Is a DEXA Scan Worth It?

Before my client Melissa and I started working together, she had been playing recreational competitive tennis for decades, but she was confused by a recent DEXA scan (her first ever). Despite being an overall more slender person, she was told that she was 32% body fat and that she would benefit from gaining 6 pounds of muscle and losing 11 pounds of fat. At 32%, her body fat percentage was higher than she was expecting, which was irritating and stressful. A DEXA scan is supposedly the gold standard for body composition assessment, and an MD was telling her that she was a lot “fatter” than she felt she really was.

For me, having a new client distressed by body composition testing begs the question: is a DEXA scan worth it? Or InBody? Or smart scales of any kind? Are they accurate? How should we use them? And furthermore, why do we do any kind of body composition assessment at all?

In this article, I’m going to share the science of how body composition is tested, my own recommendations for estimating your fat loss vs. muscle gain, and the rest of my client Melissa’s story! 

What is Body Composition Testing?

Body composition testing – which could include a high-tech scan like DEXA or a low-tech estimate with skin fold calipers – is an attempt to get a picture of how much body fat someone has, compared to their lean body mass (which includes muscle, water, bone, etc.). Understanding your body composition can help you make informed choices about which goals to focus on. It can also give you an idea of how you’re making progress.

Let’s review some of the common gadgets or machines used to test body fat percentage:

• Skin fold calipers – this used to be more common, but has waned in popularity thanks to the availability of assessments that have a higher-tech (and less invasive) feel. With this method, you squeeze specific sites on the skin and measure the pinched skin (the “skin fold”) with a device that looks somewhat like a hole punch. The idea makes sense, because you’re literally physically measuring the fat under the skin with a ruler, down to the millimeter. You average the measurements from several sites and plug it into an equation.
• InBody and home smart scales – InBody scanners seem to be omnipresent at gyms, and now smart scales are extremely popular at home. These types of “smart scales” use something called “bioimpedance” to assess body fat – a mild electrical current (you can’t feel it, by the way) passes through your body, and based on what “impedes” the electrical current (i.e., fat), an estimation is made on your lean body mass.
• DEXA – this is considered the “gold standard” by many people, although it isn’t perfect. “Dual Energy X-ray Absorptiometry” (or DEXA) is sort of like an MRI, but without going into an enclosed space. You lie on what looks like a hospital bed, and a technician passes a scanner over you, which takes two x-rays and measures body density – i.e., how much of your body is fat tissue, and how much of it is lean tissue. DEXA is much more accessible than it used to be – you can probably buy a package of several DEXA scans from a facility near you for less than $1,000. DEXA has some unique benefits because it measures bone density, as well – this can be an incredibly important measurement for certain people (i.e., leaner women entering perimenopause/menopause). It also looks at fat distribution, measuring where your fat is distributed across your body. It’s important to note that DEXA tends to “read” higher than other body fat measurement methods – possibly by about 5 percentage points (more on this in a moment).

There are other high-tech methods for measuring body fat, like hydrostatic weighing, but it’s unlikely that most people would do them, since you would practically need to be part of an experiment in a research facility! 

How Accurate Is Body Composition Testing?

But the big question is, “How accurate are body composition tests?” 

Which ones are the most accurate? Is it worth it to do any of them? Do they provide any useful information?

And by “accurate” do you mean getting the “right” number, or by getting repeatable results that are consistent over time even if the exact accuracy is a little off?

As it turns out, many methods of measuring body fat don’t fulfill either definition of “accurate.”

The truth is that body fat testing on individuals is pretty error-prone – by as much as 2-5% regularly (even if you’re doing it perfectly). That means that if you step on a smart scale and it tells you you’re 22% body fat, you might really be 17% body fat… or 27% body fat! You may also get a completely different result on a different day, based on your previous day’s workout or hydration. Obviously this is a gigantic difference, and it’s not helpful information for anyone.

Even DEXA, while touted as the most accurate way to get your body fat tested, is vulnerable to many of the same issues that plague other methods. Not only can hydration status wildly affect results (just as with bioimpedance), but there’s also other issues – the technician can perform the test incorrectly, the machine may not be calibrated, your food or exercise from the previous day may affect things, etc. It’s far from a perfect test. It’s not as though you can get a DEXA scan and be 100% confident in the results.

