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What Is a DEXA Scan and How To Boost Your Fitness

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What is a dexa scan: Woman measuring her waist



“If you can’t measure it, you can’t improve it.”


This famous quote by management guru Peter Drucker was originally used in a business context. However, it’s true for anything in life that you want to improve. Same for health and fitness. If you don't define and measure certain metrics regularly, you will never know if you are actually on the right path to achieving your goal. 

Biometric measurements such as body weight or body fat are a key area for health and fitness. In this article we take a closer look at how to measure body composition focusing on the most accurate method: DEXA scans. 

What Is a DEXA Scan?

A DEXA scan (otherwise known as a DXA scan or bone density scan) is a technique to measure bone density. 

This test basically determines how strong your bones are and if you potentially have bone loss. This could lead to osteoporosis (deterioration of bone mass, which can lead to increased risk of fracture) or osteopenia (which is characterized as concerningly low bone density but not as severe as osteoporosis). 

As a young adult you are typically not suffering from bone loss but the risk increases the older you get. However, the right nutrition and exercise (sometimes medication) can help keep your bones dense and strong.

As an interesting byproduct, bone density tests can also give us a lot of very accurate information about body composition. Two low-energy X-ray beams can give us a clear picture about the amount of bone tissue and soft tissue (muscle mass and fat) you have. We’ll go into how this works in detail later. 

Why You Should Measure Your Fitness Progress 

If you are serious about improving your health and fitness, you will have to set your goals, decide on relevant metrics, and then measure them on your way to success. 

A great analogy is hiking and navigating in the mountains. Reaching the peak of the mountain is your goal. Your fitness program is like a compass and a map. On the way to the peak, you need to regularly check landmarks to see if you are still on the right path to that peak. 

This is exactly what you do by measuring your metrics on your health and fitness journey. The quality and accuracy of your measurements will determine how fast and efficiently you achieve your goals. DEXA scans are one of the most accurate and reliable methods to determine and measure body composition. 

Different Ways To Measure Body Composition 

There are different metrics that determine body composition and there are a variety of ways to measure them. Body weight is one typical measurement but it is not very meaningful. An athlete and an obese person can have the same body weight. A more useful metric for health and fitness is body fat. 

Body fat is not categorically a bad thing. It is necessary. Our body uses fat to store energy. In addition, it serves as insulation and protection. Just too little or too much can be problematic. The latter can lead to obesity, heart disease, or Type 2 diabetes.

It is a good, even necessary practice to know and track your body fat. Here are the different ways to measure body fat related to body composition.

Skinfold Calipers

What is a dexa scan: Skinfold Calipers

The most affordable and accessible way to measure body fat is by using calipers. They can be purchased easily online and are fairly cheap. 

Typically you need to take three measurements. For women these are triceps, abdomen, and suprailiac (the abdominal skinfold, approximately 3 centimeters or 1 inch above your hip bone), while men measure their chest, abdomen, and thigh. You can insert these values in one of many online body fat calculators together with age, gender, and body weight. 

For reliable measurements you need to make sure that you always measure at the same locations on your body and also in the same condition (like in the morning right after getting up and on an empty stomach).

Body Fat Scales

Body fat scales are another affordable way to measure body fat. They use bioelectrical impedance analysis (BIA), which involves sending small electrical current through your body. Fat, bones, water, and muscle show different resistance to electrical current. Based on this, the scales estimate body fat.

This type of measurement probably will not give a true reflection of your overall body fat percentage. The current does not pass through your whole body but only up one leg and down the other. But still, it can be used as a reference point to measure a trend over time. 

Body Circumference Measurements

Body Circumference Measurements

Using a standard measuring tape to measure body circumference is probably the cheapest way to determine body fat. It is also the most inaccurate and unreliable method. It is based on the idea that certain body shapes can correspond to certain body fat percentages.

Women need to measure their waist, hips, and neck, and men need to measure their waist and neck. Online calculators for tape measures can give you a body fat percentage estimation. It is important that you always measure at the exact same locations. The tape should be in close contact with the skin but not squeeze it. And don't flex.

Dual-Energy X-Ray Absorptiometry (DEXA or DXA)

DEXA scans are the most accurate and most reliable determination of body fat. They are more difficult to access and more expensive (typically between 70,00 and 100,00 as you will have to go to specific centers or radiologists. I cover more details in a later section of this article.

Summary of Further Body Fat Measurements

There are a number of further ways to measure body fat. Most of them are either expensive, inaccurate, or simply not available (yet). Examples include: 

  • Bioimpedance spectroscopy (BIS), which is mostly used in medical research environments.
  • 3D body scanners, which are fairly new and hardly available.
  • Hydrostatic weighing, which measures water displacement when you go underwater. It’s accurate but only available in few medical or fitness centers (often not cheap). 
  • Air displacement plethysmography (also known as Bod Pod), which measures air displacement and is similar to hydrostatic weighing in accuracy and cost but more comfortable (you don't have to dive underwater holding your breath).

