Body Fat Percentage

What Body Fat Percentage Measures

Body weight breaks down into two broad compartments: fat mass and fat-free mass, the combined weight of everything that isn't fat, including muscle, organs, bone, and water.^[4] Body fat percentage is simply fat mass expressed as a share of total weight. Unlike BMI, which is calculated from height and weight alone, body fat percentage tries to estimate the actual tissue composition underneath that number.

How It's Measured

DEXA (dual-energy X-ray absorptiometry) is the method researchers most often treat as the reference standard, since it scans the whole body and separates fat, lean tissue, and bone directly. A 2022 study comparing DEXA, bioelectrical impedance analysis (BIA), and skinfold calipers in young athletes described DEXA as the more accurate device for assessing fat mass, but noted it's costly and not accessible to most institutions.^[1] The same study found BIA, the technology behind most smart scales and handheld analyzers, "significantly underestimates the fat percentage," with skinfold calipers coming closer to the DEXA numbers.^[1]

Device quality matters here. A separate 2022 study found that higher-end, multi-frequency BIA units correlated closely with DEXA (R² ≥ 0.89 for fat percentage), which points to BIA accuracy varying by device rather than being uniform across every smart scale on the market.^[2] Skinfold calipers, for their part, depend heavily on the technique of whoever is pinching the caliper, so results can shift between two people measuring the same person.^[1] No single method is free of tradeoffs. It's a choice between accuracy, cost, and how portable the equipment is.

Why People Track Body Fat Percentage

Because body fat percentage separates fat mass from the rest of body weight, it can move independently of weight or BMI. Someone's weight can hold steady while their fat and lean mass shift in opposite directions, which is part of why researchers use it alongside, not instead of, other body composition measures.

Sex is one factor that shapes both how much fat a body carries and where it's stored. A 2018 study of adults with overweight or obesity found women had a higher percentage of total fat mass than men and carried more of it in the lower body, while men carried more fat around the abdomen and more visceral fat specifically, independent of age and BMI.^[3]

How Go Go Gaia Tracks Body Fat Percentage

Go Go Gaia doesn't estimate body fat percentage itself. If you use a smart scale or other device that writes to Apple Health, Go Go Gaia syncs that reading automatically through HealthKit, then charts it as a trend alongside your cycle phase and other biometrics.

What the Research Shows

The 2022 comparison study in young athletes is a useful illustration of why the same person can get three different body fat numbers depending on the method. DEXA, BIA, and skinfold calipers each produced different readings on the same group of subjects, with BIA underestimating fat percentage the most and skinfolds falling between BIA and DEXA.^[1]

The 2018 body composition study also found that overall fat mass and where that fat sits on the body are separate variables. Two people can share a body fat percentage and still have very different amounts of visceral versus lower-body fat, a distinction covered in more depth in Visceral Fat.^[3]

Related Terms

Frequently Asked Questions

Educational information based on published sources. Not medical advice. For personal concerns, please consult your doctor.

What's the most accurate way to measure body fat percentage?

DEXA (dual-energy X-ray absorptiometry) is generally treated as the reference method in research, but it requires specialized, costly equipment that isn't accessible to most people. A 2022 comparison study in young athletes found that bioelectrical impedance (the technology in smart scales) tends to underestimate body fat percentage compared with DEXA, with skinfold calipers landing in between. A separate 2022 study found that higher-end, multi-frequency BIA devices correlated closely with DEXA (R² ≥ 0.89), so accuracy depends heavily on which device is used.

Do men and women store body fat differently?

A 2018 study of adults with overweight or obesity found women had a higher percentage of total body fat mass than men and stored more of it in the lower body, while men carried more visceral fat and more of their fat around the abdomen, independent of age and BMI. Fat amount and fat distribution are two separate things a percentage alone doesn't capture.

How does Go Go Gaia track body fat percentage?

Go Go Gaia doesn't estimate body fat percentage itself. If you use a smart scale or other device that writes to Apple Health, Go Go Gaia syncs that reading through HealthKit and charts it as a trend alongside your cycle phase and other biometrics.