Impact of the 2025 Lancet Diagnostic Criteria on Obesity Treatment in the United States

For decades, clinicians have diagnosed obesity using body mass index (BMI). In January 2025, the updated Lancet guideline recommended the use of anthropometric index in addition to BMI. It also recommended routine treatment for clinical obesity, that is those with organ dysfunction or activity limitations, but for preclinical obesity, only treatment based on individual risk-benefit assessment. The objective of this study is to evaluate how the guideline could change obesity management on a national level. In this cross-sectional study, we projected the 2025 Lancet guideline onto the 2021-2023 National Health and Nutrition Examination Survey (NHANES), a nationally representative population survey. We characterised the change in treatment recommendation that would occur if the Lancet guideline replaced current treatment guidelines. According to the Lancet guideline, the national prevalence of obesity was about 39.6 (1.8) %. The addition of the anthropometric index did not alter obesity diagnosis in most participants, as 96.8 (0.5) % of participants with a BMI > 30 kg/m2 also had elevated waist circumference. Approximately 80.3 (1.2) % of participants with obesity were classified as having clinical obesity. There is a large discrepancy between current medical guidelines and the Lancet guideline. Approximately 41.3% ± 1.2% of people who fit the indication for pharmaceutical treatment do not have clinical obesity, according to the Lancet guideline. Although the Lancet guideline would not alter obesity diagnosis for most people, it would encourage providers to take a more individual-based and multi-organ approach to managing obesity.