HOW DO YOU
DECIDE IF YOU WEIGH TOO MUCH?
What is obesity?
needs a certain amount of body fat for stored energy, heat insulation, shock absorption, and other
functions. As a rule, women have more fat than men. Doctors generally agree that men with more than
25 percent body fat and women with more than 30 percent body fat are obese. Precisely measuring a
person's body fat, however, is not easy. The most accurate method is to weigh a person underwater --
a procedure limited to laboratories with sophisticated equipment.
There are two simpler methods for estimating body
fat, but they can yield inaccurate results if done by an inexperienced person or if done on someone
with severe obesity. One is to measure skin fold thickness in several parts of the body. The second
involves sending a harmless amount of electric current through a person's body (bioelectric
impedance analysis). Both methods are commonly used in health clubs and in commercial weight-loss
programs, but results should be viewed skeptically.
Because measuring a person's body fat is tricky,
doctors often rely on other means to diagnose obesity. Two widely used measurements are
weight-for-height tables and body mass index. While both measurements have their limitations, they
are reliable indicators that someone may have a weight problem. They are easy to calculate and
require no special equipment.
Most people are familiar with weight-for-height tables. Doctors have used these tables for
decades to determine whether a person is overweight. The tables usually have a range of acceptable
weights for a person of a given height.
One problem with using weight-for-height tables is
that doctors disagree over which is the best table to use. Many versions are available, all with
different weight ranges. Some tables take a person's frame size, age, and sex into account; others
do not. A limitation of all weight-for-height tables is that they do not distinguish excess fat from
muscle. A very muscular person may appear obese, according to the tables, when he or she is not.
Still, weight-for-height tables can be used as general guidelines.
Body mass index (BMI)
Body mass index, or BMI, is a new term to most people. However, it is the measurement of choice
for many physicians and researchers studying obesity. BMI uses a mathematical formula that takes
into account both a person's height and weight. BMI equals a person's weight in kilograms divided by
height in meters squared. (Or, weight in pounds divided by height in inches squared, and multiplied
by 704.5). You can figure out your BMI with our
While the BMI measurement poses some of the same
problems as the weight-for-height tables, it's a useful general guide.