What is Body Fat (%) ?

Body fat is considered an energy reserve, and deposited fat provides a number of other functions. It serves as a protective cushion and provides structural support to prevent injury to vital organs such as heart, liver, kidneys, and spleen. It also insulates the body from heat loss and extreme temperature changes and this deposits under the skin may be metabolized to generate heat in response to lower skin temperatures. Lipids yield 9 kcal of energy per gram while carbohydrates and proteins yield only 4 kcal of energy per gram. Most of the fat in food is in a form of triglyceride. Fatty acids are classified according to their degree of saturation as saturated, monounsaturated and polyunsaturated fatty acids. For these fatty acids are hydrophobic, they are transported in the blood in the form of lipoprotein.

Underwater weighing is considered one of the gold standards of body composition assessment. In this procedure, body density is calculated from body volume according to the Archimedes principle of displacement, which states that an object submerged in water is buoyed up by the weight of water displaced. Once body density has been determined, this value is converted to percent body fat through calculations.

Using electric methods to measure the body fat, it is known that electric current does not flow through body fat. So, the more fat in body, the more increase in resistance, utilizing BIA to measure. Fat is the most concentrated source of energy, and in excess, it may be harmful to health. Excess of body fat, higher than standard values adjusted to weight, is considered obesity, and it accumulates in abdomen or subcutaneously.

Body fat percentage standards differ by age group and sex, and there is no single unified standard. Below is an example of body fat percentage standards for different age and gender groups: 

Body Fat (%)
Age Female Male
10~34 20.9%~32.5% 8.6%~19.3%
35~49 23.5%~35.1% 11.8%~22.5%
50~80 24.5%~36.1% 13.8%~24.5%

Reference: Daniel P.Williams, Scott B. Going, Timothy G. Lohman, David W. Harsha, Satharnur R. Srinivasan, Larry S. Webber, Gerald S. Berenson, Body fatness and risk for elevated blood pressure, total cholesterol, and serum lipoproteinrations in children and adoles cents American journal of public health, March 1992 , Vol. 82, No.3.