Body mass index (BMI) is a simple index of weight for height that is commonly used to classify underweight, overweight, and obesity in adults. It is the ratio of a person's body mass to the square of his or her height, expressed universally in kilograms per meter squared (kg/m2). BMI provides the most useful population-level measure of overweight and obesity, as it is the same for both sexes and for all ages of adults. However, BMI may not correspond to the same degree of fatness or associated health risk for some populations or individuals.
In Singapore, healthcare professionals frequently use BMI to check for weight categories that could cause health issues. The Health Promotion Board (HPB) has developed BMI reference standards and cut-off points for Singaporeans based on local studies. This article aims to provide an in-depth overview of BMI and its use in Singapore, including how to calculate BMI using the BMI calculator, the BMI classifications and cut-off points for Singaporeans established by HPB, as well as the various health risks associated with underweight, overweight, and obesity conditions based on recent research.
The concept of BMI was developed in the early 19th century by a Belgian statistician and sociologist named Adolphe Quetelet. He found a correlation between weight and height through statistical analysis of data collected from the military and believed that the relationship could provide a useful measure for populations. However, it was not until the 1970s that BMI was widely adopted as a simple screening tool for obesity by the Metropolitan Life Insurance Company in the United States.
In 1985, BMI was recommended by an expert committee convened by the World Health Organization (WHO) as a convenient and universal health indicator to classify underweight, overweight and obesity in adults. The WHO defined standard BMI categories and cut-off points that were adopted internationally. However, studies have since shown that the WHO BMI criteria may not be applicable to all ethnic populations. This led to the development of revised BMI standards tailored for Asian populations.
In Singapore, extensive population studies were conducted in the 1990s and 2000s involving tens of thousands of Singaporeans. This provided data on the relationship between BMI, percentage body fat and health risk factors in the local population. Based on these studies, HPB established BMI reference standards and cut-off points specifically for Singapore adults which differ slightly from international WHO criteria. HPB's BMI classifications have since been widely adopted in Singapore's healthcare system and by researchers.
To calculate BMI, you need two basic pieces of information - your weight in kilograms and your height in meters. Itmakes the calculation easy by just inputting your weight and height values.
There are several online calculators available that can calculate your BMI for Singapore. Some commonly used ones include:
- HPB BMI Calculator: Developed by the Health Promotion Board of Singapore based on local population studies. It is the most accurate calculator for Singaporeans as it uses the BMI cut-off points established for our population. The calculator can be accessed through the HPB website at www.hpb.gov.sg.
- National Health Service (UK) BMI Calculator: A simple one developed by the UK NHS that converts your weight in kg and height in cm/m to a BMI score. While not tailored for Singaporeans, it provides an easy way to calculate BMI on most devices. The calculator can be found at www.nhs.uk/bmi.
- BMI Calculator Apps: There are also several free mobile apps available on iOS and Android platforms that allow convenient calculation of BMI using your smartphone or tablet. Popular ones include BMI Calculator by PBC and BMI Calculator by Technogym.
To use any of these calculators, follow these simple steps:
1. Measure your height in meters without shoes on a stadiometer. For most accurate results, stand upright with your back against the height rod, heels together and touching the back upright portion of the stadiometer. If you know your height in centimeters, divide it by 100 to convert to meters.
2. Weigh yourself in light indoor clothing without shoes on a calibrated digital or medical scale. Make sure the scale is placed on a hard, flat surface.
3. Key in your height in meters rounded to one decimal place and weight in kilograms into the selected calculator.
4. The calculator will automatically calculate your BMI score based on the formula: BMI = Weight (kg) / [Height (m)]2
5. Take note of your BMI score and check your BMI classification based on HPB's standards for Singapore adults.
Based on extensive population studies involving over 50,000 Singaporeans aged 18 to 79 years old from 1992 to 2004, HPB has developed BMI reference standards and cut-off points that are more applicable for our local population.
The BMI classifications and cut-off points established by HPB for Singapore adults are:
- Underweight: BMI below 18.5 kg/m2
- Normal weight: BMI 18.5 to <23 kg/m2
- Pre-obese: BMI 23 to <27.5 kg/m2
- Obese Class I: BMI 27.5 to <32.5 kg/m2
- Obese Class II: BMI 32.5 to <37.5 kg/m2
- Obese Class III: BMI 37.5 kg/m2 or higher
Some key differences from WHO classifications:
- Pre-obese category introduced between normal and obese based on health risk assessment from local data
- Lower cut-off for obese class 1 at 27.5 kg/m2 instead of 30 kg/m2 based on findings of increased health risks above 27.5 kg/m2 for Asians
It is important to use the BMI classifications developed for Singaporeans by HPB for accurate interpretation of your BMI score and health risk level. However, BMI alone may not be able to distinguish between fat mass and fat-free mass components.
Maintaining a healthy weight through BMI screening helps reduce the risk of obesity-related diseases. Here is a more in-depth look at potential health issues associated with underweight, overweight and obesity conditions:
Underweight (BMI below 18.5 kg/m2)
Being underweight puts one at risk of nutritional deficiencies if dietary needs are not met. This can weaken the immune system and lower resistance to infections. Underweight individuals also have a higher risk of developing osteoporosis due to insufficient calcium and vitamin D intake over time.
For women, being underweight may disrupt the menstrual cycle and lead to irregular periods or amenorrhea. This poses fertility problems. Studies have found that being underweight before conception is linked to lower chances of maintaining a pregnancy. Underweight status in young women has also been associated with delayed sexual maturation and growth.
Pre-obese (BMI 23 to below 27.5 kg/m2)
The pre-obese category refers to being overweight but not yet obese. Individuals with a BMI in this range have a small increased risk of cardiovascular diseases like heart attacks and strokes compared to those with a normal BMI. They also face higher odds of developing type 2 diabetes mellitus.
If weight gain continues into the obese categories over time, the risks become much more significant. Therefore, those who are pre-obese should make efforts to prevent further weight increase through healthy lifestyle changes.
Obese (BMI 27.5 kg/m2 and above)
Being obese substantially raises the risk for serious medical conditions and reduced life expectancy. It is a major independent risk factor for cardiovascular diseases which remain the top cause of death in Singapore. Obese individuals have higher risks of developing coronary heart disease, heart attacks and strokes.
Obesity dramatically increases the likelihood of developing type 2 diabetes mellitus. The risk is about 50% higher for those with a BMI of 27.5 kg/m2 and more than doubles for a BMI over 32.5 kg/m2. Excess weight also puts immense strain on the body and raises blood pressure and cholesterol levels over time.
Other obesity-related health issues include non-alcoholic fatty liver disease (NAFLD), gallbladder disease, respiratory problems like sleep apnea, osteoarthritis and back pain. Carrying excess fat around the waistline in particular is linked to higher disease risks.
Being obese has also been identified as a risk factor for certain cancers. This includes increased risks of breast cancer in postmenopausal women, colon and rectal cancer as well as prostate cancer.
Studies have found that obesity can reduce life expectancy by an average of 3 to 10 years. It is estimated that being obese at 40 years old reduces the lifespan by 1 to 4 years on average. The health risks also rise progressively with increasing severity of obesity.
In summary, BMI is a simple yet useful screening tool to monitor weight status and potential health risks. By using the BMI calculator and understanding HPB's BMI classifications, Singaporeans can keep track of their weight trends over time. Together with other health indicators, regular BMI screening through lifestyle modifications helps prevent obesity and related diseases from developing. Maintaining a healthy BMI, diet and activity levels is important for overall well-being and longevity.