BMI should be replaced: here's why and what with

The body mass index (BMI) is often used to assess health risks, but a recent study questions its reliability. Researchers suggest that body fat percentage would be a more accurate indicator.

The study, published in the Annals of Family Medicine, reveals that BMI does not accurately predict mortality risk. In contrast, body fat percentage shows a clear correlation with this risk. This finding could lead to a revision of the prescription criteria for obesity medications.


Experts point out that BMI, although simple to calculate, has significant limitations. It does not distinguish between muscle mass and fat, nor does it account for the distribution of fat in the body. These shortcomings can lead to misclassification of patients.

The bioelectrical impedance analysis (BIA) method offers a more accurate alternative. It measures tissue resistance to an electrical current to estimate body composition. However, this technique is not without flaws, particularly regarding fat localization.

The implications of this study are significant for medical practice. The authors call for a revision of practices to include body fat percentage in prescription criteria. This would better identify at-risk patients, even those with a normal BMI.

What is bioelectrical impedance analysis?

Bioelectrical impedance analysis (BIA) is a method that measures body composition by sending a weak electrical current through the body. This current encounters different resistances depending on the tissues, allowing for an estimation of fat and lean mass.

BIA is based on the principle that muscle tissues, rich in water, conduct electricity better than fatty tissues. This difference helps distinguish tissue types and calculate their proportion in the body.

Although BIA is more accurate than BMI, it has limitations. The localization of fat, particularly around organs, is not always well captured. Additionally, hydration and other factors can influence the results.

Despite these limitations, BIA is increasingly used in clinical settings and even at home thanks to smart scales. Its accessibility and relative simplicity make it a promising tool for assessing health risks.

Why is BMI an imperfect indicator?

BMI is calculated from weight and height, without distinguishing between fat mass and muscle mass. This can lead to misclassifications, such as athletes with significant muscle mass being considered overweight.

Moreover, BMI does not account for fat distribution in the body. However, visceral fat, located around organs, is more dangerous to health than subcutaneous fat. BMI may therefore underestimate the risk in some individuals.

BMI categories were primarily established based on white Caucasian populations, limiting their applicability to other ethnic groups. This can lead to disparities in health risk assessments.

Finally, BMI does not provide information on individual metabolic risk factors. Two people with the same BMI can have very different health profiles, depending on their body composition and lifestyle.