What is Body Composition and Why It Is Important

In over a decade of testing body composition in the lab, we’ve experienced a significant shift in our client’s education around this topic.  More and more, people in Tennessee (and beyond) are coming in equipped with the mindset that it’s not just about the number on the scale. Body composition is about understanding the intricate balance of fat, muscle, water, and bone that makes up your unique physique.

Whether your interest in body composition comes from a desire to enhance health, improve physique, or maximize performance, let’s dive in and explore why this metric matters.

What is body composition?

Body composition refers to the distribution of tissues that make up our body.  We have four primary “buckets” — typically referred to as compartments that we sort the tissue into:

1. Fat Mass: Adipose tissue 
2. Lean Mass:  Muscle and other non-fat tissues (e.g. organs)
3. Bone Mineral Content:  Minerals that make up our skeleton.
4. Water: “Now that’s what I call some high quality H2O”

An assessment of body composition will effectively sort our body by the percentage of tissue that we have in each compartment.  For example:

• 2-compartment assessment: Fat Mass vs. Fat Free Mass (Lean + Bone + Water)
• 3-compartment assessment: Fat Mass vs. Bone Mineral Content vs. Lean Mass + Water
• 4-compartment assessment Fat Mass vs. Bone Mineral Content vs. ‘Dry’ Lean Mass (i.e. Protein) vs. Water

Why is body composition important?

Accurately assessing and tracking body composition is crucial as part of a thorough health screening and risk evaluation. Understanding the makeup of our body fills in the gaps and paints a much more complete picture than a simple BMI (height/weight).  There are significant correlations between body composition and metabolic health, endocrine function, etc.

For example, understanding that a patient has elevated visceral adipose could be an underlying cause of why they are experiencing hepatic insulin resistance (insulin resistance at the level of the liver).  That patient’s blood draws and other biomarkers may reveal some borderline results such as “high-normal” values that might otherwise get overlooked. When paired with body composition data, your care team can see a more complete picture and more effectively implement interventions that will address the root cause.

How to assess body composition?

There are several tests available to assess body composition.  Choosing the right test for your scenario will depend on how your prioritize the following factors:

• Cost – What am I willing to invest in terms of money/time?
• Access – Is there a lab or equipment near me?
• Accuracy/Precision – What level of accuracy and precision do I need?
• Repeatability – Do I need to repeat this same assessment in the future to track progress or change?

3 Field Methods

When minimizing barriers to assessment such as access to equipment or cost of testing, there are several methods that can be used to assess body composition “in the field.” This could be your local gym, nutrition store, doctor’s office, or even home.  The three most popular “field” methods are:

1. Bioelectrical Impedance Analysis (BIA): Completed using a scale or handheld device that passes a low-level electrical current through the body. The device measures the resistance (impedance) encountered and understanding the differences in conduction between fat and lean tissue can estimate body composition.  (InBody, SECA, Tanita, home smart scales)
2. Skinfold Calipers: Completed by a technician that pinches skin and underlying fat and measures the thickness of these ‘skinfolds’ at specific body sites — typically the waist, thigh, triceps (women) and chest (men).  The site measurements can be added to an algorithm to estimate body composition.
3. Circumference Measurements (Navy Method): Completed by measuring body circumferences at key sites with the waist, hip, and neck being the most common.  As with the skinfold calipers, the individual measurements are added to an algorithm to estimate body composition.

3 Lab Methods

When greater accuracy is desired, it is necessary to seek out a lab with specialized equipment for assessing body composition.  The three most common “lab” methods are:

1. Dual-energy X-ray Absorptiometry (DXA):  Completed on a scanner that uses low-dose X-rays at two energy levels to differentiate between bone, lean, and fat, tissue.  DXA provides a detailed regional and whole-body analysis of body composition.
2. Hydrostatic (Underwater) Weighing: Completed by submerging the full body in water and sitting on a  specialized scale while submerged.  Based on the displacement of water and buoyancy of tissue, this method is able to measure body density which can be converted to body composition.
3. Air Displacement Plethysmography (Bod Pod):  Similar in principle to hydrostatic weighing, this method uses air (instead of water) displacement to make the experience more pleasant and improve client compliance and accessibility. Completed by sitting inside a sealed chamber while subtle changes in air pressure within the chamber are used to measure body volume (and as a byproduct — body density).

What is the difference between BMI and body composition?

This terminology is often used interchangeably, which is both confusing and inaccurate.  Here’s what to know about BMI:

BMI (body mass index): A calculation based solely on inputs of height and weight.  If you know your height and weight with a little conversion to the metric system, you can calculate your BMI based on the equation below:

BMI as a metric makes sense for large sets of population-wide data where we may only have access to height and weight, but it’s not meant to be an individualized metric.  Someone with a high BMI could be a very healthy individual with superior muscle mass just as easily as someone with a low BMI could be at risk for a variety of health complications and disease.  In these cases, we need to understand the body composition or the distribution of tissues that make up body weight to better assess health status.

Body Composition Goals

Now that we’ve covered why body composition matters and have walked through various assessment methods, let’s transition into setting body composition goals.

