Hi, I’m Mike. This is me:
I’m 6’2, 190 pounds, and ~8% body fat. And according to a standard body mass index (BMI) calculation, I’m overweight.
If I want to be in the “normal” range, I need to lose 10 pounds…and that would still put me in the fatter end of normal.
Well, as you can see, body mass index (BMI) is useful for analyzing populations but not so great for analyzing individuals. And especially individuals with more muscle than normal.
And this is why you, someone looking to get fitter, shouldn’t pay attention to your BMI but your body composition instead.
And in this article, we’re going to break down what body composition is, how to measure it, and finally how to improve it.
Many people mistake body composition for body fat percentage or BMI but they’re completely different.
BMI is calculated from your height and weight–it’s your weight in kilograms divided by your height in meters squared.
For example, here’s how I calculate mine:
And here’s how BMI values are correlated with body weight status:
Underweight = <18.5
Normal weight = 18.5–24.9
Overweight = 25–29.9
Obesity = BMI of 30 or greater
As you can see, according to the BMI, I’m as good as overweight.
Body composition, on the other hand, is looking at what your body is actually made of.
When you step on a scale, your weight is a reflection of the amount of skeletal muscle, fat, bones, organs, blood, water, and several other more minor components in your body. There are varying amounts of these things from person to person.
Skeletal muscle usually ranges between 30 and 50% of total weight. Fat can be under 10% of body weight (very lean) or as high as 40 to 50% (morbidly obese). The brain weighs a few pounds, bones are generally about 15% of total body weight, skin weighs about 6 pounds, blood is around 7% of body weight, and so forth.
Now, there are several models of determining body composition, but the one most relevant to our needs splits the body into two components:
This simple model of body composition allows you to better analyze what happens to your body when you diet or exercise.
For example, if your weight goes down but fat-free mass remains the same, you’ve lost fat and not muscle. Hooray!
If, however, you make the common mistakes of severely restricting calories, doing too much cardio, and eating too little protein, you’ll lose weight but it will be a combination of fat mass and fat-free mass.
This is how people wind up “skinny fat.” Doh!
Practically speaking, you have to accept some fat gain if you want to maximize muscle growth, but if your fat mass is rising faster than your fat-free mass, you’re eating too much.
And the only way to know this is to keep an eye on your body composition.
Use this workout and flexible dieting program to lose up to 10 pounds of fat and build muscle in just 30 days…without starving yourself or living in the gym.
Now that you know what body composition is, let’s talk about measuring/calculating it.
The easiest way to go about measuring your body composition is to first measure your body fat percentage. This allows you to determine your total fat mass and thus your fat-free mass.
This sounds easy enough but can actually be fairly tricky, mainly because of the inaccuracy of common methods.
Let’s take a look at each.
Body composition scales like this one from Tanita and various handheld devices are popular but also highly unreliable.
These instruments use a method called bioelectrical impedance analysis (BIA) to measure your body fat percentage.
This involves passing a light electrical current through your body and measuring resistance to it. Muscle, which is over 70% water, conducts electricity well whereas fat, which holds much less water, doesn’t.
There are several problems with BIA, though.
The methodology is inherently handicapped.
Electricity will take the path of least resistance through your body. That means it will avoid fat stores for less resistant tissues. (If someone has a large amount of subcutaneous fat, for example, the current will pass through internal tissues instead.)
Furthermore, many two-electrode devices, like popular scales and handhelds, miss entire parts of your body. Foot-to-foot devices miss the entire torso and handhelds miss the lower half. As you can imagine, this further hurts accuracy.
Another methodological problem with BIA is the readings are equation-based predictions, which can be way off.
When a manufacturer develops a BIA device, they measure the body fat percentage of a large group of people using another method like hydrostatic weighing.
They then test the same people with their BIA device, compare the readings, and develop an equation to predict results based on height, weight, gender, and other variables.
The purpose of the equation is to predict what your body fat percentage would be if you were measured using the “gold standard” method to calibrate the device.
This sounds good in theory but what if the benchmark method is wrong?
Well, that’s often the case.
Hyrdrostatic weighing is the most common method used for guideline measurements and research shows it can be off by as much as 6% due to various factors like ethnicity, body weight, and hydration status.
(And as a note, when I refer to error rates throughout the article, I’m talking in absolute, not relative, terms. In this case, that means someone at 10% body fat might register at 16% when measured with hydrostatic weighing.)
As you can imagine, when you calibrate inherently flawed BIA devices on faulty hydrostatic measurements, the whole method becomes more or less useless.
Testing conditions can dramatically influence readings.
If you’re dehydrated when you test, the increased electrical resistance will result in falsely high body fat levels.
Exercising also greatly skews BIA measurements. Research shows that the body’s resistance to electrical current is lower after exercise, which leads to an overestimation of fat-free mass and underestimate of fat mass. In one study, this post-exercise reduction in bioimpedance resulted in a fat-free mass reading that was 25 pounds too high.
