July 05, 2025

Why BMI is a bad way to measure health and what might be better

You’ve probably heard of BMI, or Body Mass Index. It’s that number calculated from your height and weight that’s supposed to tell you if you’re underweight, normal, overweight, or obese. For decades, doctors, insurance companies, and fitness experts have leaned on BMI as a quick way to assess health. But here’s the truth: BMI is a pretty flawed tool, and relying on it can do more harm than good.

First off, BMI is just a simple calculation. It takes your weight in kilograms and divides it by your height in meters squared. That’s it. What it does not do is differentiate between fat, muscle, bone, or water weight. So, for example, a muscular athlete who weighs more because of muscle mass might be labeled “overweight” or “obese” by BMI standards, even though they have very low body fat and are in excellent health. On the flip side, someone with a “normal” BMI could have a high percentage of body fat and be at risk for heart disease or diabetes. This shows BMI’s major limitation: it doesn’t actually measure body composition.

Another problem is that BMI doesn’t consider where fat is distributed on your body. Fat around the belly is much more dangerous than fat around the hips or thighs because it is linked to higher risk of heart disease and metabolic issues. Two people with the same BMI can have very different health outcomes depending on their fat distribution. So, BMI is too broad and generalized to give an accurate picture of health risk.

BMI also doesn’t work well across all ethnicities or ages. Studies show that people from different ethnic backgrounds may have different body fat percentages at the same BMI. For instance, some Asian populations have higher health risks at lower BMIs, while some Black populations might be healthier at higher BMIs. Older adults may lose muscle and bone density but still have a “normal” BMI that hides their true health status. This lack of nuance makes BMI unreliable for many people.

Given all these flaws, what’s a better way to measure weight or health? One of the simplest alternatives is to look at body composition directly. Tools like bioelectrical impedance scales, DEXA scans, or skinfold calipers estimate the percentage of fat versus lean muscle in your body. This gives a much clearer picture of your health than just weight and height.

Measuring waist circumference is another easy way to gauge health risk. A larger waist size often signals more dangerous visceral fat around your organs, which is linked to increased risk of diabetes, heart disease, and stroke. It’s simple, inexpensive, and tells you more about your health than BMI alone.

Of course, no single number tells the whole story. Your overall lifestyle — including diet, physical activity, sleep, stress levels, and mental health — plays a huge role in your well-being. Instead of fixating on BMI, it’s better to focus on how you feel, your energy levels, and regular check-ups that include blood pressure, cholesterol, and blood sugar levels.

In short, BMI is a convenient but overly simplistic tool that can mislead people about their health. It does not distinguish muscle from fat, ignores fat distribution, and overlooks differences in age and ethnicity. Better options include measuring body fat directly, tracking waist circumference, and focusing on overall health habits. So next time someone asks for your BMI, remember that it’s just one piece of the puzzle, and not the best way to understand your body or health. Your worth and wellness are so much more than a number on a chart.