Why BMI Is Not the Best Measure of Health

Body mass index (BMI) has long been a standard in health evaluations, but researchers are questioning its efficacy. BMI, which factors in a person's weight and height, was designed to indicate excess fat and potential risks for obesity-related health issues. However, studies show that BMI alone misses diagnosing obesity in nearly 9% of people and incorrectly labels 3% as having obesity when their weight isn't an immediate health concern.

A new framework developed by researchers at King’s College London suggests that combining BMI with other measurements, such as waist circumference or waist-to-height ratio, can significantly enhance the accuracy of assessing obesity. This research, published in Nature, analyzed data from over a decade and more than 844,000 individuals in China, Spain, the U.K., and the U.S.

The team compared obesity diagnoses made using either BMI alone or the new combined framework that incorporates BMI alongside other factors. They found that relying on BMI alone could lead to misclassifications in both directions, misdiagnosing both obesity and the absence of obesity. Moreover, the study revealed that even when excess weight is correctly identified, there is no consensus on the appropriate next steps.

The Lancet Diabetes and Endocrinology Commission, led by Francesco Rubino, proposed a new classification called preclinical obesity, which includes individuals with excess weight who might not require immediate treatment.

Preclinical obesity, distinguished from clinical obesity that demands more immediate interventions like diet, exercise, or specific medications, affects a substantial portion of the population. Around 77% to 91% of preclinical obesity cases did not progress to clinical obesity over a decade. While clinical obesity increases the risk of mortality by 69% during the study period, preclinical obesity raises the risk by 19%.

The implications of this new framework are profound, especially as GLP-1 drugs, which effectively treat obesity, become more prevalent. Accurate diagnostics can guide doctors in counseling patients about their treatment options and dosing decisions, ensuring that therapies are proportionate to individual needs. Rubino emphasizes that the new diagnostic system offers a more nuanced approach, similar to how other medical conditions are diagnosed, with distinct criteria for preclinical and clinical obesity. This approach could revolutionize how doctors manage obesity and its associated health risks.