BMI Cannot Be Used Alone to Measure Health

Body mass index, or BMI, is a tool doctors use to check how much a person weighs compared to how tall they are. The calculated number is often used as a screening tool. Having too much body fat can cause problems. But so can having too little body fat.¹

BMI helps to categorize body sizes as:¹

• Underweight
• Optimal
• Overweight
• Obese

Debate over using BMI to measure health

BMI is a simple way for doctors to check how much a person weighs. But it does not always tell the whole story. There are other issues with using BMI alone to determine health. Looking at these drawbacks is important to understand the whole picture.²

Critics of BMI point out that it does not account for factors such as:²

• Muscle mass
• Body composition
• Location of fat on the body

All of these factors can vary widely from person to person.¹

BMI limitations

One problem is that BMI does not factor in things like muscles or bones. So people who have more muscle, like athletes, might have a high BMI even if they are not overweight.¹

BMI cannot tell the difference between different kinds of body fat, like fat around organs or under the skin. But some fat is worse for you and can cause health problems. BMI does not show where the fat is, so it cannot help with that.¹

Research has shown that fat stored around the organs is linked to an increased risk of various health problems, like:¹

• Disease of the heart and blood vessels
• Type 2 diabetes
• Metabolic syndrome
• High blood pressure
• Gallstones

But BMI alone cannot provide information about the distribution of body fat.¹

BMI may not equally apply to all people. This can lead to ineffective screening for health problems, especially among people of color. The BMI categories may not accurately reflect health risks for people who are not white. This may result in underdiagnosis or misdiagnosis of obesity-related health conditions.³

BMI is not enough to give a complete picture of someone's health. It does not take into account other important factors like:^1,3

• Waist size
• Body fat percentage
• Underlying medical conditions

While BMI is a helpful tool, doctors need to consider other factors to get a more accurate understanding of a person's overall health.³

Beyond BMI

Knowing BMI’s limits, doctors are working on other ways to check weight and body shape. One way is measuring the waist. This is looking at how big the waist is around the belly button. It can show if there is too much fat around the organs, which can be bad for health.^2,4

In 2023, doctors and policy makers of the American Medical Association (AMA) reported that BMI does not tell the whole story about a person’s health. Instead, the AMA now recognizes overweight and obesity as complex issues. And that different approaches are needed depending on the person’s:⁴

• Medical history
• Sex and gender
• Race and ethnicity
• Age
• Lifestyle

Understanding optimal health and well-being includes looking at all parts of a person’s health, not just BMI.⁴