What is body composition?

My body years ago vs now… I have put on a considerable amount of muscle and shed some fat through many phases of building and cutting. These big changes take time!

If you regularly consume fitness content, it’s likely you have seen a transformation photo where someone has toned up quite a bit, but is the same or higher weight in the after photo. How is this possible? The person has changed their body composition!

Body composition refers to the percentage of each type of tissue a person’s body is made of; usually bone, muscle, and fat. Generally, when the term is used in the fitness industry, we’re talking about percentage of body fat. When someone says “body recomposition”, they’re usually talking about losing fat and gaining muscle.

Today, we’ll talk about how body composition is usually measured, and why we even care in the first place. Is your fancy bathroom scale that claims to measure body fat percentage worth it? Should you spring for a test that will give you a detailed readout? Let’s dive in!

Why is how much fat someone has important?

Knowing the ballpark your body fat percentage lies in can be helpful. It is unproductive to be at an extremely low or high body fat percentage. Our weight doesn’t always tell us if we are at a healthy level of body fat.

If you have ever heard of someone being “skinny fat”, then you know this!

BMI, or body mass index, uses a person’s height and weight to determine the weight category they fall into, but it has shortcomings. It is much better used for populations, like assessing the weight status of an entire country or state, rather than for individuals. While BMI trends can tell us if a certain population is becoming more overweight over time, for individuals, it is often misleading.

At the same BMI, an athlete will have much less body fat than someone who does not train. Women tend to carry more body fat at the same BMI as men. A person’s ethnic group will also impact how much body fat they might carry. A senior citizen is likely to have more body fat at the same BMI as a younger person.

Many of the health risks associated with being “overweight” are truly health risks from having too much body fat.

Therefore, falling into an overweight BMI can indicate more health risks for one individual than for another, and might be a poor indicator of health risk for some people. Body fat percentage will tell you much more about your potential for health risk.

The American Council on Exercise’s categorization of body fat percentages

Determining Body Fat Percentage at Home

So now that we know why it’s important to fall within a healthy range of body fat, how can we figure out where we lie within that continuum?

There are many ways on the market today to determine body fat percentage. Some are more accurate, fancy, and expensive, and some can be bought on Amazon for less than $20. For health purposes, it is really only important to know what rough category of body fat levels you fall into, so I urge you to go with one of the simpler methods.

BIA Methods - Flowing with the Current

Many bathroom scales available these days advertise the ability to read body fat percentage along with weight. To do this, they use bioelectrical impedance analysis (BIA). A harmless, painless current is passed through the user’s body, and the resistance of the tissues it passes through is measured. Muscle holds more water than fat does, and is thus easier for current to flow through. The amount of resistance the current encounters is used to calculate what types of tissues the person’s body contains.

These scales are accessible, relatively inexpensive, and can be used in the privacy of one’s own home. They can be used frequently to monitor weight and body composition, so it’s easy to collect a lot of data points over time. They also require no training or skill to use.

However, there is a lot of room for error in the measurements provided by these scales. Studies across a few brands of scales have shown them to have 21 to 34 percent margin of error. This is partly due to inherent error in the equations the scales rely on to convert resistances to a body fat percentage.

Error is also introduced when users don’t follow consistent protocol around use. Working out or having a meal in the 3 hours before using the scale can skew results, as can having calloused feet! It’s important that the conditions around use are as similar as possible each time you take a measurement to ensure consistent results. It’s also important that you use the same exact scale each time to measure your body fat, as even a different machine of the same brand and model can be calibrated slightly differently.

The verdict on these home-use scales: though they likely won’t give you your exact body fat percentage, the measurements can be useful in relation to each other to determine the direction you’re going in. It’s far more useful to know whether you’re gaining, maintaining, or losing fat than to know an exact number at an instant in time.

Many health club settings also offer body composition analysis powered by BIA. These machines, often from the brand name InBody, have a handheld component that allows them to pass more currents through the body for a better reading. However, they suffer from the same flaws that home models do.

Inconsistent usage can skew the results, as can use of different machines. There is also still the error introduced by the imperfect equations used to calculate body composition from the measurements taken.

Just like with the bathroom scales, InBody and similar machines are best used to take measurements in relation to each other to measure progress, or to get a ballpark idea of body fat percentage, rather than in search of an exact measurement.

Pinch an Inch with Calipers

Calipers can also be used to measure your body fat at home.

If you’ve ever watched a fat loss reality show (because we all have to turn our brains off sometimes), you’ve likely seen a coach pull out a set of calipers to measure a client’s body fat.

