Under a new definition of obesity, half of overweight US adults have "clinical obesity"

Short Answer

In 2025, the Lancet Diabetes & Endocrinology Commission proposed defining obesity not by body mass index (BMI) alone but by a measure that reflects body fat, such as waist circumference, together with related organ dysfunction. When this definition was applied to data from 5,642 adults in the US, about half of those who were overweight by BMI and about a quarter of those with normal weight met the "clinical obesity" criterion. This definition is not yet an official diagnostic criterion in the US or in Türkiye.

What was found?

Brian P. Lee and colleagues at Keck Medicine of USC analyzed data from 5,642 non-pregnant adults examined during the 2021–2023 cycle of the US National Health and Nutrition Examination Survey (NHANES) (Annals of Internal Medicine, 2026). After adjustment for age, sex and ethnicity, clinical obesity was found in:

• 26.1% of those with normal BMI
• 50.3% of those who were overweight by BMI
• Higher rates as BMI increased; about 85% in the most severe obesity group

What does the new definition say?

• Clinical obesity: excess adipose tissue and related organ or functional impairment (e.g., sleep apnea, heart failure, joint limitation, high blood sugar). It is defined as a disease requiring treatment.
• Preclinical obesity: excess fat is present, but organ function is not yet impaired; risk reduction and monitoring are recommended.
• Waist circumference alone does not establish a diagnosis. It corrects the picture in cases where BMI may show people with excess abdominal fat as "normal" and people with high muscle mass as "obese."

Evidence label

Study type	Cross-sectional analysis (single time point)
Participants	5,642 adults, US (NHANES 2021–2023)
Human / animal	Human
Peer-reviewed	Yes, Annals of Internal Medicine, 2026

Limitations

• NHANES does not collect all the organ function criteria on the Commission's list; the true rates may be higher.
• The new definition framework has not yet been diagnostically validated.
• The results apply to the US population; they cannot be directly applied to Türkiye.

What does it mean in Türkiye?

• The obesity guideline of the Society of Endocrinology and Metabolism of Turkey (TEMD) recommends measuring waist circumference in addition to BMI during assessment.
• Even if your BMI is in the normal or overweight range, if your waist circumference is high, talk to your family physician about screening for blood sugar, blood pressure and cholesterol.

This content is for informational purposes and does not replace individual medical advice. Consult your physician for an assessment of weight and metabolic risk.