What Kind of Measurement Is Best for You?

The measurement that is best for you depends heavily on your goals, personal preferences, and what you have available in your area. Skinfold calipers is probably a method everybody should be able to use. 

More important than what you use is how you use it. Of course it’s great if you get an accurate measurement that reflects your true body composition. But more important than accuracy is monitoring progress between the measurements and hopefully identifying a positive trend that brings you closer to your goal. 

If the trend is not positive, then it’s still valuable as it gives you the data to make decisions for change. 

Regarding the how, it’s also important to always measure in the same way, in the same locations, and in the same state. I strongly recommend making such measurements in the morning right after getting out of bed. Measure yourself after you go to the bathroom but before you eat something. It can easily become part of your morning routine

A final recommendation is to mix different methods and execute them at different time intervals. On a daily basis you could measure body fat via a body weight scale. On a monthly basis you could use calipers, and once every six months you could do a DXA or bone density testing. This gives you more reliable results and a richer set of data to base your decisions on. This mix of methods is exactly what I do with my clients who are part of the Build Bullet-Proof Health Super Coach program. 

How Do Bone Density Scans Work? 

A bone density scan or bone mineral density (BMD) scan uses low dose X-rays to determine the density of bones (also referred to as bone densitometry). This density is an indication of the strength of bones. 

During your dual-energy X-ray absorptiometry scan, two X-ray beams of different energy levels are sent through the body. The DEXA scanner measures the amount of X-rays that pass through the body. This varies depending on how thick the bones are and the amount of soft tissue like fat or muscle. From this, doctors or radiologists can conclude not only bone density and bone health but also body fat percentage and lean mass. 

The process from your perspective is straightforward — no special preparations are needed. Ideally you are wearing some comfortable clothing. You lie down on a padded table on the DEXA scan machine after removing any metal objects like keys, jewelry, or a belt. The radiologist will arrange your body position according to a template so that future scans can be compared. Then it takes about 10 minutes to complete the scan and another 10 minutes to produce the report. 

Are DEXA Scans Safe? 

First of all, DEXA scans are an entirely painless procedure. People are often worried about the risk factors of this type of scans as they involve X-ray beams. However, only a very low-dose X-ray is deployed. 

It has been established that this amount of radiation is so low that there are basically zero health concerns. During one scan you are exposed to radiation of about the same amount of natural background radiation that you experience during three hours of normal daily living. 

What's the Result of a DEXA Scan?

The intention of the DEXA scan is to inform you about your bone density. The World Health Organization established two metrics for this: the T-score (difference between your measurement and that of a young healthy adult) and the Z-score (difference between your measurement and that of someone of your age). 

But we are actually a lot more interested in a separate result that we get from the DEXA scan. The resulting report also records your lean mass and all your body fat including visceral fat (fat between your organs) and intermuscular fat. The latter two are not taken into account when you test your body fat with calipers. Consequently, the body fat percentage as a result of a DEXA scan will be higher. 

In addition, a DEXA scan breaks down your lean mass to body fat ratio per body part. This is very useful information as you could identify things like imbalances between your left and your right upper arm. You can then include this into your training program to work on and improve this imbalance. Imbalances can often lead to injuries as one side constantly has to work harder.

DEXA scans are incredibly useful. You can make data-based decisions (like improving imbalances). These scans are not the cheapest but the value you gain from them makes it worthwhile. 

I typically recommend to do a scan once every six months for a solid “landmark" that helps you see your progress in your fitness journey. It also helps you adapt if necessary to continue steering in the right direction. 

How To Use Body Fat Measurements To Improve Health and Fitness

Patient having a checkup with the doctor

If you are serious about your health and fitness goals, you must track and measure your progress. Body fat is one of the key metrics for this. There are many ways to determine body fat, all varying in cost and accuracy. DEXA scans are more expensive but the most accurate method that we currently have available.

In all my health and fitness programs including my flagship Build Bullet-Proof Health, I recommend to mix various methods and measure regularly. DEXA scans, as the gold standard, should be done twice a year.

If you are based in or around Barcelona, Spain, we have the excellent Faixat Body Scan facility. As part of my Super Coach program, we established a partnership, in which we not only offer the scan itself but a detailed analysis of the results. 

Here is a typical example of a resulting DEXA scan report that you would receive (in Spanish, but you can get the gist). Contact us about our DEXA scan consulting offer if you want to learn more about the details and our discounts. 

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