Calipers are used to measure skinfolds in various areas that tend to accumulate fat, like the suprailiac fold.

Calipers are really only as accurate as the person using them is skilled. Skinfolds in various sites on the body are measured. It is important that the person measuring knows exactly where to pinch the skin to measure. Some of these sites include the tricep, the abdomen, the thigh, and the back, and the same exact area must be measured each time for precision.

The measurements taken are then plugged into one of a few choices of equations to yield a body fat percentage estimate. Some use only 1 or 3 sites, while others use up to 7! Some measurements are more accurate than others, and some are better used on certain populations.

If you’re using calipers to measure body fat, it’s a good idea to have the same person take the measurements each time, so the measurements will be consistent. It is possible to get an incorrect measurement due to pinching too much or too little skin, or accidentally not measuring at the same exact site each time. It is recommended to take the same measurement 3 times and then average it, and it’s also important to take all measurements on the same side of the body.

An advantage that calipers have over some of the other measurement methods is that specific sites where fat accumulates are measured individually.

The BIA method can’t tell you where on your body the fat is, which is a disadvantage due to not all fat stores having the same impact on health. Abdominal fat in particular has been shown to be more dangerous to a person’s health than fat stored elsewhere, like the butt and thighs.

Even if the equations used are imperfect and will not yield a completely accurate body fat percentage, the measurements taken can be useful. Single measurements taken over a span of time can still give us information about fat gain or loss in specific areas. For example, a reduction in the abdominal or suprailiac skinfold thicknesses over time can indicate loss of belly fat!

A reduction in belly fat, even if total body fat doesn’t change much overall, can reduce health risks quite a bit!

Though calipers are an imperfect measurement tool, their portability and accessibility make them popular in fitness settings. When a trained professional uses calipers, there is a +/- 3% margin of error.

Using your Peepers - Eyeballing Body Fat Percentage

Visual body fat percentage chart - female

When it comes to home options, there is one more way to assess body fat that is entirely free.

You can visually assess the amount of body fat you carry. This method requires no equipment and though it is the least accurate, it is still worth mentioning.

All you need to do is find a reputable chart depicting individuals of your gender at different body fat percentages, and then find which one looks most like your body. This can let you know which category your level of body fat falls into, generally within 10%.

This method is ripe with potential for error. As any person who has struggled with body image can tell you, we’re not always the most accurate assessors of our own bodies. You may see your body much differently than it really is, and believe yourself to be at a much higher or lower body fat percentage than you actually are.
Another shortcoming is that only one example of each body is represented in most of these charts, so if someone holds their fat in different parts of their body, they may not have an accurate idea of their own body fat percentage. For example, if a woman is 20% body fat, but tends to hold her fat in her abdomen, she might believe she is over 25% because she can’t see her abs at all. Another woman could be hovering around 25% body fat, but believe she is much lower due to holding all of her fat in her legs and butt, while having some definition in her abs.

We also don’t know how the body fat percentages for the individuals in the chart was determined. As we just discussed, every method of measuring body fat has its inherent flaws, so there is no way we can know for sure that the person shown on the chart as 15% body fat is actually 15% body fat.

Though visually assessing body fat percentage is a very loose measurement, it can be helpful in determining what “category” of body fat level you fall into. This is really what’s important here. Knowing whether you may carry too much or too little body fat can help you make adjustments to prevent disease and injury. Knowing the exact number is just a fun fact and has little implication on your health.

If you’re a female with visible ab veins and look like your skin has been shrink-wrapped to your body, it’s safe to say that you’re either right at or below the “essential fat” category threshold. This can be useful, as this hypothetical woman could be a physique competitor with a high amount of muscle mass that puts her BMI into the overweight category! So having this extra measurement can be somewhat of a sanity check for BMI.

Likewise, if a person is very light, but has no visible muscle and some “pinchable” fat, they could fall well within a healthy BMI range, but have higher body fat than is optimal for their body.

Taking a look at this chart and seeing where you may fall can help you determine if you should make changes in your lifestyle to lose or gain fat for better health, but it will not give you an exact number.

Other Methods of Body Composition Analysis

Underwater Weighing

One of the most accurate, but least accessible ways to measure body fat is via hydrostatic underwater weighing (HUW).

This method, generally only found in laboratory and clinical settings, uses water to find the density of a person’s body. The person is weighed on dry land, and then again after they have exhaled all air from their lungs and been lowered into a tank of water. The difference in these two weights shows how much they float, and thus can be used to determine how much fat they have, as muscle has a higher density than fat and “sinks” while fat “floats”.

