Body Mass Index (BMI) is the most widely used screening tool for assessing weight relative to height. It is quick, free, and requires nothing more than a scale and a measuring tape. But it has real limitations that are particularly relevant for South Asian populations including Bangladeshis — and understanding those limitations is just as important as knowing your number.
How BMI Is Calculated
The formula is straightforward: BMI equals your weight in kilograms divided by your height in metres squared.
BMI = Weight (kg) / Height² (m²) Example: Weight 70 kg, Height 1.68 m BMI = 70 / (1.68 × 1.68) = 70 / 2.8224 = 24.8
Standard WHO BMI Categories
The World Health Organisation defines BMI categories as follows for adults.
WHO BMI Classification
| BMI Range | Classification |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese (Class I and above) |
Why Standard Thresholds May Not Apply to Bangladeshis
Multiple studies have found that South Asian populations — including Bangladeshis — develop metabolic risk factors like type 2 diabetes, hypertension, and cardiovascular disease at lower BMI values than Western populations. The WHO itself, and the World Health Organisation Expert Consultation on BMI in Asian Populations, recommended lower action thresholds for Asian-Pacific groups.
WHO Recommended Thresholds for Asian-Pacific Populations
| BMI Range | Classification |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 22.9 | Normal weight |
| 23.0 – 27.4 | Overweight (increased risk) |
| 27.5 and above | Obese (high risk) |
This means a Bangladeshi adult with a BMI of 24 — well within the 'normal' range on the standard WHO scale — may actually be in the 'overweight' category on the Asian-Pacific scale. Many health organisations in Bangladesh and the broader South Asian region have adopted these lower thresholds for clinical screening.
The Real Limitations of BMI
BMI does not distinguish between fat mass and muscle mass. A physically active person with significant muscle will have a higher BMI than someone of the same height and body fat percentage who is sedentary — and yet the active person has lower metabolic risk. BMI also does not capture where body fat is distributed, which matters significantly: abdominal fat (central obesity) carries far higher health risk than fat stored around the hips and thighs.
A More Useful Measurement: Waist Circumference
For South Asian populations, waist circumference is often a better predictor of metabolic risk than BMI alone. The International Diabetes Federation and multiple South Asian guidelines suggest that for South Asians, abdominal obesity is defined as a waist circumference of 90 cm or more for men, and 80 cm or more for women.
Tip
Use BMI as a screening indicator, not a diagnosis. If your BMI flags a concern, the more useful next steps are: measure your waist circumference, have a fasting glucose and lipid panel done, and discuss the findings with a doctor who can look at the full picture rather than a single number.