It’s for these reasons that the researchers have said that consumer-grade BIA devices aren’t reliable for individual readings but can be useful for tracking changes in body composition over time.
That is, they may not give the right readings but, over time and many readings, will be fairly consistent in their inaccuracy. This, then, gives you an idea of how your body composition is changing.
BIA is just too all over the place to place any faith in it, even if you try to control for factors like hydration, food, and exercise.
Scientists aren’t using scales bought at Target.
The handicaps of BIA apply to high-end BIA devices, and the gadgets sold to consumers are even less accurate. (They tend to underreport body fat levels.)
The bottom line is BIA is far too inaccurate to be useful in measuring body composition.
Skinfold testing involves using calipers to measure the thickness of your skin at various points on your body.
The measurements are added together and plugged into an equation that approximates how much of your body is fat-free mass. Another equation is applied to determine body fat percentage.
As you can already tell, there are quite a few ways this can get screwy.
User error is a major issue here. Grab too little skin/fat and you’ll get a falsely low reading. Grab too aggressively and it’ll be falsely high. The equations used to turn skin thickness readings into a body fat percentage are also subject to error.
These deficiencies aren’t just theoretical, either.
In one study, skinfold testing underreported body fat percentage by an average of 6%. Individual discrepancies were worse, ranging from measurements that were 10% higher than reality to 15% lower.
Despite their drawbacks, calipers can be quite useful in measuring and tracking changes in body composition, which is something we’ll talk more about in a minute.
By its very nature, the look of various body fat percentages varies widely depending on how much muscle someone has.
For instance, a 160-pound guy at 10% body fat has 16 pounds of fat, and a 190-pound guy at 10% has only 3 pounds more fat but 27 pounds more fat-free mass (and a large percentage of this would be lean mass).
As you can imagine, these are dramatically different looks. And here’s a perfect visual of this:
Both of these guys are around 10% body fat but the guy on the left has quite a bit more muscle, giving him a dramatically different look.
That said, you can guesstimate body fat percentage with decent accuracy by just comparing your body to the following images.
As you can see, the “six pack” starts to show around 10% in men and 18% in women.
Ab/core vascularity starts to appear around 8% in men and 15% in women.
And the paper-thin, “grainy” skin look requires 6% body fat or less in men and 13% or less in women (and, I might add, isn’t healthy to maintain for long periods of time).
Taking regular pictures in good lighting won’t help you measure your body composition but is a great, low-tech way of monitoring changes in it.
DEXA involves a full X-ray of your body to measure levels of fat, bone, and all other fat-free mass. Each of these substances absorb x-rays in different ways, which allows them to be isolated and quantified.
Although DEXA may sound like an infallible way to determine your body fat percentage, it’s not.
Many bodybuilders have learned this through personal experimentation. Despite being in contest shape (body fat levels so low that going any lower will land them in the hospital), some guys will DEXA at anywhere from 6 to 8% body fat.
There are several reasons for this.
So those are the problems. How significantly do they affect accuracy, though?
Well, two studies found that individual error rates using DEXA were as high as 4%. That is, you could DEXA scan at 8% but really be 12%. Or you could DEXA scan at 12%, go and reduce your body fat percentage by 4%, and show no change at a re-scan.
As you can see, despite its high reputation among some fitness folk, DEXA just isn’t accurate enough for tracking changes in body composition.
The Bod Pod is a machine that works much like hydrostatic weighing but uses air instead of water.
The machine measures the amount of air your body displaces inside a chamber and uses equations to determine body density and composition.
You already know that hydrostatic weighing can be very inaccurate, but unfortunately for the Bod Pod, it can be even more so. In one study, individual error rates were as high as 15% and other studies showed individual error rates ranging from 5 to 6%.
One of the reasons that the Bod Pod is generally less accurate than hydrostatic weighing is its results are affected by more variables like facial hair, moisture, body temperature, and even the tightness of the clothing worn.
I can personally attest to the rather shocking readings that can come from the Bod Pod.
I’ve worked with quite a few people whose body fat percentages regularly Bod Pod tested 5 to 10% higher than they really were (you don’t need more than your eyeballs to see that a guy around 10% body fat is most definitely not around 20%).
Like everything else discussed so far, the Bod Pod is too inaccurate in measuring body composition to be relied upon.
The only way to measure your body composition with 100% accuracy would be to remove all your fat, muscle, bones, and organs and weigh them. And I doubt you care enough to volunteer for that.
Everything else is a prediction and as you’ve seen, some methods of prediction are better than others but none even come close to absolute accuracy for all people.
If you’ve been paying attention, though, you’re probably wondering what methods scientists were using to determine the relative accuracy and inaccuracy of these methods. That is, what were they comparing BIA, DEXA, Bod Pod, hydrostatic weighing, and skinfold results against to see how well they work?
What’s the “gold standard”?
