Written by Garett Reid | NSCA, CSCS, CISSN, M.S.E.S.S
Fact checked by Kirsten Yovino, CPT Brookbush Institute
FACT CHECKED
When it comes to tracking body composition, there are a variety of ways to do so. For example, you could do it the old-fashioned way and just look in the mirror. However, if you want a more detailed assessment, you’re going to have to use some numbers. With that in mind, two of the more common ways to measure body composition are body mass index (BMI) and body fat percentage. However, what one should you use? Good thing for you, we have the answer.
This article will cover all there is to know about the BMI vs body fat percentage rivalry and answer all of your questions like:
- What is BMI?
- What is body fat percentage?
- Pros and cons of BMI
- Pros and cons of body fat percentage
- Should athletes use BMI or body fat percentage?
- Body mass index or body fat percentage: Which one is best?
How good is your body comp? Let’s find out?
BMI VS Body Fat Percentage
BMI and body fat percentage are two of the more common ways to measure a person’s body composition. On the most basic level, they’re supposed to give you a general idea of how healthy you are by providing an estimate of your weight or muscle composition. However, neither of them gives you the full picture.
While many people talk about these as they’re 100% solid in their information, neither method is perfect as there are plenty of areas to mess up. At the same time, some of their faults come from using them incorrectly. To give you an example, it would be like someone using a hammer to screw in a screw and coming to the conclusion that hammers suck. That being said, BMI and body fat percentage can be useful when they are used correctly. Further, as a lifter, there is a clear winner in what one you should be using.
Before we get to the winner, let’s take a deeper look at the two methods.
What Is BMI?
BMI stands for Body Mass Index and is simply a number that is calculated by comparing a person’s weight to their height. Specifically, the BMI equation looks like this:
BMI= Body Mass/ Height(squared) →Kg/m²
Using this equation will yield a number that will classify your weight and BMI values:
- Underweight: >16-18.4
- Normal BMI: 18.5-24.9
- Overweight BMI: 25-29.9
- Obese High BMI: 30.0->40
Still, some will even make smaller categories but you get the idea. Regardless, Body Mass Index has been completely misrepresented over the years and used incorrectly by almost everybody (that escalated quickly). Let us explain.
It’s often assumed that BMI was invented by the NHS or CDC, or one of the other alphabet organizations as an easy way to instantly assess a person’s health.
Actually, only the latter half of this is true. Concerning the former, the basic idea of BMI was invented over 200 years ago by an astrologist named Adolphe Quetelet. However, he specifically noted that it was not to be used for individuals but rather populations as he had an interest in what he called “social physics”. He felt that the ideal size would be seen most in a community so BMI was his tool to find that.
In reality, BMI is (was) very similar to the Grecian ideal in which numbers were used to distinguish the ideal body one should aim to achieve.
In the 1970’s BMI was reborn by the work of a guy named Ancel Keys. After seeing the dramatic rise of obesity in Western societies, he led a large study to find a fast and easy way to determine some’s relative body composition to determine if they were at a higher risk of disease. In other words, he fully intended BMI to be used for mass measurements to get an estimate rather than be used on a personal basis.
Nevertheless, because it is so simple and our medical professionals are so lazy, it has been adopted as “the” method to determine if someone is healthy (we’ll discuss this more below).
What Is Body Fat Percentage?
Body fat percentage is exactly what it sounds like. It’s a method to measure the percentage of body fat you have on your body. For example, if you weight 200 pounds and you had 40lbs of fat, you would have 20% body fat (40/200 X 100 = 20%). The remaining weight would be made up of fat free mass - muscle, bones, blood, organs, etc.
That being said, it can’t give you the full impression of someone’s overall size. For example, a guy who weighs 150lbs with 30lbs of fat (skinny fat) will have the same body fat percent (20%bf) as a 300lb guy with 60lbs of fat. However, these two will look drastically different.
Regardless, it’s still a much more applicable method to use to answer most people's real question; how fat are they? When choosing what method to use, there are numerous ways to measure your body fat percentage, yet only two are reasonable for the general population.
Skin Calipers:
Using skin calipers is the cheapest and most accurate method for average lifters to check their body fat percentage. However, it requires a skilled individual to make correct measurements. It requires a person to use calipers to measure the amount of fat in various areas of the body. In order to get an accurate reading, multiple measurements will need to be taken from different spots. This is because different people store fat differently, so taking various measurements will correct this as it will give a better picture.
For example, some people store more fat on their thighs so if only that measurement was taken, that person would have a high body fat percentage. However, since they store more fat on their thighs, they won’t have much on their waist or tricep. Therefore, all of these measurements are also taken and calculated together.
