Citing the 2019 national health and morbidity survey, it said 50.1% of the adult population was either overweight (30.4%) or obese (19.7%).
BMI checks have been a standard health screening tool to determine the “ideal” weight of a male and female adult. However, is the BMI the be-all and end-all as an indicator of health?
What is BMI?
BMI (kg/m2) is an indirect measure of the amount of body fat and is determined by dividing the weight (kg) of a person by the square of height (m).
The general adult cut-offs for BMI for both sexes are:
- Underweight: <18.5
- Normal: 18.5 to 24.9
- Overweight: 25.0 – 29.9
- Obese: ≥30.0
The president of the Nutrition Society of Malaysia (NSM), Tee E Siong, said BMI was particularly useful as a public health measure to classify individuals as underweight, overweight and obese.
“It is a simple, inexpensive and non-invasive measure of body fat for population groups,” he said.
History
The formula, first known as the Quetelet Index, was proposed by a Belgian mathematician, Adolphe Quetelet, to statistically define the characteristics of the “ideal man” based on data collected from French and Scottish men. It was renamed the BMI in 1972 by Ancel Keys, an American physiologist.
“The Malaysian healthcare system adopted it in the 1990s and it appeared in the first official Malaysian Dietary Guidelines in 1999,” said Tee.
Since 2008, BMI checks have been part of the mandatory national physical standard test (SEGAK) to measure fitness levels of students aged 10 to 17.
How does it work in adults and children?
The way to calculate BMI for children is the same as that for adults. However, the classification for underweight, overweight and obese among children differs from that of adults.
Nutritionist Yasmin Ooi of University Malaysia Sabah said that in different Asian populations, the cut-off point varied from 22 to 25 kg/m2.
“This is because Asians have higher total body fat for the same BMI compared with white Europeans and, therefore, higher risks of non-communicable diseases such as Type 2 diabetes and cardiovascular diseases. In Malaysia, a BMI cut-off point of 23.0 and higher indicates overweight,” she said.
Tee said in children and adolescents, the amount of fat varied even more among genders and age groups.
“The World Health Organization recommends using BMI-for-age tables for children five to 19 years of age and different tables are used for boys and girls,” he said.
Limitations of using BMI
Based on the formula, BMI actually measures weight rather than fat and is not a true measure of the amount of fat in the body or where the fat is distributed.
Body fat distribution varies between men and women. Men tend to accumulate fat in the abdomen while women tend to accumulate fat in the gluteal-femoral region (buttocks).
Tee highlighted several factors like age, sex, ethnicity and muscle mass that affect the relationship between BMI and body fat.
“For instance, older adults and women tend to have more body fat than younger adults and men respectively. Also, athletes may have a higher BMI compared with an average person because they have more muscle mass,” he said.
Ooi said that when managing health risks on an individual basis, BMI should not be used as the sole indicator of health.
“Other indicators of health also need to be looked at, including abdominal obesity, total body fat, and considerations need to be made for those with short stature or unusually high muscle mass,” she said.
However, in public health, BMI is a convenient method to flag up the need for interventions to reduce overweight and obesity in the population.
For children, BMI-for-age can act as an early marker of childhood obesity and draw the correct attention to the prevailing problem.