Diagnosing obesity by combining organ function and body fat distribution with body mass index yields more accurate classifications than relying on body mass index alone, according to a study published on November 11 in Nature.
The diagnostic framework distinguishes between clinical and preclinical obesity. Researchers compared this system—proposed in 2025 by The Lancet Diabetes & Endocrinology Commission—with traditional body mass index assessments.
Following the Lancet framework makes diagnosing obesity a more complex activity, according to Commission Chair and senior author Francesco Rubino, chair of metabolic and bariatric surgery at King’s College London.
“It’s not different than what we do in other fields of medicine,” Rubino said in a press briefing reported by Medscape, addressing concerns raised by Rothberg.
“A medical history and a physical exam can pick up many, if not most, of the organ dysfunctions; they don’t require sophisticated diagnoses,” Rubino said, adding that clinicians must determine whether organ dysfunction stems from obesity or preceded it.
Lead author An Pan acknowledged at the briefing that determining the origin of organ dysfunction requires additional assessments and clinical judgment.
“These could be challenges, and many clinicians are asking, ‘Do we really need that many organ dysfunction criteria or could we use a smaller number?'” Pan said. “We’re now trying to further refine our criteria and see if we can come up with different versions [of the framework] that can be adapted to clinics which have different resources and capacities.”
Researchers Compare Obesity Definitions Using Mortality and Prevalence Data
To evaluate how the Lancet Commission’s multi-indicator standard stacks up against standard body mass index evaluations, investigators reviewed mortality, prevalence, and incidence figures drawn from 844,108 participants spread across four distinct study groups in Spain, the US, the UK, and China.
Clinical obesity was defined as anthropometric measures like waist circumference or waist-to-hip ratio in addition to body mass index, accompanied by at least one of 18 adult diagnostic criteria representing organ dysfunction or functional impairment across cardiovascular, respiratory, metabolic, hepatic, renal, neurologic, musculoskeletal, reproductive, urologic, and lymphatic systems.
Complementing body mass index with waist circumference and waist-to-height ratio showed that body mass index alone overestimated obesity in 1.2% to 3.1% of participants and underestimated it in 5.2% to 8.6% of participants across the cohorts.
The Lancet Commission’s definition increased overall obesity prevalence by 3.3% to 7.4% relative to body mass index classifications. Clinical obesity accounted for 22.7% to 31.3% of total obesity, yielding an overall population prevalence of 5.6% to 10.9%.
Between 77.4% and 91.3% of individuals with preclinical obesity at baseline showed no progression to clinical obesity over 10 years.
Increased mortality risk was associated with the Lancet Commission’s obesity definition but not with body mass index-only obesity. Clinical obesity linked to substantially higher all-cause mortality with a hazard ratio of 1.69, while preclinical obesity conferred a modest risk with a hazard ratio of 1.19.
“If the data from our study hold to the broader population, you have a significant portion of people classified as having obesity who don’t have the level of excess body fat that causes a risk of mortality [beyond that of] the population without increased body fat,” Rubino said. “Those people effectively are overdiagnosed with a disease.”
Rubino added that the body mass index system is problematic because of its inaccuracy at scale.
“Even the relatively small percentages in large populations can correspond to millions of people being assigned to one or another category and being assessed clinically in a way that doesn’t correspond to their health status,” Rubino said.
Rothberg Argues New Obesity Criteria May Complicate Clinical Practice
Rothberg told Medscape that all prior points of concern raised by her in response to the Commission still apply.
According to Rothberg, demonstrating that excess body fat directly causes organ impairment is hard to put into everyday medical practice and risks leading to delayed care or hurdles in obtaining treatment.
“The rates of misclassification based on BMI are relatively small, and the added complexity hardly seems to warrant changing the definition to include the additional measures,” Rothberg told Medscape. “In addition, the risk of all-cause mortality among people with ‘pre-obesity’ is still 19% higher (as opposed to 69%), but 19% is not negligible.”
“My concerns about withholding treatment from otherwise patients with ‘pre-obesity’ until they develop ‘clinical obesity’ and exacerbating disparities still seem to apply,” she said.