HUW has a small margin of error, at +/- 1.5%, but again, it is prone to operator and protocol inconsistencies.

If someone fails to exhale all air from their lungs before being lowered into the water, they will float more than they should, and their body fat will appear to be higher than it is. Other things, like a recent workout or meal can also impact results.

Like BIA methods, HUW also does not indicate where on the body fat is stored.

This method is still used in scientific studies and considered sound. One of the biggest disadvantages is that it is unlikely that a person will have consistent access to this method for tracking body fat percentage changes over time. The prohibitive cost and scarce access deters frequent testing, making this a less desirable option for the everyday user.

Air Displacement - BodPod

A subject sitting in the BodPod - if you’re a space fanatic, maybe this is the test for you!

Where HUW uses water displacement to find densities of a person’s body, the BodPod uses the similar principle of air displacement.

A person is put into an air-filled chamber, and changes in the pressure of the chamber give information about how much space they take up, and thus the density of their body.

For some, this is a friendlier option than HUW because they aren’t required to empty their lungs and then go underwater, which can be panic inducing.

BodPod seems to be more commercially available and less involved than HUW. Some universities and wellness centers have a BodPod that people can use for a small fee, which seems to be $20-40 on average from my online sleuthing.

BodPod’s readings can be made less accurate by things such as hair and facial hair, moisture, and type of clothing worn. Like most methods of measuring body composition, eating or exercising right before the test, along with changes in hydration since the last test, can make for inaccuracy. It also has the disadvantage of not telling us where the fat is located on the body.

The margin of error is generally 1% to 2.7%, but again, operator errors and inconsistencies can make the test less accurate.

DEXA Scans

Another popular, but often inaccessible, way to measure body fat percentage is a DXA scan.

Also called DEXA, the Dual X-Ray Absorptiometry sends two x-ray beams through the body to analyze the density of bone, the amount of lean tissue, and the amount of fat someone has.

This method is mostly available in lab or clinical settings, and can have hefty fees associated, so for many, it isn’t a viable option for regular use. There is also some exposure to radiation, making it a less healthy option for certain people. It is recommended to keep the number of DEXA scans under 4 per year to avoid excess exposure.

That being said, DXA scans have some advantages over other methods. They can tell a person where they store most of their fat in their body. As mentioned above, excess fat stored around the organs and in the abdomen is more of a health risk than fat stored elsewhere. Another advantage of DXA is the added benefit of getting a bone density reading, which is helpful for determining your risk for osteoporosis and osteopenia.

It is less intimidating than HUW and BodPod for people who dislike enclosed spaces. The person being scanned lies on a table, as an arm suspended above the table scans their body.

The accuracy of DXA scans vary based on pre-scan protocol - you should be well-hydrated before your scan and avoid eating in the 3 hours before - but in general, the error margin is relatively low, around 3%.

So, what’s the verdict? Comparison of body composition analysis methods:

Now that we have covered most of the methods commonly used to assess how much fat a person has, you might be overwhelmed and wondering which one is the best.

My answer is an ever-annoying “it depends”.

The best way for you specifically to measure your body composition really depends on why you are looking for that information. If you are looking to know the exact number, you likely want to know this as more of a fun fact than anything else. In that case, go with underwater weighing or a DXA scan. These will get you close to your exact body fat percentage.

But knowing your exact body fat percentage won’t necessarily help you gauge your health risk or progress. If a person is 15% body fat versus 17% body fat, they will likely see little difference, and it might just be another statistic to obsess over.

What is much more important is being aware of the general category your body fat percentage puts you in. Knowing whether you have too much fat and fall into the obese category, or whether you have too little fat and are below or at the essential fat threshold, can be important for determining if you are at greater risk of poor health. Loosely tracking gain or loss of fat over time can help you determine whether your current habits are helping you reach your goals.

For most of the clients I work with, it is best to have a general estimate of where your body fat falls on the spectrum.

Knowing the exact number, though fun, is unnecessary, which is why I recommend using one of the at-home methods. Regular, consistent use of a body-fat-measuring scale or calipers is the best for this purpose, coupled with using a visual chart for a sanity check.

The takeaway: while useful for determining whether you are at a healthy level of body fat, knowing your exact body fat percentage is unnecessary. Don’t waste your time or money on fancy measurement methods unless it is really really interesting to you!

How to Measure Body Fat - How Various Body Composition Tests Stack Up

What is body composition?

Why is how much fat someone has important?