A photo illustration of a broken bathroom scale.

Body mass index (BMI), a widely used but controversial medical metric, is frequently employed to diagnose obesity despite its inherent limitations. A key flaw is its inability to distinguish between fat and muscle mass, and its overall inaccuracy is widely acknowledged.

An international panel of 58 experts across various medical fields proposes a more comprehensive approach to obesity diagnosis in a January 14th *The Lancet Diabetes & Endocrinology* publication. They advocate for supplementing or replacing BMI with additional measurements, such as waist circumference, or objective body fat assessments. While precise body fat measurement methods exist, their higher cost and complexity limit their current usage.

The proposal suggests categorizing obesity into clinical and preclinical stages. Clinical obesity is characterized by health issues stemming from excess body fat, including organ dysfunction and impaired daily activities. Preclinical obesity, conversely, lacks these immediate health complications. Dr. Francesco Rubino, the proposal’s lead author, describes this framework as a significant advancement towards a globally applicable, objective obesity diagnosis.

Rubino terms this framework “the most radical change that has been proposed for the diagnosis of obesity,” highlighting its aim to create “a new diagnosis…that is meant to be objective and pragmatic enough to be globally relevant.” 

Although not mandatory, the proposal has received support from 76 global medical organizations, including prominent groups like the American Heart Association and the World Obesity Federation. 

Dr. Sahar Takkouche, an obesity medicine specialist not involved in the panel, notes that while this “new approach demands a fundamental change in how we treat obesity,” full implementation will face challenges, citing limited access to advanced body composition measurement tools and lagging insurance coverage. Nevertheless, she sees the proposal as offering “new hope for more effective care.” 

Rubino suggests the new criteria can help determine which patients might benefit from treatments like medications or surgery. He explains that while such interventions might be beneficial for those with clinical obesity, preclinical obesity may warrant less intensive treatments, with monitoring alone potentially sufficient in some cases.

“Obesity is nuanced. It’s a spectrum,” Rubino emphasizes. “It’s not a single thing.”

Dr. Tirissa Reid, an endocrinologist and obesity specialist, points out that while many specialists already employ many of the methods recommended in the report, the expert consensus emphasizing that “excess body fat doesn’t necessarily equate with illness automatically” is significant. This could reshape public perception of obesity and assist clinicians in making informed treatment decisions.

A notable debate exists within the medical community regarding the definition of obesity. Organizations like the CDC and the AMA classify it as a disease; however, some clinicians contest this, arguing that it’s an oversimplification. While the link between obesity and chronic health problems is well-documented, the causal relationship requires further research, according to Dr. Lisa Erlanger. She notes that some obese individuals exhibit no chronic conditions and that weight stigma and inadequate healthcare might contribute to negative health outcomes.

Erlanger critiques the new proposal— noting its authorship includes individuals with weight-loss industry ties— as flawed, arguing it equates any impairment associated with excess weight as illness and relies on imprecise metrics like waist circumference to assess the impact of fat cells on symptoms. She further suggests that the medical community’s approach to obesity lacks sufficient investigation into whether it causally influences many of its associated complications, and whether weight loss is always the optimal treatment strategy.

Erlanger highlights the significant positive health impact of lifestyle factors like exercise, nutrition, and sleep, regardless of their effect on weight. Studies demonstrate that cardiorespiratory fitness is a stronger predictor of longevity than weight.

Rubino asserts that the need for refined, accurate methods of assessing obesity and its impact on health is essential, emphasizing that the proposed approach addresses these requirements. “Disease should not be a matter of opinion,” he concludes. “It should be a matter of fact.”

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