Well, it’s a method known as a 4-compartment analysis that involves using several techniques to separate the body into four “buckets”:
Hyrostatic weighing is used to measure body density, total body water is measured through deuterium dilution, and total bone mass is determined by DEXA scan. All of this data is then fed into equations that give you a consistently accurate measurement of body composition.
The problem with this method of determining body composition is obvious: you need access to a team of scientists.
What, then, is the best and most convenient way to measure and track body composition?
While a 4-compartment method is the most accurate and thus theoretically the best, it’s not practical unless you have ready access to everything needed.
For the rest of us, I recommend a much simpler solution: use calipers, a scale, a measuring tape, and the mirror.
Weigh yourself daily and calculate an average every 7 to 10 days.
Your weight can fluctuate on a daily basis due to things like water and glycogen storage and bowel movements (or the lack thereof), so watching and fretting over your weight on a daily basis can quickly become a neurosis.
This is why some people weigh themselves infrequently–once every 2 to 4 weeks–which is fine, but if you want to really keep an eye on things, I recommend weekly averages.
Doing it is easy: every day, first thing in the morning, after the bathroom and before eating or drinking anything, note your naked weight down. Then, every 7 to 10 days, add them all up and divide by the number of days and voila, you’re done.
The changes in that average over time will tell you what’s really happening with your weight outside of the temporary fluctuations that having nothing to do with gaining or losing fat or muscle.
Take weekly caliper measurements.
Extrapolating body fat percentage from caliper readings is dubious but the actual readings themselves are very useful.
If your skin is getting thicker over time, you’re gaining fat. If it’s getting thinner, you’re losing fat.
Also, unlike BIA, which is inconsistently inaccurate, with a little practice, skinfold testing can be consistently semi-accurate. That is, the body fat percentages you calculate may be slightly off but they will be consistently off (1 to 2% too low or high, for instance).
Here’s the caliper I use:
One of the things I like about this caliper is it’s a one-site testing method, which means you can do it yourself.
I was skeptical of its accuracy at first, of course, but was surprised to find it just as accurate or more accurate than several multiple-point methods I’ve tried.
Here’s how to use it:
Again, you don’t have to even bother with the body fat percentage calculation but it does seem to be fairly accurate (within 1 to 2% if used correctly).
Take weekly waist measurements.
The size of your waist, when measured at the navel, is a reliable indicator of fatness. If your waist is shrinking over time, you’re losing fat. If it’s growing, you’re gaining.
This is why I recommend you measure it weekly and record your measurements. Nothing fancy is needed here–just a good ol’ measuring tape.
Take weekly pictures.
What you see in the mirror is a reliable indicator of how your body composition is changing.
Take weekly front, back, and side pictures in good front-on lighting and, over time, you’ll clearly see what’s changing (and what’s not). And remember that if you’re getting leaner in the mirror, you’re losing fat, regardless of what the scale might show.
As you can see, determining your exact body fat percentage can be very tricky if not impossible. You’re going to have to settle for a guesstimated range.
That said, you can track changes in your body composition very accurately, which is what matters most.
Now that you understand what body composition is and how to measure it, let’s talk improving it.
You can improve your body composition in two ways:
These two goals summarize everything we’re looking to achieve with our bodies. Whatever look you want, it’s going to require building a certain amount of muscle and having a certain amount of body fat. (Yes, that applies to women as much as men.)
That said, you can only build so much muscle before you reach your genetic potential and body fat levels can only go so low before health is compromised.
Check out this article to learn more about natural muscle growth potentials and in terms of body fat percentages, here are some workable guidelines:
Stage Ready Bodybuilder
3 – 5%
6 – 8%
Natural “Off-Season” Bodybuilder
10 – 12%
18 – 20%
Maintainable With Strict Diet
9 – 12%
16 – 19%
11 – 18%
21 – 28%
The first thing you need to know is you’re not going to get to “stage-ready” levels of body fat naturally without screwing up your body.
If you’re a man, your testosterone is likely to plummet to near-castrate levels. If you’re a woman, you’re probably going to lose your period (which can have serious long-term health consequences).
Your metabolism, immune system, and thyroid and growth hormone levels are going to be suppressed, and your workouts are going to suck, you’re probably going to deal with constant fatigue, and your mood is going to be depressed.
You know those guys and gals you follow on Instagram that stay absolutely shredded year round and prattle on incessantly about their #dedication to “crushing” workouts?
Well, they wouldn’t be able to do it without steroids.
It is possible, however, to stay very lean year round (~8% in men and ~15% in women) if you’re willing to stay strict on your diet.
I can say from personal experience maintaining ~8% for about a year now that, as time goes on, it gets easier and easier. This is likely due to adaptations related to the body’s “set point.”
Too many mainstream diet and fitness “gurus”–and too many people in general–are far too preoccupied with weight. Losing weight, gaining weight, maintaining weight, and so forth.
Here’s the thing though:
Thinking in terms of body composition is much more useful.
You don’t want to just lose or gain weight–you want to lose fat and gain muscle. And weight is only one indicator of how well you’re doing this.