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June 13, 2012

I was talking with someone recently about body fat percentage calculation methods and thought I’d pass on the basics.

Body fat percentage

Body fat percentage is the weight of a person’s fat divided by his/her total weight.

Here are some other facts:

• body fat consists of essential body fat and stored fat: 1) essential fat is used for ongoing operation of the body, and 2) stored fat is the accumulation in adipose tissue that helps protect vital organs, especially in the chest and abdomen

• body fat percentage should not to be confused with BMI (body mass index) that compares a person’s height to weight. Devised in the mid-1800s by a Belgian polymath, BMI can incorrectly label a person obese because the equation used for calculation does not differentiate between fat and muscle, so that a short bodybuilder who weighs a lot more than an man of average weight and muscle mass can have an apparently unhealthy BMI

Here are the body fat percentage categories listed on Wikipedia, which mirrors my fitness literature:

Description Women Men
Essential fat 10–13% 2–5%
Athletes 14-20% 6–13%
Fitness 21-24% 14–17%
Just “Average” 25-31% 18-24%
Excess fat 32%+ 25%+

 

Most Accurate Measurement

Hydrostatic testing — submerging people in water — measures actual body density rather than relying on equations that predict density, which is what other methods do.

In specific, hydrostatic testing involves calculating:

“…the volume of the displaced water from the weight of the displaced water. A correction is made for the buoyancy of air in the lungs and other gases in the body spaces.”

For those of you who love the science behind a method, here’s the explanation:

“… the fat cells in humans are composed almost entirely of pure triglycerides with an average density of about 0.9 kilograms per liter. Most modern body composition laboratories today use the value of 1.1 kilograms per liter for the density of the “fat free mass”, a theoretical tissue composed of 72% water (density = 0.993), 21% protein (density = 1.340) and 7% mineral (density = 3.000) by weight.”

The trick is finding a place that offers the measurement. An article I found suggests contacting a university that has the equipment for research purposes and offers testing on the side for $50 or so.

Most Common Method

The caliper test is one in which a clinician uses calipers — which cost as little as $15 — to measure skinfolds at various places on the body, such as the triceps, thigh, waist, calf and abs. Imagine pinching your waist to see how much extra tissue there is.

The idea is to determine the fat layer just beneath the skin.  The clinician then uses an equation to turn the measurements into an estimated body fat percentage.

This test is relatively easy and inexpensive to perform, but the results can contain a fair amount of error unless the calipers, and the skill of the technician, are of good quality.

Other Methods

Air Displacement Plethysmography (ADP)

This method uses the same principle as hydrostatic testing, except that instead of being submerged in water, people are put in a sealed chamber and their body fat percentage is measured by how much air they displace.

“Body volume is combined with body weight (mass) in order to determine body density. The technique then estimates the percentage of body fat and lean body mass (LBM) through known equations (for the density of fat and fat free mass).”

Dual Energy X-ray Absorptiometry (DEXA)

This is a cool, techie method in which a whole body x-ray scanner is used to measure bone mass and soft tissue mass.

When the scans are complete, technicians use a computer to compare the images, which show the amount of fat and where it is, after which they can calculate the overall body composition.

Again, the challenge is to find  where this testing is offered. Consider calling your doctor for a referral. The price is usually about $100.

Ultrasound

This method uses sound to measure subcutaneous fat thickness. Multiple sites on the body are tested, after which the data is used to estimate body fat percentage.

I’ve undergone the caliper test, which is fast and painless. If anyone else has tried other types of testing, I’d love to know when and where you had the testing, how much it cost and what the experience was like.

So many ways to calculate body fat, so little time!

Happy working out.

From → Science

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