Fat Is Not the Enemy: Why the New Obesity Diagnostic Framework Misreads Human Biology

A recent study published in the Annals of Internal Medicine (National Prevalence of Clinical Obesity by BMI Class: A National Cross-Sectional Study - doi.org/10.7326/ANNALS-25-0528) and reported by MedPage Today on June 1 (Obesity With a Normal BMI? Study Suggests It's Common), 2026 has attracted considerable attention. Using the new diagnostic framework proposed by the Lancet Diabetes & Endocrinology Commission, researchers at the University of Southern California found that over 26% of U.S. adults with a normal BMI already meet criteria for clinical obesity. When two or three abnormal body measurements were applied, nearly 78% of all American adults qualified as having excess adiposity. The authors called for broader screening and earlier clinical intervention. The study has been welcomed in some quarters as a long-overdue correction to the limitations of BMI. I read it differently.

A Valid Critique Carrying a Questionable Conclusion

The scientific critique of BMI is legitimate. Body mass index measures total weight relative to height, not fat specifically. A heavily muscled athlete can register as obese; a sedentary person with significant visceral adiposity can register as normal. This is a real diagnostic limitation, well documented over decades. On this point, the study's authors are correct.

But a valid critique of one diagnostic tool does not automatically validate the framework proposed to replace it. The Lancet Commission's criteria expand the definition of clinical obesity to include anyone with excess adiposity — now measured by waist circumference, waist-to-hip ratio, or direct fat mass assessment — combined with any obesity-related organ or physical dysfunction, including hypertension, knee pain, or chronic fatigue. Under this definition, the pool of Americans eligible for pharmacological treatment, including GLP-1 receptor agonists, expands by tens of millions. The study's authors acknowledge that outcome data justifying intervention in this newly defined population does not yet exist.

What the Framework Forgets

The more fundamental problem is biological. Adipose tissue is not a pathological substance awaiting removal. It is a metabolically active organ performing functions that are essential to life. Fat tissue stores and mobilizes energy across feeding and fasting cycles. It secretes leptin, adiponectin, and other hormones that regulate appetite, insulin sensitivity, and immune response. It provides mechanical protection to organs and joints. It participates in thermal regulation and reproductive function. Sufficient fat mass is a requirement of normal physiology, not a deviation from it.

The diagnostic framework treats fat quantity above a statistical threshold as inherently suspect. But adipose tissue pathology is not simply a matter of how much fat a person carries. It is a matter of whether that tissue is functioning normally — whether it is inflamed, hypoxic, insulin-resistant, or infiltrated with dysfunctional macrophages. Visceral fat in a state of metabolic dysfunction behaves very differently from subcutaneous fat in a metabolically healthy individual. The tissue is the same. The pathological state is not.

The Question the Study Does Not Ask

A biologically honest diagnostic approach would not ask how much fat a person has relative to a population norm. It would ask whether a given person's adipose tissue is performing its necessary functions, whether dysfunction is present and specifically attributable to adipose pathology, and critically, whether fat accumulation is driving clinical dysfunction or whether both are downstream consequences of a deeper metabolic dysregulation — chronic inflammation, insulin resistance, sedentary physiology — in which adipose tissue is a bystander rather than a cause.

My Conclusion

Expanding the diagnostic category of obesity without this biological precision does not improve clinical care. It medicalizes normal variation, conflates statistical excess with pathological dysfunction, and — given the timing — conveniently enlarges the population eligible for expensive pharmacological treatment before outcome evidence justifies doing so. Better diagnosis of obesity-related metabolic dysfunction is genuinely needed. But it requires understanding fat as a tissue with necessary functions, not as a substance to be measured, classified, and eliminated.

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Mykola Iabluchanskyi Yabluchansky