Understanding Your BMI: What Is It and What It Means
Takeaways
Your weight cannot offer you the whole picture of your health—that bit is true.
However, that doesn't mean you shouldn't care about the numbers on the scale. Your weight can still serve as a straightforward, inexpensive way of determining your risk for developing various chronic diseases, like type 2 diabetes.
So, how would you know if you're at a "healthy" weight? Well, that's where the Body Mass Index (BMI) comes into play.
In this article, we cover what BMI is, how you can calculate your BMI, its limitations, and various weight loss tips—so you understand what it'll take for you to reach a "healthy" weight.
What is BMI?
Body mass index (BMI) is a crude estimate of one’s body fat based on one’s height and weight. It’s typically used as an inexpensive screening method for weight categories: ”underweight”, “healthy weight”, “overweight”, or “obesity”.
Dividing your weight (in kilograms) over your height, squared, in metres will give you your BMI value.
Here’s the formula:
BMI = weight (kg) / height (m) 2
Now, let’s work through an example together. Assume that the following are your statistics:
Weight: 60 kg
Height: 1.65 m
Your BMI would thus be 22.0 kg/m2 (60 kg / 1.65 m2).
Interpreting BMI values
For adults, the World Health Organization (WHO) defines the BMI cut-offs for overweight and obesity as follows:
Overweight: BMI greater than or equal to 25
Obesity: BMI greater than or equal to 30
That said, it doesn’t necessarily mean that you’re within the healthy weight range if your BMI value falls below 25 kg/m2. Why? Well, that’s because these BMI cut-off points are derived from studies on the relationship between BMI, morbidity, and mortality in the Western populations.
In other words: they’re not generalizable to the Asian population, who’s known to have a higher prevalence of type 2 diabetes and increased cardiovascular risk factors at lower BMI values than the Western population.
To that end, the WHO established an expert consultation in 2004 to address the appropriate BMI classification for Asian populations—and recommended adding cut-off points of 23, 27.5, and 37.5 kg/m2 as points for public health actions.
In Singapore, specifically, the current Ministry of Health (MOH) Clinical Practice Guidelines’ classification for overweight and obesity is as follows:
Overweight: BMI greater than or equal to 23
Obesity: BMI greater than or equal to 27.5
| Cardiovascular disease risk | Asian BMI cut - off points | WHO BMI cut - off points |
|---|---|---|
| Low | 18.5 - 22.9 | 18.5 - 24.9 |
| Moderate | 23.0 - 27.4 | 25.0 - 29.9 |
| High | 27.5 - 32.4 | 30.0 - 34.9 |
| Very High | 32.5 - 37.4 | 35.0 - 39.9 |
Bottom line? A BMI value between 18.5 to 23 kg/m2 is ideal if you’re of Asian ethnicity, while a BMI value between 18.5 to 25 kg/m2 is ideal if you’re non-Asian.
Why is a high BMI bad?
As briefly mentioned earlier, your BMI is an estimate of your body fat. It’s a good gauge of your risk for various chronic diseases, including heart disease, high blood pressure, type 2 diabetes, and certain cancers.
Research also shows a link between increased BMIs and a higher risk of diabetes complications among people with diabetes.
Limitations of BMI
BMI is a useful estimation of one’s body fat. However, it fails to account for the following:
Fat distribution: Your body has 2 primary kinds of fat, subcutaneous (lies just beneath the skin) and visceral fat (lies deep within your abdominal walls and surrounds your organs). Generally speaking, visceral fat is more concerning than subcutaneous fat owing to its association with various health risks, including heart disease, type 2 diabetes, and some types of cancer. Thus, an individual with, say, 30 kg of subcutaneous fat would technically be healthier than another who has 30 kg of visceral fat—but, unfortunately, BMI fails to distinguish between the two types of fat.
Age or gender: A woman tends to have more body fat than a man with the same BMI. An older person tends to have more body fat (due to loss of lean muscle mass with aging) than a younger person with the same BMI.
In light of these limitations, several health experts have increasingly pushed for the measurement of an individual’s abdominal obesity—via waist circumference—as an indicator of their body fat distribution (in addition to BMI value), and, hence, health risk.
The International Diabetes Federation’s definition of the metabolic syndrome defines abdominal obesity for the Asian population is as follows:
Asian women: A waist circumference of above 80 cm
Asian men: A waist circumference of above 90 cm
Benefits of weight loss
If you have a high BMI and carry excess fat around the abdominal area, losing weight could protect your health in many ways. Even moderate weight loss of 5-10% of body weight can result in health benefits, such as improved blood pressure, blood sugar, and blood cholesterol.
Studies have shown that people with a high risk of developing type 2 diabetes can prevent or delay the onset of diabetes by losing a modest amount of weight through lifestyle changes (dietary changes and increased physical activity).
For people with type 2 diabetes, weight loss has been shown to improve sugar control and can even help to bring type 2 diabetes into remission. It could also reduce the risk of cardiovascular diseases.
How can I lose weight?
Many of us eat and drink more than we realize. Unfortunately, we also often don’t get enough physical activity. Calorie input that exceeds calorie output will result in fat accumulation and weight gain.
The key to losing weight lies in burning more calories than you consume daily. Here are a few tips that’ll help you do so:
Choose healthier dietary options: Make the most of your calories by choosing nutrient-dense foods and reducing your intake of refined carbohydrates and saturated fats.
Watch your portion sizes: It’s important to be aware of portion sizes when we eat, as it’s easy to over-indulge, especially for things we love!
Start moving more: Aim to do moderate-intensity activity regularly, for at least 150 minutes per week. This will go a long way to helping you lose weight.
A healthy weight loss target would be about 0.5 kg to 1 kg per week. What’s important is to start with small, realistic changes that you could progressively build up over time to ensure that your new healthier lifestyle is sustainable over the longer term.
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