BMI: Why it’s not the best measure of your health

If you’ve ever stepped on a scale and calculated your Body Mass Index (BMI), you might have wondered: does this number really tell me if I’m healthy?

The truth is: while BMI is a widely used tool, it’s far from perfect.

Here’s why you shouldn’t rely on it alone to determine whether you’re at a healthy weight.

What Is BMI?

BMI (Body Mass Index) is a simple calculation based on your weight and height:

BMI = weight (kg) / height² (m)

According to general guidelines:

A BMI below 18.5 is considered underweight
18.5–24.9 is the "normal" range
25–29.9 is classified as overweight
30+ is considered obese

The flaws of BMI

1. It doesn’t account for muscle vs. fat

BMI treats all weight the same, whether it’s muscle, fat, or bone. A bodybuilder with low body fat could easily be classified as "overweight" or even "obese" because muscle is denser than fat. Meanwhile, someone with a "normal" BMI could still have high body fat and poor metabolic health.

2. It ignores fat distribution

Two people with the same BMI could have completely different health risks: one might carry fat around their organs (visceral fat, high risk for diabetes and heart disease), while the other stores it in their hips or thighs (subcutaneous fat, under the skin, lower risk).

3. It doesn’t consider age, sex, or bone structure

Women naturally have more body fat than men, yet BMI categories don’t fully adjust for this.
Older adults tend to lose muscle mass, which can make BMI misleading.
A person with a larger frame might weigh more without being unhealthy.

What should you use instead?

Since BMI has limitations, consider these better indicators of health:

Body fat percentage (via DEXA scan, calipers, or bioelectrical impedance)
Waist-to-hip ratio (a better predictor of heart disease risk)
Blood markers (cholesterol, blood sugar, inflammation levels)
Strength and fitness level (can you perform daily activities without fatigue?)

The Bottom Line

BMI is a quick, easy screening tool, but it’s not the final word on your health. If you’ve been frustrated by a high BMI despite being fit, or if your BMI is "normal" but you feel sluggish, dig deeper. True health is about how you feel, how you move, and how your body functions, not just a number on a chart!

Sources:

Yale Medicine, Why you shouldn't rely on BMI alone
Harvard T.H. Chan School of Public Health - BMI: a poor metric for measuring people's health
National Center for Biotechnology Information (NCBI) - Age, sex, and bone structure in BMI
University of Rochester Medical Center (URMC) - Is BMI accurate?
University Hospitals - Should we stop using BMI to measure health?
Within Health - Why body weight Isn’t an indicator of health