Normal weights have been variously referred to as ‘ideal’, ‘desirable’ or ‘healthy’. Overweight refers to an increase on body weight above an arbitrary standard, usually defined in relation to height.
Quantification of adipose tissue mass can be achieved by a number of laboratory methods including underwater body density measurement and body fat content estimated by dual energy X-ray absorptiometer.
In addition, the development of new techniques, such as magnetic resonance imaging (MRI) and computed tomography (CT), has provided researchers with the opportunities to describe human adiposity in more detail.
However, most of these methods require costly equipment meaning that there is limited to clinical research setting.
The most widely used in Quetelet’s index, better known as body mass index (BMI), which is body weight (kg) divided by height squared (meter square). This index has been shown to correlate weakly with height and strongly with body fatness in adults. Because it is independent of age and reference population, BMI can be used for comparisons across studies both in the United States and internationally.
The World Health Organization classifies body fat by using BMI: Normal weight is a BMI of 17-24, overweight a BMI of 25-29 and obese a BMI of over 30.
This classification, even though based on large epidemiologic studies, gives a good estimate of the relation between body mass and disease.
Determining the weight status and level of adiposity in children and adolescent is even more problematical. This is a stage of rapid growth and development.
During growth in childhood and adolescence, not only does height increase but body composition changes as well, thus classification of obesity according to a single measure is difficult.
Definition of obesity and overweight
