How is obesity defined?
BODY MASS INDEX
Overweight and obesity are measured and determined using the body
mass index, or BMI. This is a simple, easy to apply, index of
weight-for-height that is commonly used to classify underweight,
overweight and obesity in adults. It is defined as the weight in
kilograms divided by the square of the height in metres (kg/m2).
BMI = weight (kg) / height (m) x height (m)
The classification of overweight and obesity, according to BMI,
is shown in the table below. This applies to men and women over
the age of 18 years.
Classification
BMI
Underweight Below
18.5
Normal
range 18.5
- 24.9
Overweight 25.0
- 29.9
Obese 30
or above
Therefore, a person is considered overweight when his or her BMI
is between 25.0 and 29.9, and obese when his or her BMI is
greater than or equal to 30.
NOTE:
-
As BMI is calculated using height and weight only, it therefore
does not measure body fat, and cannot differentiate between
weight that represents muscle and weight that represents
fat. This means that people who have the same BMI can
have a different percent body fat.
-
The limits defined above cannot be used to classify
underweight, overweight and obesity in children; different BMI
cut-offs are required. As BMI changes substantially with age in
children, BMI needs to be assessed using BMI-for-age charts,
where the child's BMI is plotted against their
age.
WAIST CIRCUMFERENCE
Waist circumference is another widely used measurement to
determine overweight and obesity, especially in the abdominal or
waist area.
Males
Females (aged >18
y)
Overweight > 94
cm > 80 cm
Obese >
102 cm > 88 cm
Waist circumference is a good indicator of increased risk of
developing health- and obesity-related problems and diseases,
particularly type 2 diabetes and heart disease. Therefore, waist
circumference is not only a measure of overweight and obesity,
but also an indicator of potential risk of other health problems.
Last updated 21st Feb 2005, by System Administrator