Most body composition testing is more accurate at a population level (i.e., averages), than it is at an individual level. The marketing of higher-tech tests, however, can be rapacious, giving you the impression that you are learning the real truth, seeing a three-dimensional internal view of your body with unparalleled accuracy.

The reality, however, is that every kind of body composition testing is using an algorithm or equation to estimate body fat, by comparing you to similar data from thousands of other people collected over the years. It’s not a direct measurement – it’s an estimation.

The only way to really know how much body fat you have is to be dissected, unfortunately.

Why I Don’t Recommend Body Composition Testing

Although I talk about body composition with clients all the time, I don’t recommend getting it “tested” (unless you are using the DEXA to measure bone density).

Body fat percentage is always an estimate. And often, if the (expensive, time-consuming) test doesn’t go exactly according to expectations, it can be demoralizing – especially if you’ve been working hard on your fitness and fat loss.

The culture of body composition testing can border on (or even veer into) body image obsession territory – a good question to ask yourself is, “What are you hoping to see?” Especially if you understand and accept that it is not entirely accurate, what is the value of a body composition test, ultimately?

Most of the time, I think we can be fairly good judges of what is happening with our body composition. If we’ve been improving nutrition and pants are looser, it’s reasonable to assume that you’ve lost body fat. But beyond that, do we really need to know an exact percentage? Not necessarily – but if we measure body fat percentage, I like to use data points that are more consistent, more reliable, more controllable, and more frequent than expensive lab testing.

What I Do Instead

It’s very simple. I recommend using the scale to capture weight, and a tape measure to capture specific body circumference points. You can plug the numbers into the Navy Body Fat Calculator, and this is an excellent proxy for your body fat percentage.

While it is still using an equation to predict body composition, it is extremely helpful that tape measurements tend to be more consistent and reliable measurements than other methods of charting progress.

In fact, I would argue that even if you don’t estimate your body fat percentage, tape measurements alone are one of the best ways to gauge fat loss. Of course, you have to pay a lot of attention to getting the tape level and measuring in the same spots every time (you can do it in a mirror to help yourself). But the nice thing about an assessment being free and at home is that you can do it frequently, to make sure that you’re at least collecting reliable, repeatable results. You can “throw out” an outlier measurement, instead of agonizing over it because you spent hundreds of dollars to get it at a facility.

But even beyond that, I encourage clients to ground themselves in the knowledge that they will physically be able to tell when they are losing fat and gaining muscle. Of course, it is hard to be objective about ourselves, and everyone struggles with bad body image days. But it is very easy to be objective about pants getting too loose and needing to buy new pants.

Possible Upsides?

I think I’ve been clear that I don’t love body composition testing. But to be fair, I think that the best use of body composition testing is to introduce the concept of body composition to someone. Many people don’t know that their body is composed of both fat mass and fat-free mass, and that the goal of weight loss is not just to lose weight, but to lose body fat. Education around body fat percentage hopefully leads to a better understanding of lifestyle interventions like strength training.

I think that body composition testing can especially serve as a wakeup call for people who aren’t as lean as they think they are, even if the number aren’t entirely accurate. Because over two-thirds of the American population has overweight or obesity, having a healthy-range BMI can lull some people into a false sense of security, especially in their 40’s and 50’s as age begins to affect lean muscle mass. A body composition test can jolt someone into making a lifestyle change and start strength training (like my client Melissa, who was only playing tennis). While it could be argued that this most benefits lean people who want to get leaner and stay healthier (vs. the other two-thirds of the population), it can still be beneficial at an individual level.

But once I have an ongoing relationship with a client, I don’t necessarily recommend getting repeat InBody or DEXA scans, unless they’ve already bought a multi-session package. Because of the error issues and the infrequency of measurement (especially for lean people who are not going to lose significant body fat), I usually recommend just switching to weighing and measuring to gauge progress. But if someone has a long-term commitment with 2-3 scans pre-purchased, I counsel them on repeating the exact testing situation as much as possible every time – even down to trying to schedule with the same tech every time. While the results may still be inconsistent, you’re stacking the deck in your favor that at least they may be more repeatable and reliable.

