Sometimes, the accuracy of health tracking is overrated

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About three years ago, a doctor told me I needed to lose belly fat. She didn’t care about my lower belly fat. She said as she pressed me: This was subcutaneous fat. What she wanted was for me to target about five pounds of fat loss above my belly button because that’s where visceral fat lives. No weight loss. She said my BMI and weight were fine. I needed fat Losing because I had high cholesterol and a slight elevation of liver enzyme. Due to my diagnosis of Polycystic Ovary Syndrome (now known as… Polyendocrine metabolic ovary syndrome), was convinced that type 2 diabetes was lurking just around the corner unless I immediately fixed my body composition.

She suggested that I invest in a smart scale, as well as stick to a plant-based diet. I ignored the latter (and a few months later, changed doctors after she recommended a questionable podcast about the diet). But I started to take smart scales more seriously, and began a journey of frustration that lasted several years.

Smart scales use a method called bioelectrical impedance analysis (BIA) to give you a breakdown of body fat, lean mass, and bone mass. (Some high-tech smart scales include others, but it depends on the device.) The bottom line is that a weak electrical current is sent through your body. Fat, muscle and other types of tissue have different levels of conductivity, so depending on the resistance measured, the algorithm then estimates how much of each you have. It is more accessible to consumers than other clinical methods, but it can be significantly inaccurate. It is very easy to take two BIA measures and get completely different results.

Case in point, this morning I stepped on three separate smart scales: two from Withings (one that measures just through your feet, the other has a more advanced segmented body analysis), and a third from a company called Twin Health. When I go for my monthly follow-up with the doctor, I’m measured by the InBody scale, which is a fancier version of the smart scales people have at home. Two weeks ago, I went to a sports clinic for my first dual-energy x-ray absorptiometry (DEXA) scan, which shoots low-energy X-rays through your body to provide details about your body composition, including bone density. It is often considered the “gold standard” in clinical settings. None of these devices gave me the same body fat percentage.

In fact, here are my most recent readings for each metric:

I certainly couldn’t take all of these measurements on the same day, so some variability is to be expected. However, they were all taken within two weeks of each other, after fasting, and first thing in the morning. All of these devices claim some degree of accuracy. Withings claims its BodyFit scale technology — which includes a retractable handle and a total of eight electrodes — Underwent an internal clinical study of 80 participants and found a 99 percent association with DEXA scans. Let’s say the DEXA scan is the most accurate. I’m seeing a discrepancy of 5 to 12 percentage points between it and other devices. My highest and lowest readings differ by 17 percentage points. This is it prominent difference.

This is just one measure. My metrics are on lean mass (everything but Fats) also vary greatly. DEXA, Withings BodyFit, and InBody analyze your body composition based on body parts, such as your torso, legs, and arms. Those readings also Varies by 5 to 8 percentage points. Some also estimate bone density and visceral fat. Do you think my measurements have some big discrepancy there too?

For example, a DEXA scan indicates that my bone density is very excellent and that my skeleton makes up about 4.1 percent of my total body weight. Withings says 3.7 percent. On a scale of 1 to 20, the Withings scales rate my visceral fat at 1.9 and 2.1, respectively. (1 to 12 is good, 13 to 20 is high risk.) InBody’s estimate is 14. My DEXA scan says I have 1.24 pounds of visceral fat, and ideally, I’ll get that number down to 1 pound or less.

Am I good? Honestly, it depends on who you ask. I’m sure most fitness influencers would say I’m overweight and in desperate need of tone and shape. Both DEXA and InBody gave me a C in my body composition. Ten years ago, I probably would have had massive health anxiety and struggled to find which of these devices were the “most accurate” and which numbers were the “healthiest.”

The real truth is that it doesn’t matter that much.

I do not have long term DEXA results. Those scans are beloved (ranging from $75 to $300 per person), and in general, it’s only recommended to take them every three to six months. But the scan was something I did to prove a point: the accuracy of these devices doesn’t matter as much as the accuracy of these devices does Consistency. DEXA scans are highly accurate, with a clinical margin of error of about 1 to 2 percent — but it also depends on the facility you go to, the calibration of the machine, and your hydration levels. The first DEXA scan evaluates where you are. Follow-up scans are where you start seeing useful data about whether you’re progressing or not. This is correct He turns a blind eye From the body composition method you choose – whether it’s an expensive clinical measurement or a cheaper smart scale you can get during the Prime Day sale. As long as each method is “inaccurate” with roughly the same margin of error every time, the most useful data it provides is your long-term trends.

Again, none of these devices scored the same numbers for me. Even something as simple as my weight can vary by one to three-tenths of a pound, controlling for all other factors. But what are all of them? an act What I was doing was telling the same overarching story with my directions. Body fat and visceral fat were uniformly reduced by a significant amount. The percentage of fat-free mass remained constant or increased slightly. Among methods that measure skeletal muscle, this has declined slightly. My bone density remained the same. Overall, these are all signs that my treatment plan is working and point to the same general recommendations: prioritize rebuilding lost muscle, continue to monitor side effects, review my blood tests every three months, and continue to follow up until my doctor is happy with where I’m at.

This concept also applies to other wearable devices, such as smartwatches and basic fitness trackers. Daily numbers don’t mean nearly as much as your weekly and monthly trends. If you want to move more, it doesn’t matter if your Apple Watch says you’ve taken 9,000 steps and Whoop says you’ve taken 8,000 steps. Worrying about which is “more right” misses the point entirely. What matters is whether whichever tracker you choose measures the same mile distance of approximately the same number of steps (or GPS distance) every time.

There are nuances to this. I started taking body composition analysis seriously three years ago because my doctor scared me. Since then, I’ve tried about eight different scales and body composition techniques with varying degrees of sophistication. Until I had a DEXA scan, I never had a reliable sense of my body fat percentage. I still kind of don’t. Here’s what I know: My body composition did not respond to conventional lifestyle interventions. Turns out I have insulin resistance. This makes It is easier to put on fat, which in turn increases insulin resistance. I never learned that from any BIA tool! Focusing on any single metric—be it a wearable device, scale, or blood test—has never been the key to uncovering metabolic dysfunction. I was never going to improve my way out of unlucky genetics.

In terms of health and fitness, I felt better. I also felt pretty bad. All my numbers now paint a very mixed picture. I could get lost in the weeds if I’m not careful. But the general trend? I’m on a better path than I was, and that’s what’s most important.