Fitness, Weightloss

Understand how to measure your body fat

Most of us have heard of body mass index, or BMI, a formula that determines whether you are at a healthy weight for your height.

What BMI doesn’t tell you, however, is your body composition — percent fat and lean tissue — which is equally important in determining your risk for health problems such as cancer, diabetes and heart disease.

In fact, some people with a normal BMI actually have a high percentage of body fat, putting them at risk for the same serious health problems as people who are obese. Conversely, people whose BMI indicates they’re obese may not have much excess body fat at all.

What’s more, where your fat is stored on your body can affect how damaging it is to your health.

Upper body obesity — your waistline — increases your risk for chronic diseases more than lower-body obesity — around your hips. Generally, the acceptable waistline for women is 35 or fewer inches and for men, 40 or fewer inches.

So what is the best way to better understand body composition?

It can be assessed in any number of ways, including:

  • Hydrostatic (underwater) weighing. During underwater weighing, you’re seated on a special chair and submerged under water. Because bone and muscle are more dense than water — and fat, less dense — the more you weigh, the lower your percent body fat. This method, currently considered the “gold standard” in percent body fat measurement, is usually available at colleges or universities.
  • Skinfolds. This method is the most widely used body composition testing method for assessing percent body fat. Equipment used for this assessment includes a skinfold caliper. A skinfold caliper is designed specifically for simple accurate measurement of subcutaneous tissue. Either a seven- or three-site skinfold may be assessed. This assessment is often performed at fitness clubs, sport and exercise physiology labs, hospitals and schools.
  • Bioelectrical impedance analysis. By standing barefoot on metal foot plates — or using a hand-held device — an undetectably low voltage electric current is sent up one leg and down the other. Since fat is a very poor conductor of electricity, a lot of fat will impede the current more so than a lot of lean tissue. By measuring the resistance to the current, the machine estimates the percent body fat. This method is widely available in health and fitness clubs. St. Charles’ dietitians also have one available.
  • Dual energy X-ray absorptiometry (DEXA.) A new technology, DEXA uses two X-ray energies to measure body fat, muscle, and bone mineral. When having the scan done, one must lay still in the supine position on what looks like an X-ray table. It takes approximately 12 minutes for the computer software to produce an image of the tissues. The results may be viewed as whole body estimates of body fat, muscle, and bone mineral as well as regional body estimates. This method is typically available at universities and research facilities.
  • Bod Pod. Instead of using water to measure body volume, the Bod Pod uses air displacement to measure body volume. Measurement time takes roughly 5 to 8 minutes per individual. Oregon Health & Science University has one that occasionally comes to Bend (usually the Athletic Club of Bend.)


General body fat percentage categories

Classification Women (percentage fat) Men (percentage fat)
Essential fat 10 – 12% 2 – 4%
Athletes 14 – 20% 6 – 13%
Fitness 21 – 24% 14 – 17%
Acceptable 25 – 31% 18 – 25%
Obese 32% + 26% +

*Body mass index (BMI) categories

BMI Weight status
Below 18.5 Underweight
18.5 – 24.9 Normal
25 – 29 Overweight
30 and above Obese

*To calculate your body mass index (BMI) or Fat Percentage contact a local Personal Training Facility.

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