Bioelectrical Impedance Analysis:
Bioelectrical impedance analysis (BIA) is one of the more common ways (perhaps most common) that the average population uses to test their body fat percentage. This is due to its simplicity and low cost making it an easy sell from an industry perspective. If you have ever seen any of the home scales that measure your body fat percentage, they are most likely using BIA. Still, you can see other similar devices, such as held devices. Regardless, they work the same way.
BIA works by sending a small electrical current through a person’s body by way of two conductors. As the current travels from one conductor, it must pass through various tissues, mainly fat and muscle. Because these various tissues have different conducting properties, the charge that ends up at the second conductor will give a representation of the body’s composition.
Because people assume electronics are always right, these products are used extensively. While they can give a general idea, they are far from giving an accurate picture. For example, different equations need to be used for different ethnicities and sexes due to the difference in make-up1. Plus, this requires the manufacturer to use the appropriate equation to begin with as there are multiple choices.
Further, a real-life experiment was held by Consumer Reports where 6 individuals used 6 different BIA scales and compared the results to what’s known as a Bod Pod2. A Bod Pod is a piece of laboratory equipment shaped like a giant egg used to measure body comp. After an individual gets in, the BOD POD then measures the difference in air pressure that occurs once the door is closed. This method is highly accurate, which is why it was chosen to give a base measurement. After running through the six different scales, the closest BIA scale was off by 21% of the Bod Pod measurement! The worst? 34%! Still, one even had issues providing a correct body weight! In other words, electronic scales ARE NOT as reliable as we think they are, let alone body fatness BIA scales.
The bottom line is that while BIA seems like a good tool to have in your house, you will need to do quite a bit of research before purchasing one. Basically, don’t buy whatever one is on sale or you’ll likely get a very false reading that can effect your weight loss journey.
Every Other Method:
Other than calipers and BIA, every other method requires laboratory equipment and just isn’t reasonable for the average population to use on a consistent basis. Therefore, for the purpose of this paper, we’re not going to go over them in depth. That being said, these include:
- Bod Pod: We went over this above briefly, but it uses changes in air pressure to measure body composition
- Hydrostatic Underwater Weighing (Water Tanks): Uses water displacement
- Dexa Scan: Utilizes two X-Ray beams.
As mentioned, these are far more accurate and far more expensive.
Body Fat Percentage and Body Mass Index (BMI): Pros And Cons
Now that you have a better understanding of both let’s compare some different variables of body mass index and body fat percentage.
1) Cost:
When it comes to cost, BMI is definitely cheaper as you don’t need to buy anything. Even though you could maybe argue calipers for body fat percentage measurements are cheap, you’d likely still need to pay a qualified individual to take measurements. Further, BIA can range in price, but it doesn’t include “free” like using BMI.
2) Time Requirements:
BIA and BMI are going to take relatively the same amount of time, assuming you have a calculator on hand, no more than a few minutes. However, calipers can take some time to do, AND you need to consider you can’t do it by yourself. Therefore, you’re limited on when you can do it, OR you would need to make a special trip.
3) Effective Use:
This is the one that really counts. As mentioned above, BMI has been misused in the past and continues to be misused by the actual medical profession. BMI is only supposed to give a medical professional a quick glimpse at someone’s health according to their body composition.
However, your BMI is not to be used alone with no other evaluation. In that sense, it’s really not effective as no decisions should be made about one’s health simply by looking at their BMI. Unless it’s being used as a general method to get an approximation of health as a form of triage, there’s really no purpose for BMI.
For example, if doctors or any health professionals hear of two people with a Body Mass Index of 22 and 40, they can guess that the person with a score of 40 is more likely to need more analysis.
In comparison, body fat percentages give a much more accurate picture of someone’s body composition and their risk of disease. For example, 12% body fat is 12% body fat. Still, this can be misleading in extreme cases (anorexia, an individual who uses a substantial amount of PEDs).
BMI or Body Fat Percentage: Who Should Use Them?
So now let's see who should use BMI and who should use body fat percent.
Body Mass Index (BMI):
BMI is a good tool for the sedentary population to get a general idea of how healthy their weight is. That being said, this population should still consider other factors, such as waist circumference. The problem with BMI is that it does not take the amount of muscle into account.
What can happen is that a man who works out routinely can easily be classified as obese due to the extra weight of their muscle. Therefore, taking other variables into consideration can help provide a fuller picture.
For example, there’s a big difference between having a BMI of 36 (obese) and a waist size of 40 and a BMI of 36 and a waist size of 34. The man with a 34 waist size is likely just a huge bodybuilder.
Remember, muscle weighs as much as fat, it's just muscle is a lot denser.
There is also something called normal weight obesity, which is someone who has a normal healthy BMI but they have high body fat mass. This is why BMI is only part of the picture. It's important to measure body fat.
