BMI, waist measures best recent obesity criteria

Clinical takeaway: Do not rely on BMI alone when excess adiposity is a concern. Waist circumference can improve routine identification without adding hip circumference to calculate a waist-to-hip ratio.

An obesity measure needs to catch excess adiposity without inadvertently labeling too many patients who do not have it. It also has to be simple enough to use consistently. A recent Lancet obesity definition adds waist-to-hip ratios to body mass index (BMI), but whether that complexity improves classification has been uncertain.

To test whether the added measurements improve identification, investigators conducted a diagnostic accuracy study comparing five anthropometric definitions against whole-body dual-energy x-ray absorptiometry (DEXA) in 1,900 nonpregnant US adults aged 20 to 59 years from the 2017 to 2018 National Health and Nutrition Examination Survey.

The full Lancet definition identified more adults with DEXA-defined excess adiposity than BMI or waist circumference, 87.7% versus 74.0%, but it correctly ruled out excess adiposity in fewer adults without it, 70.7% versus 89.5%. Waist circumference alone and the Lancet definition without waist-to-hip ratio both performed similarly to the BMI-or-waist approach. BMI alone identified only 51.3% of DEXA-defined cases.

The same pattern held for visceral adiposity: the full Lancet definition identified more cases but correctly ruled it out less often than BMI or waist circumference.

DEXA-defined excess adiposity was total body fat of at least 25% in males and 35% in females. Investigators compared the full Lancet definition with four simpler approaches: the Lancet definition without waist-to-hip ratio, BMI or waist circumference, waist circumference alone, and BMI alone. They repeated the comparison using DEXA-defined visceral adiposity.

The clinical task should determine the measure: the full Lancet definition may be more useful for surveillance, where missing cases matters most, while simpler approaches better limit false-positive labeling in individual care. Because these approaches performed less well in men, waist and waist-to-hip cutoffs may need recalibration. The study did not assess the Lancet distinction between clinical and preclinical obesity.

“For clinical practice and individual-level decision-making, where specificity, appropriate resource use, and avoidance of diagnostic labeling harms are paramount, we recommend BMI-or-WC or WC-alone definitions, which offer the best balance of sensitivity and specificity, with substantially fewer false positives than the full Lancet definition,” the authors conclude.

Source: Visaria, et al. (2026 Aug 7) JAMA Netw Open. Lancet Definition vs Other Criteria for Obesity Diagnosis in Adults