Melissa’s Story

As you’ll remember from the beginning of this article, Melissa (51) came to me after a surprising DEXA scan. Although she was a leaner woman, lived a healthy lifestyle, and played hard tennis several times a week, her scan came back at 32% body fat. This was much higher than she was expecting. Additionally, the MD who went over the results with her advise her that she should lose 11 pounds of fat and gains pounds of muscle.

Remember, DEXA tends to “read” higher than other body fat estimation methods, so right from the start I had Melissa do weight and measurements, and I estimated her body fat at 24% – at the top of the “fit” category, which seemed more right for her. But because she didn’t do any strength training, I supported the advice that she would benefit from building muscle and losing fat. Based on her frame, I felt that she could be healthfully leaner.

The benefit of the DEXA scan for Melissa was that it made her realize the difference between muscle and fat. When she received the initial counseling to lose 11 pounds of fat and gain six pounds of muscle, for example, she didn’t realize at first that this meant losing a net five pounds. For most people, thinking in body composition terms is an extremely foreign concept, and body composition testing can at least introduce and educate on the idea, even if the numbers aren’t entirely valid or reliable. Seeing numbers in black and white helped Melissa release that tennis on its own wasn’t enough.

Of course, we got to work right away on strength training and increasing her protein intake, and the result is that now her body fat percentage (based on weight and measurements) is 19%. But I would assume that if she repeated her DEXA scan, she would be 24-26% or so. This means that she lost about 7 pounds total, but probably 8 pounds of fat. She strength trains hard, and has even recently done her first pull-up – which is a huge first! Anyone who works on chin-ups/pull-ups knows how tough they are, and what an accomplishment that is. Right now she’s in a maintenance phase, which means we’ve raised calories since her fat loss phase, and now we’re more focused on building muscle and improving performance! She still plays tennis, and her core and shoulder strength have become so powerful that she broke her racquet strings last week with a particularly strong swing!

Here is Melissa’s story in her own words:

Before working with Rachel, I had done decades of cardio, but I was a lightweight with regard to strength training. As I was getting older, I realized my workouts had to shift to counteract torpor and weight gain.

Given her vast knowledge of fitness and nutrition science, Rachel skillfully designed a plan that accommodated my work demands, family travel and love for activities like tennis and yoga.

These gradual and feasible adjustments, like increased protein, soon yielded results. Within the few months of working with Rachel, I lost 2 inches off my waist and did my first pull-up ever. I did another parallel grip pull-up Monday to make sure it was real! I could do it – YAY! While I enjoy working toward goals, I’m surprised how fun these workouts are and how much I look forward to them. This program feels suffused with Rachel’s patience, flexibility and positive energy.

Rachel’s steady coaching has invigorated me to embrace new challenges and discard the notion that fitness decline is inevitable with age. While grateful for decrease in inches, I greatly appreciate the increase in stamina that propels me through challenges outside the gym. I can feel it whether teaching in a classroom or hitting on a tennis court, where I was recently elated to break my racquet strings due to newfound power.

I’m profoundly grateful that my DEXA experience (perplexing, dispiriting and obscenely expensive) led me to coaching!

So… is a DEXA Scan Worth It?

If you do plan to use DEXA scans (or InBody, or smart scales, etc.) as a part of your health and fitness journey, remember these tips:

• Try to always do assessments under the exact same conditions – fasted, same time of day, same time elapsed since last workout, roughly same diet, etc.
• If you can, try to get the exact same tech for DEXA each time (the tech does make a difference!)
• Particularly for DEXA, pay particular attention to bone density results – this might be the most valuable part of the test if you’re a woman over 35!
• Don’t stress over the results – listen to this episode of the Iron Culture podcast, where body composition testing is (hilariously) discussed by two very athletic bodybuilders/powerlifters who spent the weekend getting tested at a high-tech lab
• Remember that, even if you get disappointing results on a test, measurements don’t lie – back up your higher-tech scans with regular weighing, measuring, or photos as applicable
• If you’re interested, read this series of articles that explores the science (and pitfalls) of body composition testing, as well as this article

Although I don’t love DEXA scans, I understand that there are many different ways that people find their way to improvements in lifestyle and health. In Melissa’s case, it was an invitation to start strength training – which not only boosts her confidence and tennis game, but also her health and longevity! Ultimately, the “results” of her DEXA scan were very good, because of what it changed in her lifestyle!

Do you have questions about body composition? Shoot me an e-mail!