [4]

This means that while you might be muscular and lean, you can weigh more than or same as your friend who’s fat and bulky.

Added bonus, when you plug your weight into the golden BMI formula, it will be happy to classify you as overweight. The fallacy at its best.

Also, being overweight doesn’t mean you’re unhealthy.

Some people might weigh 90 kgs but can complete a triathlon like a boss (I’m gearing up to compete one day).

On a similar note, being classified as optimal on the BMI scale doesn’t guarantee that you’re healthy af. You might weigh less but if most of that weight is made up of dangerous fat, you’re very unhealthy.

Fun fact, BMI will never consider that and you will walk away knowing you’re totally fine – deceived.

Same BMI but different bodies

Same BMI Different People
Illustration Credit: Body Labs

To light up the shortcomings of BMI, Body Labs, a 3D human body modeling startup created the above illustrations based on the data collected by scanning 6 real people.

Although the subjects look very different, they were all 5 feet 9 inches tall and weighed 78 kgs.

Their BMI? 25.4. However, while some of them are really fat, others are quite in shape.

How is this even possible? The same explanation. Some of them were muscular whereas some of them were just fat.

Also, having the same BMI doesn’t guarantee two individuals are similar healthwise. One might be super healthy while the other might be hitting the hospital bed anytime soon.

This illustration is a perfect example of how misleading BMI can be.

Now, you might ask:

Why hasn’t there been any improvement in the formula for years, Rahul?

Actually, there is already a new formula in town (looks like someone else got frustrated with the old formula too).

The new BMI formula

Not isolating fat is not the only problem with the original formula. In the recent past, there has been a lot of controversy on the fact that if you’re too tall or too short, BMI will go even crazier on you.

The human body is complex. We don’t grow in a linear fashion like a cylinder or a cube.

Squaring off our height, BMI sidesteps this fact and results in producing a value that classifies millions of short people thinner than they actually are and tall people fatter than they actually are.

Shocking, isn’t it?

Nevertheless, professor Nick Trefethen at the University of Oxford identified this mistake in the year 2013. In an attempt to correct the mathematical error, he came up with a revised formula, which became popular as the new BMI formula [5].

Here’s the revised one:

BMI = 1.3 * Weight (kg) / Height2.5 (m)

How does it make a difference?

Well, using this formula, every 6 feet tall individual would lose a point from their standard BMI reading while a 5 feet tall will gain a point. Problem solved.

You can try the new formula using this revised calculator to find out where you stand.

Now the question that comes:

Does this solve the original problem? Sadly, no.

It still neither considers your fat percentage nor does it consider your waist size where most of the bad fat is located.

A simple weight by height ration isn’t enough to judge one’s health.

Speaking of bad fat, let’s have a look at what you should be really paying attention to.

What you really need to check

Remember the overpriced good for nothing stuff that you bought last year?

Well, BMI is kind of like that.

Therefore, it’s wise not to put much faith in that golden but faulty number. To get a clear picture of what’s happening in your body, you need to check what’s right above your belt.

Fat Guy Sleeping
Graphic Credit: monsterjoke

Visceral fat or active fat is a dangerous type of fat that is found in our abdominal region. These fat are often found surrounding major organs such as the liver, pancreas and the kidneys.

Being present even below the subcutaneous fat (a layer of fat under your skin), visceral fat is also known as deep fat and is known to cause various diseases like:

  • Heart disease
  • Breast cancer
  • Alzheimer’s disease

Harvard University says that 10% of our body fat is visceral fat. [6]

Since BMI doesn’t factor in the type of fat in our body, a person who scores pretty well on a BMI scale might actually have a lot of visceral fat stored in their body. Not cool.

That doesn’t mean you should be fat-free like every other product in the market. Every one of us has a certain amount of fat in our body. We need fat to live a healthy life.

It is when bad fat like visceral fat starts accumulating at an unprecedented rate, the real problem occurs.

How to measure your body fat?

Unlike jumping on a weighing scale and getting a score, fat takes a little more effort to calculate.

Traditionally, there are many ways to measure your body fat percentage like getting an MRI scan done. However, these tests are often expensive and time-consuming.

Good for you, there are easy and inexpensive ways to get it done. Here are two such methods:

Now, that will still give you the overall fat levels of your body. Wondering how do you find out whether you have too much of visceral fat?

These two measurements will give you a clear indication that things are utterly wrong. You might have a considerable amount of visceral fat if your [7]:

  • Waist circumference: > 35 inches (Women), > 40 inches (Men)
  • Waist-to-hip ratio: > 0.85 (Women), > 0.9 (Men)

It’s worthy to note that these handy methods are just approximations. If these methods indicate abnormal fat levels in your body, you should get a more accurate test done to find out your actual fat levels.

What to do now?

Now that you know that BMI doesn’t give you the clear picture of your health, you should:

  • Use your BMI reading only as a crude indicator of your current health.
  • Measure your body fat percentage using one of the methods above (or both for a better result).
  • Check if you have a lot of visceral fat stored in your body using the methods above.
  • Start eating healthy (healthy foods are not boring, here are 400+ recipes that you can use).
  • Introduce at least one activity (running, swimming, weight training, etc.) in your daily routine.
  • Focus on your overall body composition like body fat percentage, fat-free mass, joint health, etc. instead of relying on a stupid number.

On a side note, just remember, no matter how much body fat you have right now, it can be brought to a healthy level using proper diet and training.

Don’t let some absurd metric trick you. Always get a clear picture of your health.

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READ NEXT: How Your Sedentary Lifestyle is Killing You

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