All entries for October 2012

How Body Fat Percentage Can Trick You


One of the most commonly used measures in fitness is body fat percentage. Men and women alike look at this number as the 'all powerful indicator of health,' and often, put too much stock into this single value. While body fat is an important measurement, due to its correlation with overall health status, there are some important facts to understand before putting too much stock into body fat percentage alone.

First of all, most body fat devices are not very accurate. Many people have scales at home that also tell body fat percentage through information gathered through something called "bioimpedence." This technology works by sending an impulse through the body via the feet and calculating the mount of time it takes the impulse to get through the body and back again. The shorter period of time it takes to get back, the less perceived body fat there is, and vice versa. The science behind this is that muscle has more water than fat, and is also conductive. Thus, the impulse can travel quickly.

The problem is that hydration plays a major role in this reading. A person who is not adequately hydrated may show a higher body fat percentage than is actually accurate, and a person who is overly hydrated might get a number too low. In fact, if you woke up, checked your body fat, and proceeded to drink two liters of water and re-test your body fat, you might be shocked at how different the readings actually are. The handheld devices at most gyms work in a similar manner.


The calipers at your gym have an estimated 3.5% error built in to them, which can go either way. This means that your reading could be off by 7%! This measure can be even more inaccurate if it is taken by an inexperienced reader due to individual variance between testers. 


The gold standard method is considered underwater weighing, which is rarely seen in commercial fitness centers due to its cost and lack of practicality. So, this leaves DEXA (Dual Energy X-ray Analysis) and ultrasound technology body fat devices to get the most accurate results. At Revolution Training Centers, we use an Ultrasound body fat mechanism which works the same way as an ultrasound at the hospital. These are the two best methods to use if you have the opportunity to use them. 

When you get a device that is actually accurate, there are a few things that you are going to want to remember.

Never compare your body fat percentage with someone of the opposite sex! Men need about 3-5% body fat to survive, while women need 12-15% for child bearing. Women with lower body fat percentages are usually either very unhealthy or professional athletes.
It is better to look at actual weight derived from fat than body fat percentage itself. – For example, a 200 pound person with 20% body fat has 40 pounds of fat. If that person loses 20 pounds, and they remain at 20% body fat percentage, they now have 36 pounds from fat. Even though the percentage did not change, the amount of body fat decreased by four pounds, which is far more indicative of the positive changes that are occurring than the actual percentage itself.


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