You step off the DEXA scan feeling defeated.
Despite a month of consistent workouts and clean eating, the machine indicates that your body fat percentage has increased by 2%. Your gym buddy swears by their InBody results, while another friend just dropped $100 on calipers from Amazon.
Meanwhile, you’re left wondering: which test should you trust, and more importantly, do any of these numbers matter?
Here’s the uncomfortable truth: we’re obsessing over the wrong things.
The Accuracy Illusion
First, every body fat testing method — even the “gold standard” DEXA scan — comes with a margin of error.
These machines don’t just measure your fat; they’re heavily influenced by your hydration status, which is affected by factors such as when you last ate, whether you’ve worked out recently, and even the temperature outside.
For example, muscle tissue contains a significant amount of water. When you’re well-hydrated, you’ll appear leaner on scans. Dehydrated? The numbers shift the other way.
This fluctuation means that the 2% change you’re worried about likely reflects your hydration status, not actual fat loss or gain.
Even if you control for these variables (as you should) — same time of day, same type of test (DEXA vs. caliper), same machine, same pre-test routine — you’re still looking at estimates with built-in error rates. This could be a margin of error of a couple of percentage points or more.
This means these tests are best used when multiple measurements assess relative changes over a long period of time. Not that you are 16% body fat exactly today. Or that you lost 2% body fat in a month. Points over months and years will start to reveal the meaningful fat changes (as opposed to hydration changes), as well as the best estimate of your true body fat.
The Wrong Question Entirely
Here’s what I’ve learned after years in nutrition: people often ask the wrong question entirely. Instead of, “What’s the most accurate body fat test?” ask yourself, “What will this number actually do for me?”
If you’re preparing for a bodybuilding competition where you’ll be judged on extreme leanness, precise body fat testing makes more sense.
But for us CrossFit athletes?
Your fitness is a better metric. More pull-ups and a faster 5K time are more indicative of proper fueling and improving health than any (often insignificant) change on a body fat test.
You may also be interested in your body fat percentage for aesthetics. You want to look lean. Fine enough, but the mirror already tells you everything you need to know.
You can easily determine if you’re in a healthy range (12-20% for men, 20-30% for women) by comparing yourself to reference photos.
If you want to be leaner than that, there is no percentage from any test that will change your opinion about what you see in the mirror. If you don’t like your reflection, dropping 2% more body fat according to a DEXA scan will not change that.
You need to question what you are actually chasing. What will that desired number do for you? Start cultivating that feeling in your life right now, regardless of your level of leanness, as a first step toward stopping the chase for subjective endpoints.
Measuring What Actually Matters
Instead of investing too much in body composition tests, clarify your goals and use the right metrics to achieve them.
Body composition generally trends with improvements in performance, since a lower body fat improves your strength-to-body-weight ratio. This is why fitness is a good proxy for body composition changes.
CrossFit Port Clinton
For traditional biomarkers of health, a mirror is accurate enough to assess healthy ranges of body fat. A mirror is also likely to be the most useful tool for further “leaning out” from already healthy ranges, but one must be aware that this is purely subjective territory. They may have unrealistic expectations about what a body fat percentage will do for their psychological well-being.
The person who focuses on fitness gains, real weight changes based on clothes, or just acceptance and appreciation for changes in the mirror will be healthier than someone obsessing over inconsequential (and often inaccurate) percentage points on a readout. Yes, the data is good, but it’s essential to understand its limitations and use the right tool for the right job.
About the Author
EC Synkowski hosts the Consistency Project podcast, from which this article was adapted. She’s a CrossFit L4 Certified Coach, a Certified Nutrition Specialist®, and creator of the Three Pillars Method app.