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Body Composition
by Dr. David Williams

One indicator of a person's current fitness level is his body composition. Body composition refers to the relative amount of fat and non fat (lean body mass) that a person possesses. To be physically fit, a person should have large amounts of lean body mass and small amounts of body fat. Lean body mass is comprised of muscle, bone, skin, hair, internal organs, etc.; anything that is not fat is considered lean body mass.

The fat component in the body is composed of essential fat and non essential fat. Essential fat is required by the body for normal cell maintenance. The body needs a small amount of fat to store fat soluble vitamins (A, D, E, and K), there is fat surrounding your nerves (myelin) that help to increase nerve conduction velocity, there is fat surrounding your internal organs that act as a shock absorber, fat acts as an insulator during cold weather to conserve body heat, and fat supplies energy during aerobic activities. So, the body needs fat, but it does not need very much. Essential fat for males only accounts for approximately 3% of their body weight. Essential fat for females is only about 10-12% of their body weight. The percentage is higher in women because it includes sex-specific fat; such as the fat found in the breasts and in the uterus. If a person does not possess adequate levels of essential fat, he or she is at risk for certain health problems. For example, that person may be deficient in any one of the fat soluble vitamins, or if it is a woman, her menstrual period may become irregular or painful, or absent altogether.

The body needs essential fat, but non essential fat can be detrimental to a person's health. The more non essential fat that a person has, the more energy that is required for that person to perform his normal activities of daily living. If a person has 20 extra pounds of non essential fat, it will be harder to go up stairs, walk around the mall, or play a game of softball. Carrying 20 extra pounds of fat would be equivalent to carrying around a 20 pound bag of dog food all day; it would tire you out after a while.


There are numerous methods of determining body composition. In the past, people relied on height/weight charts to determine their ideal weight. According to Hoeger (1988), these tables were first published in 1912 and were based on average weights (including clothes and shoes) for men and women who obtained life insurance policies between 1888 and 1905. The increased interest in exercise has caused people to have higher levels of lean body mass, making the height/weight charts obsolete. The inaccuracy in the height/weight charts in determining ideal body weight was demonstrated when a 225 pound man applied to join a city police force, but was denied an interview because he was "too fat" according to the height/weight charts. When this man's body composition was later assessed at a sports medicine clinic, it was determined that he was only 5% body fat (Hoeger, 1988). He was denied an interview because he was too fat, but in fact he was very fit.

The most accurate method of determining body composition is through hydrostatic weighing. With this method, a person is actually weighed under water. Body fat has a specific density of less than 1.0 causing it to float when under water. Therefore, a person with more body fat will weigh less when weighed under water. Although this method is the most accurate, it is also very time consuming, requires elaborate equipment, and is very costly.

Bioelectrical impedance is another method of determining body composition. An electrode is placed on a toe and on a finger, and a small, painless electrical current is passed through the body. Muscle is over 75% water, therefore, it is a good conductor of electrical current. The more muscle that a person has, the faster the current will pass from the toe to the finger. Although bioelectrical impedance is a very popular method of body composition, it is not very accurate. If a person is dehydrated, perspiring, very obese, or very thin are all factors that could contribute to an error in calculating body composition by this method.

The most practical method of determining body composition is through skinfold measurements. With the skinfold technique, subcutaneous fat pinches are measured. Based on your age, a regression equation is formed that gives you a prediction of your current body fat. This method is very quick, very reliable, and does not require any expensive equipment.

Body composition assessment should be used to determine if a person is having success with hi or her exercise program. You should measure your body fat at the beginning of an exercise program and measure it again after a few months to see if you are making any progress. The average college age female is 25% body fat and the average female is 32%. The average college age male is 15% and the average male is 23% body fat.

Body Composition Classification According to Percent Body Fat
<19 12 12-17 17-25 25-35 35+
20-29 13 13-18 18-26 26-36 36+
30-39 14 14-19 19-27 27-37 37+
40-49 15 15-20 20-28 28-38 38+
50+ 16 16-21 21-29 29-39 39+
<19 18 18-22 22-30 30-40 40+
20-29 19 19-23 23-31 31-41 41+
30-39 20 20-24 24-32 32-42 42+
40-49 21 21-25 25-33 33-43 43+
50+ 22 22-26 26-34 34-44 44+


1. Determine how much of your body weight is fat weight (FW). To do this multiply your body weight (BW) by your percent body fat (%F).

2. Determine your lean body mass (LBM) by subtracting your fat weight from your body weight. (BW - FW = LBM)

3. Look up your ideal fat percentage (IFP) in the table.

4. Compute ideal body weight (IBW) according to the following formula: IBW = LBM ÷ (1.0 - IFP)

EXAMPLE: A 25 year old male weighs 200 pounds. He is 22% body fat.

1. Fat Weight (FW) = Body Weight (BW) x percentage of fat
FW = 200 x .22 (BF) = 44 pounds of fat

2. Lean Body Mass (LBM) = Body Weight (BW) - Fat Weight (FW)
Lean Body Mass (LBM) = 200 - 44 = 156 pounds of lean body mass

3. Ideal Fat Percentage (IFP) = 12% (.12 in decimal form)

4. Ideal Body Weight (IBW) = Lean Body Mass (LBM) ÷ (1.0 - Ideal Fat Percentage (IFP))

Ideal Body Weight (IBW) = 156 ÷ (1.0 - .12)
Ideal Body Weight (IBW) = 156 ÷ (.88)

Ideal Body Weight (IBW) = 177.27 pounds

If you have any questions regarding fitness and wellness, please feel free to contact me at (817) 648-6999.

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