A hundred ways to check bodyfat

You're working hard. Is it paying off?

Your standard bathroom scale has an answer. But it's not too helpful if you're adding muscle. The extra beef adds weight, even when you're cutting fat. 

This effect can work in the opposite direction too. Ever kid yourself that your extra weight came from imaginary muscle gains? You just hallucinated the non-alcoholic version of "beer muscles". 

So you decide to measure body fat instead. Good thinking - fat level is an important overall gauge on your medical health. And then you realize there are many ways to check.

There's only one way to measure with 100% accuracy - weighing the carcass during autopsy. Most test subjects decline, for obvious reasons. 


Walking through them all, in accuracy order:

  1. Clothing fit - nothing much to this one. Do your clothes fit better?
    Not precise, but it can be pretty helpful.
  2. BMI  - standard formula using your height and weight. Quick and easy, but confuses fat and muscle the same as scales. Rates some fit people as obese.  
  3. Body composition scales (bioimpedence) - Runs electric current between your legs (scale) or arms (handheld version). The more resistance, the more fat (fat conducts less electricity). It's convenient, but inaccurate (the electricity bypasses pockets of fat). Most bioimpedence measures secretly use BMI (try entering a different weight and watch bodyfat change!).
  4. Tape measure - A definite step up, particularly with the Navy Method (comparing waist and neck). The biggest problem? Different people store fat in different spots. Not everyone puts weight on their belly.
  5. Near Infrared Interactance (NIR) - Shines light into specific body parts (like biceps) and measures how much is reflected. Fat and muscle reflect differently, but the overall effect is less accurate than skinfold measurement.
  6. 3d Body scan - Builds a computerized 3d model of your body and works as a more sophisticated tape measure.
  7. Calipers - Measures skin pinch thickness across a few locations. Starting to see some real accuracy.
  8. Bodypod (air displacement plethysmography) - Measures your size by pushing air around your body. Combines with weight to calculate density. Builds bodyfat % by building on fat's lower density. 
  9. Total body electrical conductivity - Similar to bioimpedence. An electromagnetic coil drives electrons through your entire body. Because this current runs everywhere, it's far more accurate.
  10. Hydrostatic weighing - This was considered the gold standard and is still pretty good. Weighed on a normal scale and then underwater to determine overall density. The equation relies on fat weighing less than muscle. Sophisticated versions even measure the air in your lungs with helium. Unfortunately, varying bone and muscle density can throw readings off. And hydration also affects results too.
  11. DEXA - DEXA applies two different kinds of X-rays. The process checks how much of each type shines through your body and builds this into a fat percentage in a grid across your body. Similar issues as with underwater weighing, but also depends on the manufacturer's equipment/software. DEXA seems to have the most trouble with abdominal fat, possibly because the software assumes we are flat like gingerbread men. Also, you're exposed to X-rays.
  12. Four compartment analysis - Breaks the body into four components: mineral, fat, protein, and water. It combines multiple methods: underwater weighing, DEXA, and deuterium dilution. And still, it's difficult to prove exactly how accurate this is.
  13. Autopsy - no fun at all. : )

My favorite? Optical bodyfat measurement. It's convenient and accurate (roughly around DEXA, but we're working on accuracy studies). 

If you really want to geek out, check out Methods of Body Composition Analysis Tutorial. Kind of clunky animation, but it really explains the major methods in detail.

What does it all mean?

If you're getting in shape, measure your progress with bodyfat. Pick out the most accurate method you can stick with (price and convenience) and stick with it. Some of the less accurate measures will at least keep reasonably consistent.

The payoff is in finding out what works for you. Doesn't matter if you're unicycling, eating watermelons, or just wishing for it.

If you feel good, and you're dropping fat and adding muscle, just stick with it.