How do you know if you are overweight’? Being heavy does not necessarily mean you are unhealthy. Bodybuilders and rugby players, for example, are heavy but they are definitely not unhealthy. Their “excessive” weight is the result of increased muscle mass and muscle is good tissue.

Our bodies are made up mainly of bone, muscle and fat. It is excessive fat, rather than bone or muscle, that contributes to what is considered an unhealthy weight. It is body fat that we are interested in when determining whether our weight is healthy or unhealthy.

There are several techniques of measuring body fat: body mass index (BMI), waist circumference, waist-to-hip ratio, skinfold (caliper test), bioelectrical impedence analysis (BIA), DEXA, near-infrared (NIR) interactance, hydrostatic weighing and air displacement.

Of these, BMI and waist circumference are the two most useful methods and, in practice, they are all that is needed.

Body Mass Index

The body mass index (BMI) is a weight-to-height ratio. It is associated with the individual’s body fat percentage and the risk of co-morbidities, or related diseases, and is thus the recommended index for determining whether one is overweight or obese.

The BMI is calculated as follows:

MBI = Weight (in KG) / (Height (in m) x Height)

For example, a 1.65 m-tall person weighing 7 5 kg will have a BMI of 27.5 kg-nr2, calculated using the formula as follows: 75 – (1.65 x 1.65).

The higher the BMI, the greater the degree of fatness and the greater the risk of obesity-related diseases, such as hypertension, diabetes mellitus, hyperlipidemia and heart disease.

As fat levels increase, we see the risk of obesity-related conditions increase as the BMI increases. However, it is noteworthy that there are also health risks associated with a low BMI, albeit a different set of problems, such as osteoporosis, menstrual irregularities, heart problems and malnutrition.

Recent studies done in Indonesia, Singapore, Japan and Hong Kong show that, for the same BMI values, Asians have more body fat (and thus greater cardiovascular risk). The
BMI cut-off points for Asians have therefore been adjusted. Hence, while the ideal BMI range for Caucasians is 18.5 kg-m2 to 24.9 kg-m2, the optimal range for Asians is 18.5 kg-m2 to 22.9 kg-m2.

The BMI is only an estimate and has its limitations. It assumes a person with the “typical” proportion of fat, muscle and bone and does not take into account deviations from the norm, such as in muscular individuals, pregnant or lactating women, children or the elderly. For children, an age- and gender-specific BMI chart should be used.