BMI

Aiya Almogaber, PharmD

For decades, BMI has been the go-to measure for defining obesity. But a recent report, published on January 14, 2025, in The Lancet Diabetes & Endocrinology and endorsed by 76 global organizations, suggested that BMI alone is an outdated metric that fails to capture the complexity of obesity. The report authors argue for a new definition that considers body fat levels and related health complications, a shift that could have major implications for medical treatment, insurance coverage, and the use of weight loss medications such as Wegovy and Zepbound.

Why BMI falls short

BMI is a simple calculation based on height and weight, widely used in clinical practice because it’s quick and easy to assess. However, it has long been criticized as the measurement tends to lump together individuals with vastly different health profiles. BMI does not distinguish between fat and muscle, nor does it account for fat distribution or metabolic health.

Some patients who may be classified as obese based on BMI may actually be metabolically healthy, while others with a “normal” BMI might have dangerous levels of visceral fat, which increases the risk of diabetes, heart disease, and other chronic conditions.

A new framework for defining obesity

The report, developed by an international commission of 58 experts, proposed a two-tiered system for classifying obesity.

The first tier was preclinical obesity, which was defined as individuals who have excessive body fat but no related medical conditions. These individuals may not require immediate intervention but should be monitored to prevent future health issues.

The second tier proposed by the commission was clinical obesity, defined as individuals with excessive body fat who also experience complications such as metabolic disorders, heart failure, joint pain, or organ dysfunction. These individuals would be prioritized for medical treatment.

Instead of relying solely on BMI, the commission recommended waist circumference measurements as a more accurate screening tool. According to the new guidelines, a waist circumference exceeding 34.6 inches in women and 40 inches in men is a strong indicator of excess fat accumulation.

How this could change obesity treatment

If widely adopted, this new approach could reshape health care policies and treatment protocols. Key areas of impact include access to weight loss medications, physician decision making, and public perception and stigma.

Currently, insurance coverage for medications such as semaglutide and tirzepatide is often tied to BMI thresholds. A more nuanced definition of obesity could lead to revised guidelines on who qualifies for treatment. Physicians may rely on additional diagnostic tools, such as DEXA scans or waist-to-hip ratios, to assess obesity severity beyond BMI. Experts hope that shifting the focus from weight alone to a broader health-based approach could help reduce stigma associated with obesity and reinforce that obesity is a complex medical condition rather than a personal failure.

Challenges and concerns

Despite the potential benefits of this proposed new system, some experts are skeptical about the ease of implementation of this reclassification of obesity. BMI measurements are deeply ingrained in the medical practice space. Changing the way obesity is defined would require significant shifts in clinical guidelines, research parameters, and health care reimbursement policies.

Others worry that the new framework could delay obesity treatment for some patients. David Nathan, MD, a Harvard professor and diabetes expert, cautioned that waiting until complications arise may not be the best approach. “As they would have it, you wouldn’t treat hypertension until the person has a stroke,” he said.

What’s next?

While BMI isn’t disappearing anytime soon, this report adds momentum to the growing call for a more precise and individualized approach to obesity diagnosis. Future studies and policy changes will determine whether these recommendations gain traction in clinical practice or remain a theoretical shift in the conversation around obesity. ■