BMI has its uses, says health board

I refer to Dr Andy Ho's commentary, 'Checking BMI's a fat lot of good' (Oct 10, 2009).

The Health Promotion Board (HPB) agrees with Dr Ho that the Body Mass Index (BMI) does not distinguish between fat, lean mass nor fat distribution.

Although BMI does not measure body fat directly, research has shown that it correlates well with other more direct measures of body fat, such as underwater weighing and dual energy X-ray absorptiometry (Dexa).

BMI is, therefore, considered an alternative measure of body fat. Measuring BMI is an inexpensive, simple and reasonably accurate method of screening for weight categories that may lead to health problems.

In 1995, the World Health Organisation recommended using BMI cut-off points of 25 kg/m2 and 30 kg/m2 to identify overweight and obese individuals, respectively. Subsequent studies showed that Asians have 3 to 5 per cent more body fat and a higher risk of developing heart disease, compared to Caucasians of the same gender and age with the same BMI.

It was recommended that for Asians, a BMI of 23 kg/m2 or higher indicates a moderate increase in risk while a BMI of 27.5 kg/m2 or higher represents a high risk of developing these conditions.

These are cut-offs that HPB uses in our public education messages. We believe this further addresses issues of accuracy and is useful for individuals as a start point to manage their weight and risk.

As highlighted, BMI measurement is not an accurate predictor of risk for those who are muscular. The risk of developing cardiovascular disease is also dependent on levels of blood lipids, diabetes or hypertension.

Hence, public education on obesity does not focus on BMI alone but also recommends regular screening for those over 40 for early detection and optimal management of high blood pressure, high blood cholesterol and diabetes.

BMI, in combination with blood pressure readings, lipid levels and blood glucose levels, provides a far better assessment of risk, compared to BMI on its own, or total body fat measurement (for example, using the Bod Pod) on its own.

We thank Dr Ho for his absorbing commentary and the opportunity to discuss the use of BMI as a tool for measuring health risks. We invite the public to visit our website at www.hpb.gov.sg for more information.

Dr Shyamala Thilagaratnam
Director, Healthy Ageing Division
Health Promotion Board

Source: The Forum of the Straits Times dated 31 October 2009.