Understanding Body Mass Index (BMI): What I Commonly Explain to My Patients
In my daily practice, one of the most common measurements patients ask about is Body Mass Index, or BMI. Many people see their BMI number on a health screening report and immediately feel worried or confused. I often explain that BMI is a simple screening tool — not a full picture of health, but a useful starting point.
What is Body Mass Index?
Body Mass Index is a calculation based on your weight and height:
BMI = weight (kg) ÷ height (m²)
It helps categorize a person into:
- Underweight
- Normal weight
- Overweight
- Obese
However, I always remind patients that BMI does not directly measure body fat or overall health.
Why BMI is Used in Medicine
From a clinical perspective, BMI is helpful because it:
- Provides a quick screening tool for population health
- Helps identify risk of conditions like diabetes, hypertension, and fatty liver disease
- Allows doctors to monitor weight trends over time
In Malaysia, we often see increasing cases of metabolic diseases linked to rising BMI levels, especially in urban lifestyles.
Limitations of BMI (What Patients Often Don’t Know)
One thing I frequently explain is that BMI has important limitations:
- It does not differentiate fat from muscle
- Athletes may have a high BMI but low body fat
- Older adults may have normal BMI but higher fat percentage
- It does not show fat distribution (belly fat is more risky)
So, BMI alone should never be used to judge health status.
When BMI Becomes a Health Concern
In my consultations, I become more attentive when BMI is associated with other risk factors such as:
- High blood pressure
- Elevated blood sugar
- High cholesterol
- Fatigue or reduced physical activity
- Central obesity (abdominal fat)
In these cases, BMI becomes part of a bigger health picture rather than a standalone number.
When to See a Doctor
You should consider medical evaluation if:
- Your BMI is consistently in the overweight or obese range
- You are gaining weight rapidly without clear reason
- You have symptoms like breathlessness, fatigue, or snoring
- You have a family history of diabetes or heart disease
Early assessment allows us to prevent long-term complications.
Doctor's Insight
In my experience, BMI is best used as a starting point, not a final judgment. I often tell patients that health is not defined by a single number, but by a combination of lifestyle, metabolic health, and physical wellbeing.
If your BMI concerns you, it is always better to assess it early rather than ignore it.
– Dr. Teh Boon Teong
Consultant in Internal Medicine
Evercare Medical Care Centre, Penang, Malaysia.
Frequently Asked Questions
It is useful for screening but not fully accurate for individual health.
Generally 18.5–24.9, but this varies by ethnicity and health status.
Yes, especially if metabolic markers are normal.
No, it does not distinguish fat from muscle.