BMI: How Much Does It Really Say About Your Health?

What's the importance of the BMI?

Many people visit their doctor, have their weight and height measured, and walk away with a number called their BMI—body mass index. But without context, that number can leave someone with either a false sense of security or unnecessary alarm.

What Is BMI?

BMI is calculated by dividing your weight in kilograms by your height in meters squared. It’s a simple formula, and it’s widely used to sort people into weight categories:

• Underweight: Below 18.5 kg/m²

• Normal weight: 18.5–24.9 kg/m²

• Overweight: 25–29.9 kg/m²

• Obese: 30 kg/m² or higher

The Problem with BMI

The American Medical Association (AMA) recommends that BMI should never be used by itself to guide weight-loss recommendations or assess cardiovascular risk. Why?Because BMI doesn’t tell the whole story.

BMI treats all weight the same—whether it comes from muscle, fat, or bone. A short, muscular person could appear “overweight,” while a tall person carrying excess body fat might still land in the “normal” range.

Why Fat Location Matters

Where fat is stored can be even more important than how much you have. Visceral fat, which collects around the abdomen and organs, is strongly linked to:

• Insulin resistance

• Metabolic syndrome

• Type 2 diabetes

• Heart disease

• High blood pressure

Two people with the same BMI can have very different risks depending on whether their fat is concentrated in the waist or lower body.

The Hidden Risk: Fat in the Liver

In people with a normal BMI, fat stored in the liver—known as non-alcoholic fatty liver disease (NAFLD)—can be an even stronger predictor of heart disease risk. BMI cannot detect this.

Better Measures for Your Health

While BMI is a useful screening tool for population health studies, your doctor may use additional tests for a clearer picture:

• Waist circumference and waist-to-hip ratio

• Body fat percentage using skinfold measurements, bioelectrical impedance, or DEXA scans

The Bottom Line

BMI can be a starting point, but it’s not the final word on your health. Pair it with other measurements—and professional guidance—for the most accurate assessment of your risk factors.