When it comes to monitoring body fat, the scale leaves a lot to be desired. Weight alone doesn't indicate fitness—the needle moves for fat and muscle alike. Even for those not battling the bulge, body fat testing can be a nifty way to measure training progress and overall body composition. But not all methods measure up. Read on to learn about the madness behind the measurement—and whether it's worth the trouble at all.
The "biggest" (most inconvenient) and "best" (most expensive) methods
Researchers have debated the ideal way to measure body fat for years, testing, comparing, and refining formulas all to determine the best approach. For the general public, however, it will likely come down to availability—most people will simply have to use whichever of these systems is closest to them (that is, unless they want to get very DIY). And since most body fat testing formulas are based on regression models, the further a subject is from an average height and weight—often young individuals of average weight—the less accurate their results will tend to be.
It's all water weight: Hydrostatic weighing. Hydrostatic weighing is one of the oldest methods still in use, tracing its roots back to the principals from Archimedes' famous bath. People sit atop a scale that's dunked in water, and their weight (dry and submerged) plus the amount of water splashed out is used to calculate their body's density. From there, fancy formulas are used to estimate body fat. Unfortunately, all of this can be thrown off by natural differences in bone density, hydration level, or the air left in those water-wings we call lungs.
Fat analysis is a breeze: Air displacement plethysmography. Enter the Bod Pod. This device also uses Archimedes' Principle, but with air rather than water (this makes things considerably more simple though not necessarily more accurate). Instead of exhaling all the air in your lungs and plunging into a carnival-esque dunk tank, there's just some skimpy clothing, a 15 minute time commitment, and anywhere from a $10 to $75 fee—assuming you can find a facility that owns one of these pricey machines on the web (or… a Pinterest board?).
Only skin deep: Duel energy X-ray absorptiometry. Ease of use has contributed to the Bod Pod's popularity, but for researchers it's been gradually replaced by DEXA scans, generally regarded as the most dependable method for measuring body fat (Dual Energy X-ray Absorptiometry, for those who want to sound official). While DEXA isn't without its problems (there's variability between machines, and a scan can cost $200 or more), it's generally thought to be at least as accurate as a Bod Pod and has the added benefit of being able to identify where fat is deposited in the body.
The cheapest and easiest methods
The hassle and expense of underwater weighing, Bod Pods, and DEXA precludes all but the most curious from getting their body composition tested. For those with a more idle interest (and a mean online shopping habit), there are a number of cheaper, at-home testing methods.
You'll get pinched: Skinfold test. The skinfold test is an old standby where calipers (think of them as a cross between giant tweezers and a geometric compass) measure several body parts to see how much fat is lurking beneath the skin—and where. The results are plugged into any number of equations that estimate body fat using population averages (these equations have been popular for decades, but in an effort to improve reliability many more have been devised). This is fine for epidemiological studies (or at least used to be), but isn't terribly helpful for individuals looking to longitudinally measure the effect of, say, dropping beer from a diet. Another huge factor to consider is the experience of the person performing the test—aka pinching with those giant tweezers—which can have a dramatic impact on final results.
A shocking body: Bioelectric impedance. Another popular option is Bioelectric Impedance Analysis (BIA), which is how those fancy scales at the gym estimate body fat. Electricity moves through tissues (like fat and muscle) differently, and that change in conductivity can be used to figure out relative fat mass, though it's debated if this method is more accurate than caliper use by a knowledgeable pro. While these $30 (give or take) devices can give you a decent base reading, they aren't sensitive enough to accurately detect small changes (think day to day) so any progress they register will likely be apparent to the naked eye already. Factors like hydration and recent exercise can also affect BIA readings.
Every method has its drawbacks, but what advantage does somebody have knowing their true body fat percentage anyway? So long as there's improvement on the field, track, scale, or weight room without a noticeable loss of muscle/addition of fat, that's probably positive progress. Research indicates that people are notoriously bad at gauging their own body composition, but with a little help, both the aesthetically and athletically minded can get a pretty good guesstimate. But with plenty of variability in body fat testing, it's usually best to put more energy into exercise and diet than measuring every little inch.