Setting Goals with Body Composition Data

Once you’ve received the data from your body composition assessment, the next step is using that data to set goals.  Even if you aren’t necessarily looking to lose body fat or significantly alter your body composition, having a goal and timeline for your next recheck is an important determinant to maximize the insights from the data as well as your likelihood to maintain or make progress.

As with many health metrics, it’s worth starting with the SMART guidelines for goal setting.  This means that goals set should be:

Specific, Measurable, Achievable, Relevant, and Time-bound

The way to do this is taking a general, non-SMART goal of “lowering my body fat percentage” and applying the SMART criteria to transform it into a SMART goal that might look something like this:

“My goal is to lower my body fat % as measured by DXA from 30% to 28% upon my recheck in 90 days.  This goal is relevant to my health optimization strategy as it may positively influence my lipids and reduce stress on my joints.”

Taking the time to set this SMART goal and put the follow up visit on the calendar are two small steps that have proven to make a significant difference in outcomes.  

Frequency of Testing Body Composition

One question we get asked often by clients is, “how often should I be testing my body composition?”

As with many questions the answer is “it depends” but the following guidelines are what we’ve developed over the last decade of testing:

• At minimum, it is recommended to have a body composition assessment done 1x per year as part of your annual physical.  This helps to keep up with any trends or changes that could influence your health trajectory.
• If you are implementing active interventions for body composition (nutrition plan, exercise regimen, medication, etc.) and want to gauge the effectiveness of those interventions a good recheck timeline is 3-6 months.  For fat loss focused goals, 3 months is a sufficient amount of time, while muscle building goals may want to allow 4-6 months before recheck.
• For specialized goals (physique competition, medical weight loss, etc.) or those putting a lot of time and energy into body composition change, more frequent testing can be done in 6-8 week intervals.  This more consistent testing can be helpful for added accountability and tighter evaluation of how tweaks/adjustments to your program are working (or not working). 
• It is not recommended to test more frequently than every 4 weeks.  Even the most accurate assessments will have error rates similar to the typical amount of change that can be accomplished during this amount of time.  This extreme testing frequency introduces extra “noise” due to common fluctuations in body mass, fluid retention, etc. that can be damaging to a person’s psyche while providing very little upside in terms of usable data.

Tips for Accurately Tracking Body Composition Change

Say it with me, “Same method. Same place. Same prep”  Following these three tips makes all the difference in the ability to use body composition data to track meaningful progress.

SAME METHOD

In order to assess progress or draw any conclusions from two different body composition data points, it is first and foremost crucial that those two data points were done using the same method of assessment.  We can never compare a Bod Pod test result with an InBody (BIA) test result and draw any meaningful conclusions.  The methods are assessing body composition in two very different ways, and the resulting body composition outputs (body fat percentage, lean/muscle mass, fat mass) are likely to be different.  Thus, it is highly recommended to avoid making comparisons unless both the initial and follow up body composition test were done using the same method.

SAME PLACE

Even when using the same method to track progress, it is important to consider that there may still be differences in the machine or assessment tool being used.  DEXA (DXA) scanning is a great example.  The two largest manufacturers of DEXA equipment are GE and Hologic.  Not only does the machine hardware from these manufacturers work very differently, but they also use different scan analysis software/methods and often different reference data (NHANES vs. World Health Organization). 

The same concept would apply if you got a caliper test done by two different technicians at your local gym.  If your first test was done by Sally Strong and your next test by Wendy Weak, you can imagine the results could be very different based on where the technicians pinches, how hard they pinch, etc. It becomes extremely difficult to track changes in body composition when introducing all of these variables.  We understand that there may be situations (relocating, insurance coverage, etc.) that necessitate a change in lab or provider but try to minimize changes on this front whenever possible.

SAME PREP

Now that you are using the same method of body composition assessment and going back to the same place or machine, there’s just one more hurdle to an accurate comparison — your preparation!  Some questions to consider:

Is there a fasting requirement for the assessment? 

Am I doing the assessment before or after exercise?

Does my clothing matter and if so, is what I’m wearing similar to my last assessment?

For BIA testing, did I wipe down my hands and feet the same way?

Should I do the assessment at the same time of day or for women, the same time in my monthly cycle?

These questions will vary from test to test, but the more consistency you can keep in your preparation when repeating a body composition test, the more likely you are to get consistent and comparable data to use.  This data is commonly used to drive key health decisions and evaluate training and nutrition programs that folks have invested time and resources into. It’s worth the extra diligence to assure the integrity of that data is the best it can be.

Conclusion

There’s much more we’ll cover in the world of body composition (including how to improve body composition), but mission accomplished if you walk away from this article with a deeper understanding of what body composition is, how to assess for it, and most importantly how to use your body composition data to set goals and track progress in your health journey.

For those in Tennessee (and surrounding states) looking for a lab to perform DEXA, Bod Pod, or any other body composition assessment, send us a message.  If the specific modality is not available in our Nashville lab, we work collaboratively with other laboratories and imaging centers and will be happy point you in the right direction.

References

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