Body Fat Tests: Valuable Tool or Total Waste of Time?

Curiosity killed the cat but it made the humans smarter. When you start focusing on getting healthier, more fit, or losing weight eventually you get curious about your body fat percentage. There are a few things to note before even looking into which test conduct, if any at all.

All tests are wrong to a certain degree.

Huh? Why would anyone use a test that is inaccurate? The thing is, what may be inaccurate on an individual level can be very useful on a population level when statistical significance is taken into account. Take BMI for instance. The Body Mass Index (BMI) is often called out as a ridiculous tool because you can be jacked with single digit body fat but according to the BMI you are overweight or worse, obese. That type of classification doesn’t bode well for someone with body dysmorphia, I’m looking at you bodybuilders. When applied to the population as a whole the BMI is a very useful tool for determining the overall health of the country, outliers like bodybuilders are a small percentage that barely effects the overall outcome of calculations.

Think of it like target practice at a shooting range (what could be a more American analogy than combining obesity and guns into one analogy?). From a distance all your shots are generally around the bullseye, it looks pretty good. After taking a walk to your target you realize there is one round that went high and right (probably pulling too hard with your trigger finger….anyway). That one shot is an outlier that is not representative of the overall accuracy of your shooting. Just like at the shooting range those people who are in excellent shape but still fall into the overweight (I’m guilty of this) or obese category (I’m bordering on this) are outliers who are not indicative of the entire population.

Okay now that you understand whichever method of body fat test you choose will be somewhat inaccurate what should you do about it.

Stay consistent with your measurements or chosen test location and administrator. You may not get a perfectly accurate reading on whatever test you choose but if you remain consistent with your measurements over time you will be able to rather accurately show change over time. The same rings true for measuring your weight on a scale, always measure yourself under the same conditions with the same scale in order to maintain consistency of error.

Now let’s take a cursory look at the science behind calculating body composition before we talk about the actual tests that you could have administered.

The Compartment Models

Body composition tests can be broken down into various categories that generally correlate to the level of accuracy. The first and simplest category is the Two-compartment model.

The Two-compartment model breaks the human body into two distinct compartments fat mass (FM) and fat-free mass (FFM). Certain values are assumed for the density of FM and FFM respectively. Typical methods for the Two-compartment model are Hydrodensitometry “underwater weighing” and Air Displacement Plethysmography (ADP). A typical issue with Two-compartment model methods is that there is no room for individual variability in fat-free mass which is quite common from human to human.

The Three-compartment model is the next category and more accurate than the Two-compartment model. The Three-compartment model breaks the body down into three compartments FM, FFM, and Total Body Water (TBW) or bone density. These methods don’t typically take into account differences in types of FFM, for example bone mineral density and actual lean muscle tissue though they are the most accurate single iteration tests you can get. DEXA is a Three-compartment model test.

The final category is the Four-compartment model.  There is no test that can do the entire Four-compartment model on its own. Multiple tests must be conducted that can measure FM, TBW, and FFM broken down into bone mass and the residual components. The only assumption is the value of the residual fat-free mass. As is taught in 4th grade algebra it’s pretty easy to solve for one unknown variable in order to get a body fat percentage.

The Four-compartment test is the Gold Standard. You will see that most companies claim their machines to be the Gold Standard in body composition measurements, DEXA, BIA, and BOD POD are three culprits in this marketing scheme. The only true Gold Standard, however, is the combination of multiple tests that give enough variables to calculate the Four-compartment model.

body fat tests valuable tool or total waste of time

The Tests

Now that you have a general understanding of what is actually being measured in these tests let’s look at the actual individual tests and see which is the most, practical and realistic for you. The tests are broken down into three categories indirect methods (observational, noninvasive methods), direct methods (include some type of physical intervention), or criterion methods (AKA most expensive).

Indirect methods

Known as Anthropometric measurements including Weight, Stature (height), Body Mass Index (BMI). Techniques such as Circumference Measurements and Skinfold Techniques fall into Anthropometry. Both of these measurements take skill but little else. You can learn how to measure your own body circumference measurements here. Skinfold measurement techniques are an art that is slowly dying due to the newer more “accurate” machines mentioned below. Though if you are able to find someone with a steady hand and experience in measuring skinfolds you may be able to get a fairly accurate reading with little hassle or financial burden.

Bioelectric Impedance Analysis (BIA) is another indirect method of measurement. BIA machines send an electrical current through the body, based on resistance they estimate the total body water (TBW), fat-free mass (FFM), and fat mass (FM). BIA tends to be more accurate on a population level than on an individual level, this is true of all methods because of fancy statistical analysis, but especially true of methods that tend to have greater thresholds of error for the individual. BIA machines are calibrated for certain populations that assumptions are made for, because of this if you are not in that population the machine was calibrated for the body composition estimate the machine gives you can be quite wrong indeed. When using a BIA try to find the type that uses both your hands and feet for the electric current, they tend to be more accurate and consistent than the machines that only use your feet.

