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Maybe you’ve heard of this initialism before and maybe you’ve even done your own calculation. However, I’ve got another calculation for you: this calculation = dumb (if you do want to know your BMI anyway, you can use this BMI calculator).

First, the history of BMI:

B.M.I. stands for Body Mass Index and it actually was developed in the 1830s by this mathematician named Adolphe Jacques Quetelet. Now Quetelet over here was not a physician, in fact, he was a statistician and was obsessed with identifying averages such as what the average human looked like (what does that mean?...yeah, we’re getting there just hold on). From here, he went on to create BMI which is weight in kilograms divided by height in centimeters squared. Why though? Basically, he had all this data and he made a formula to make the data fit rather than making a formula that could explain data consistently over time (see the problem? I’m sure his statistician friends suffered depression from his regressions...sorry had to say that). Now, BMI sounds like a relatively modern idea, but this was made in the how did it become so popular so recently?

Well, it’s because of a couple of factors, but the first one is because of this other guy named Ancel Keys. In the 1970s, Keys said that BMI was accurate and the way to go to determine health. Keys also gained a lot of popularity because he did studies on saturated fat and health and gained notoriety so when he mentioned BMI, people ate it up (ba dum bum)...especially health and life insurance companies.

For insurers, like Metlife, they now had a very simplistic way of determining someone’s health so that they could charge a proper premium for life and health insurance. If you want to read more about this story, Psychology Today has a great article posted here. However, this doesn’t mean that it’s right. In’s not and here are a couple reasons why:​



#3: The Math makes no sense at all

Why do we divide in math? We divide because we are either trying to figure out the rate of something such as Velocity = Distance/Time or Miles per Hour or we divide to figure out proportions such as $0.10/$1.00= 10%. There is no mathematical justification of why you would divide weight by your height squared. It sounds very scientific and fancy, but what is that getting at? At best, it is telling you how much weight you have per square unit of your body. Sounds scientific, but the root is nonsense.

#2: Sex & Age apparently don’t matter when determining health

(BMI says “All these people in the photo...obese”)

Let’s look at the equation one more time:

There’s nothing about sex, age, bone density, adamantium coated bones or body fat, yet we continue to use BMI. Needless to say, men and women have different body types and “fit” is not the same for both sexes. Additionally, how are you going to say that someone 19 and someone 91 should have the same range of BMI to still be deemed “normal”? Makes no sense! This concept is overly simplistic and as a result it just does not provide any real value when males, women, young athletes and senior citizens are all measured on the same scale to determine obesity.

Obviously as we age over time, our bodies change. We become shorter and our bones become less dense. Because of this, our BMI will change. Even if we did not change physiologically, there is still a huge reason why BMI would still be dumb.

#1: Muscle mass, Bone Density & Body Fat aren’t considered which means 1974 Arnold Schwarzenegger in his prime would be considered Obese

(BMI says “Oh definitely obese. Hey Arnold! Eat a carrot once in a while)

This is the biggest reason why BMI is dumb. Your weight is made up of every cell you have in your body. Additionally, muscle is denser than fat which means that 1 liter of muscle weighs about 2.3 lbs whereas 1 liter of fat weighs 1.98 lbs (more at this Livestrong article). This picture below shows what 5 lbs of fat looks like compared to 5 lbs of muscle.

​Here are the BMI ratings for various celebrities. Some sound accurate, but many just don't.

Understanding your Body Fat % range is a better way to measure your health

So what do you use if you can’t use BMI? A much better way to gauge your health is to use your Body Fat % range. Now, you’re not only looking at a number, but you’re looking at a range that changes with age and sex. For instance, if you’re a 21 year old male, your healthy Body Fat % range would be very different than if you were a 50 year old female. That allows for a range of health that changes with you as you grow and develop.

Additionally, men and women collect fat in different areas of their bodies and Body Fat % range takes that into consideration. Women collect more fat cells in their chest, triceps and butt than men and men collect more fat in their gut than women. Now, there are several ways to collect body fat % and here are the pros and cons of the popular ways:

Not that great- An electronic scale or handheld analyzer:

Not very accurate. These scales measure your Body Fat % by sending a small electrical signal through your body and timing how long it takes to receive the signal back. As electricity moves faster through water and muscle than fat, the longer it takes, the more body fat you must have. However, these scales are often inaccurate because there are several factors that can change their rating such as how much water you drank, having callous feet, dirt on your scale, etc.

Better- Body Fat % calipers:

To use calipers you need another person- don’t do it on yourself because you won’t be relaxing your body and could sway your results. For the calipers, you want to take the average of three measurements per area on your body to make sure your results are as accurate as possible. For women, the areas to measure are at your tricep, hip and thigh. For men, it’s your chest by your armpit, stomach and thigh (if you are interested, I created a tool for you to enter your measurements, age and sex and it will spit out your results and show you how you compare to athletic ranges. Click the button at the bottom to get access.)

Very Good- Water Displacement (aka Dunk tanks):

This is one of the best way to measure your Body Fat %, but it is tough to do consistently.  Because fat is more buoyant in water and muscle is less buoyant, water gets displaced differently. First, your weight is measured on land using a scale. Then you are put into this tank and your weight is measured underwater after you blow all the air out of your lungs. Comparing these two weights determines your true Body Fat %.

Very, Very Good- Air Displacement

Similar to the water displacement, these pods work by measuring how much air your body displaces. The reason why this is a bit better than water is because it is more comfortable and doesn't require a person to be wet. The basis of this tech is a simple formula you may remember from physics if you paid attention: P1V1=P2V2. That is Pressure x Volume should equal Pressure x Volume in the same space is everything is equal. This means that a calibration is taken at the beginning to get P1 and V1. Then you sit in the pod and the has a wall that can move a bit to change pressure. So now P2 is determined and locked in. Now they can figure out your V2!

From here, another equation is used: Density= Mass/Volume. So your density is determined along with some other constants.

Note: You will need to breathe through a breathing tube so that you don't disrupt air flow and thus volume.

Best- X-Rays! aka DEXA (Dual-Energy X-Ray Absorptionmetry- DEXA)

Last one. So this one is very accurate in that it can very precisely measure density as it uses X-rays go through fat, bone, muscle and anything else you may be hiding in your body to determine your composition. One of the negatives is that you are exposed to X-rays, but the machines are fairly safe and limit exposure. 


So what do I use to determine my Body Fat % Range?

If you have access to the Dunk Tank go try it out. If you don’t then buy some calipers, get a friend to measure you and send your email to get my tool to help you measure and record your Body Fat % so you can see where your health is and track it over weeks and months. For many of us, we want to get healthy, but just don’t know what to do. The first step is understanding where you and this is the smart way to do it over BMI. Be smart. Don’t Be My Idiot (that’s the only initialism I could think of). Now go get healthy!

P.S. If you're in Chicago, a good source to help you determine body fat %/density is Dr. Smith at My Optimal Health Chiro.

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