Body Fat Percentage:
Anyone can use body fat percentage, but it should be the primary method of body composition for any athlete or anyone who works out. As mentioned, this population has a much larger amount of muscle which can cause them to artificially be labeled obese by BMI. That being said, this group is much more likely to already know their estimated body comp due to their lifestyle. Still, they probably aren’t so worried about their body comp from a health perspective but rather a performance or aesthetic. Regardless, body fat percentage is definitely the way to go if you are an athlete.
The only group of people where this may not give the total picture are extra-large athletes such as elite Strongmen. In this case, they have such a large amount of muscle it can artificially show a low body fat percent. The percentage is correct, but because they have abnormal amounts of muscle, the coil is carrying around an excessive amount of fat. That being said, this is likely only done with the help of PEDs.
This brings us to the next group where body fat can’t paint the whole picture; elite bodybuilders. Many of these athletes also have an insane amount of muscle on them which can be very stressful on the organs even with a low body fat percent. To be clear, we love these lean mass monsters but even they are aware their lifestyle is risky. Further, we want to be fair and point out that body fat percent is not flawless.
In fact, there’s another group where body fat isn’t appropriate and that would be those with eating disorders. They can have a “healthy” body fat percent but be dangerously underweight. Again, you can never just take one variable alone. However, taking the body fat percentage and then merely looking at a person can drastically improve your analysis.
What's The Ideal Body Fat Percent for Men?
So what should you aim for as far as body fat percent? Some of that will depend on objective reasons, but there is definitely a range that you should aim for.
- General Fitness/Health: For guys who aren’t trying to be on the cover of a fitness magazine or do a show, you should aim for 15-18%. This number is relatively easy to achieve without too much stress about dieting. We’re not saying you shouldn't diet; we’re just saying that you can still enjoy some beer and pizza once in a while and stay in this range easily. Plus, most guys will be happy with how they look.
- Advanced Fitness: If you’re trying to really get in good shape, you should aim for 11-14%. Keep in mind that it gets exponentially difficult to drop a percent the lower you get, as you basically just have essential fat at this point. That means these levels are going to require a little more focus.
- Elite Fitness: This level will include <10% body fat. In reality, this level should only really be sought after by bodybuilders or fitness models. You won’t gain any extra health benefits, and most people aren’t going to be able to tell the difference between 9%-11%. Hell, we probably couldn’t.
In our opinion, we think 12-15% is really the ideal body fat percentage for guys. It’s relatively easy to hit and maintain and looks awesome, assuming they person has muscle. Keep in mind that a guy with a lot of muscle mass will look better at 14%bf than an undeveloped guy at 10%. So again, body fat percentage only tells part of the story, as having muscle mass can greatly enhance your aesthetics at a given body fat percentage.
What's the Ideal Body Fat Percentage for Women?
Women naturally have more body fat than men, so their healthy fat mass numbers will look a bit different, as will assessing body composition.
- Healthy Weight: 21-31%
- General Fitness: 21-25% for those who regularly workout and take it seriously
- Very Athletic: 14-20%
Anything above 32% is technically considered obese for women.
BODY MASS INDEX AND BODY FAT PERCENTAGE: Final Analysis
You should definitely use body fat percentage if you’re wanting to get an accurate picture to where you stand. That being said, understand that there’s also nothing inherently wrong with BMI; it’s just how it has been used. Again, you can’t take your bicycle to a motorcycle race and conclude bikes suck. The BMI does have a role to play, but it’s definitely not for personal health and definitely not athletes.
Regardless, body fat percent will give you a solid answer at your body comp even if it’s off by a few percent. Still, we would still urge you to use other variables in addition. Here are some other methods you can use alongside body fat percent to get a better picture:
- Look in the mirror: Do you like what you see? If you’re at a reasonable body fat percent (18%) but you like the way you look, there’s probably no real reason you need to lose weight. However, be honest with yourself if you have too much body fat.
- Waist size: Men should generally wear a waist size of <36. Even guys weighing 240+lbs who are fit wear a 36 waist size or less.
- Energy/Performance Levels/Mood: All of these can indicate how you handling your training level and diet. If you feel great at 15%bf but then drop to 12%bf and feel like crap, you may need to accept that 12% may be too low for you.
And at the end of the day, be proud of where you are but never content! Always strive for a little bit better every day!
References:
- Dehghan M, Merchant AT. Is bioelectrical impedance accurate for use in large epidemiological studies? Nutrition Journal. 2008;7(1). doi:10.1186/1475-2891-7-26
- Byrne S. Body-Fat Scale Review. Consumer Reports. https://www.consumerreports.org/body-fat-scales/body-fat-scale-review/
Garett Reid
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