Direct methods

Total Body Water is a direct method in which a person consumes a certain isotope that can be measured in the body, the isotope dillutes throughout the body over a set period of time into the water contained in the body. It is then measured to get how much total water is contained in the body. Once this is measured it is used to predict the amount of fat-free mass in the body. Simple subtraction then allows for the calculation of fat mass. There are two important assumptions to note in this method; one, that the relationship between total body water and fat-free mass is constant, and two, that the time of measurement after the isotope is fully diluted is correct and not premature or too late.

Two other less known and used direct methods of measuring body composition are Total Body Counting and Neutron Activation. Total body counting measures the amount of naturally radioactive potassium in the body. From the measured potassium levels fat-free mass can then be estimated. This method isn’t really used that often because there are few machines that are capable of doing it, nothing to be said of its accuracy or potential for error. Neutron activation is some crazy Bruce Banner Incredible Hulk shit. A person is exposed to Gamma radiation which somehow affects the constitution of cell nuclei. Needless to say this method isn’t widely used because of the high levels of radiation that are blasted into, through, and around subjects going through the procedure.

body fat tests valuable tool or total waste of time

Criterion methods

These methods are considered more accurate and reliable than the direct and indirect methods.

Body density: Both Hydrodensitometry (underwater weighing) and Air Displacement Plethysmography (ADP) estimate body composition by measuring body weight, volume, and residual lung volume. These methods both have their own associated issues. For instance underwater weighing is difficult for certain patients because it is hard to fully submerge them underwater, you know like old people, children, and the physically incapable. ADP makes certain assumptions about tissue density which can yield inaccurate results if the assumptions are off. Issues aside both of these methods are a fairly accurate method for measuring your body composition, just ensure that you continue to go to the same machine for follow on assessments to ensure consistency.

Dual-Energy Xray Absorptiometry (DEXA) is fast, relatively harmless, and easy to use. The DEXA machines blast two low-energy level waves through the subject which have the ability to discriminate between adipose tissue, soft tissue, bone mineral content, and bone mineral density. Some studies have shown that DEXA has a tendency to overestimate fat-free mass, this means you may think you are more muscular than you actually are. If you have an overly honest friend or relative they should help keep your head from getting too big from this slight over estimation. All DEXA machines vary, just because one machine reads one body fat percentage another might read something different. All machine models and manufacturers make differing assumptions in their equations that they input into the machines at programming, there is no coherence across machines. So again, frequent the same establishment for your follow on tests.

Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) are also known to be used to get body composition readings. Both machines are in high demand for other tests and procedures for this reason they aren’t generally used for body composition. In addition technicians need to train on how to conduct body composition procedures and upgrade their machine’s software. If you are able to find a place to conduct one of these tests for you consider yourself lucky…. Also keep into account that because these methods aren’t widely used there is potential error in their measurements that is not fully realized.

body fat tests valuable tool or total waste of time

The Gold Standard

The four compartment model is the gold standard for measuring body composition. The idea that there is a singular Gold Standard  is a misnomer. There is no one technique or machine that measures in the four compartment model. Multiple tests are needed in order to calculate the four compartment equation. Typically this is conducted by combining DEXA for bone mineral mass, Underwater weighing or BOD POD for body density and body fat, and Total Body Water dilution to measure total body water.

If the Gold Standard is really required for scientific analysis then multiple tests must be conducted and then combined to get the most accurate possible reading. This makes sense actually when you put it in simple terms. As an individual it would be nice to get a Gold Standard reading but it is often outside of reasonable expectations. Many funded broad scope scientific experiments can’t even get Gold Standard testing for their research. If you can find a place to do it expect to pay a premium.

Is It Even Necessary?

Ultimately body fat percentage is a number you don’t need. You can live a perfectly happy and healthy life and never get your body composition measured. Shit, you can lead a perfectly happy, healthy, and successful figure competitor or lingerie model career and never get your body composition measured. What truly matters for health is how you function, how you perform, and how you look at the world. If you aren’t chronically ill and have no issues digesting your food then you function well. If you are able to do the types of exercise and recreation that you enjoy as well as get through everyday chores without pain then you perform well.

For those quantitatively minded folks who enjoy experimenting with their bodies, AKA biohacking (ugh I find this term pretty nerdy) then getting your body composition measured is a great way to get some before and after metrics for whatever you are implementing into your life.


About the Author

Michael Gregory is a former U.S. Marine who helps weekend warriors and fit pros get ready for their next challenge be that a fight, an intense military school, or beach season. You can find him in the real world on a wave in Bali or eating a cheesesteak in Philly. For more by Michael check out his Instagram @composurefitness.