While the numbers span a broad range for what is a "normal" body fat percentage, most health authorities agree that for men 25 percent or more is obese, and for women the number is 35 percent.
Underwater weighing
This method measures the density of your body relative to the density of water. Fat floats, so the lighter you are in water, the more body fat you have. While this technique is considered very reliable, inaccuracies arise if the equipment is not well calibrated. In addition, if you are unable to exhale all the air from your lungs during the measurement, you become more buoyant and erroneously register more body fat.
Skinfold measurements
Skinfold calipers, resembling ice tongs, measure thickness of subcutaneous (under the skin) body fat. Skin is folded (pinched) at specific body sites - triceps, thigh, hip, and subscapular skin folds. The thicknesses of all skin folds are converted into body fat percentages, using one equation designed for men and another for women. This method can be accurate if a skilled technician is taking the fold measurements.
Inaccurate results are commonly caused by rushed, sloppy measurement; also, you may have unusual body fat distribution, with more or less than normal fat stored at the traditional measuring sites.
Bioelectrical impedance
This computerized method can be done quickly, without getting wet or holding still for skinfold measurements. The body fat measurement comes from determining the resistance your body gives to an electrical current sent through body tissues from electrodes attached to your wrists and ankles. Water, found primarily in nonfat tissue, has little resistance to the electrical current. On the other hand, fat tissue provides greater resistance; thus, the more body fat you have the more resistance to the electrical current.
This method of body fat determination is accurate provided you haven't done anything to offset your normal water balance. Abnormal water balance can occur after a long workout, after consumption of alcoholic beverages or coffee, or even after taking certain medications. This method does seem to overestimate body fat for excessively overweight people, and this technique is not appropriate for the elderly.
Infrared interactance
This technique, originally used for meat grading by the U.S. Department of Agriculture, is based on the absorption of near-infrared light. A wand, connected to the computer, shines light directed to a specific site on the body. The computer calculates body fat by the way this light scatters and how much is absorbed. This method has been strongly criticized, since whole body fat is being calculated from information determined at just one site on the body.
Body Measurements
This is a rapid, easy method to determine your lean body mass, using a tape measure and height scale. This is a relatively untested method and little has been done to test it's reliability. Still, if you use this method to determine a "base" point and repeat with the same method over time, changes can be measured, though the actual percentage of body fat may not be totally accurate.
Note:BMI has nothing to do with percent body fat. Don't confuse the two! BMI is just an index - a number - computed from height and weight; it fails to take into account percent body fat.
Go to BMI Index Calculator to determine your BMI.
A BMI from 20 through 24.9-desirable for most middle-aged adults. (Nonsmokers with a consistent BMI within this range have the lowest risk of disease and premature death.) In this category, weight gain can be avoided through moderate eating habits and exercise.
A BMI from 25 through 29.9-moderately overweight-carries a slightly increased risk of weight-related health problems, such as high blood pressure, high blood cholesterol, heart disease and adult-onset diabetes. People in this group have the hardest decision to make about reducing, given the potential health risks of weight loss. To prevent the development of weight-related health problems, most people in this category should avoid gaining additional pounds by adopting a low-fat diet and a routine of regular exercise. Weight loss for cosmetic reasons is very common here.
At a BMI of 30 or more-obese-the risk of developing heart disease and other weight-related conditions rises sharply. Most people should lose weight in this category. Adult-onset diabetics in this category should definitely reduce, since blood-sugar control improves with weight loss.
At a BMI of 40 or more-severely overweight-you are in great danger of dying early. 80% eat
in frequent binges. Secret eating is common. Best weight loss technique is often surgery. With
the addition of new medicines for weight control, and more coming, the morbidly obese may
be able to avoid surgery. This is still not clear. Benefits of losing weight clearly outstrip any
dangers. A trial of medicines should always be done before going to surgery.
Check this site: BMI risk levels for a more detailed listing of BMI ratings.