"Weight Alone Can't Determine Obesity"... Analysis of 840,000 Validates New Diagnostic Criteria [Reading Science]

Adding waist circumference and organ function assessments to BMI raises obesity prevalence by 3.3-7.4 percentage points
Death risk 69% higher with clinical obesity... Study published in Nature

A study has found that obesity should be assessed not only by body mass index (BMI), calculated using weight and height, but also by waist circumference and organ function.

File photo for illustrative purposes. Courtesy of Pixabay.

An analysis of more than 840,000 adults in four countries found that applying new criteria classified more people as having obesity than the existing criteria did, and that mortality risk varied depending on whether their health had actually been impaired. However, further validation appears necessary to determine whether the new diagnostic system also improves treatment outcomes.

An international research team from China, the United Kingdom, the United States and Spain, among other countries, applied a new obesity diagnostic system proposed by a commission in the international journal The Lancet in 2025 to a large population. The findings were published in the international journal Nature on Nov. 12.

The research team analyzed data from 844,108 adults in four countries. They added measures that can assess body fat distribution, including waist circumference and the waist-to-height ratio (WHtR), to the existing BMI-based obesity classification, and assessed whether obesity was associated with organ dysfunction.

BMI is calculated by dividing weight in kilograms by height in meters squared and is widely used to determine obesity. However, it cannot distinguish the proportions of fat and muscle in a person's weight, and it does not adequately reflect how much fat has accumulated around the abdomen and elsewhere.

AI-generated image.

The new diagnostic system divides obesity into "clinical obesity" and "preclinical obesity." Clinical obesity is a condition in which excess body fat has caused actual problems with organ function or daily activities. Preclinical obesity refers to a condition in which a person has excess body fat but no clear organ dysfunction has yet been identified.

The analysis found that, under the new criteria, obesity prevalence was 3.3 to 7.4 percentage points higher than under the existing BMI-based classification. Some people who were not classified as having obesity based on BMI alone were classified as having obesity when additional body measurements, such as waist circumference, were applied.

Differences were also seen in health risks. The hazard ratio (HR) for death in the clinical obesity group was 1.69. The figure was relatively lower, at 1.19, for the preclinical obesity group, but this still represented a significant increase in mortality risk.

The researchers suggested that prevention and treatment approaches should also differ, since the two groups have different health conditions and future risks.

"Obesity diagnosis should focus on health impairment, not weight"

Experts praised the study for providing evidence to address the limitations of BMI, while stressing that the clinical effectiveness of the new diagnostic system should not be taken for granted.

File photo for illustrative purposes. Photo courtesy of Pixabay.

Lee Sang-yeol, a professor in the Division of Endocrinology and Metabolism and the Digital Health Center at Kyung Hee University College of Medicine, said, "The significance of this study is that it broadens the focus of obesity care from 'how much does a person weigh?' to 'how does excess body fat affect health?'" He added, "It is significant that this approach, which adds waist circumference and organ function assessments to BMI, is supported by data from 840,000 people across four countries."

However, Lee explained, "This is not a newly developed BMI formula, and an increase in prevalence does not mean diagnostic accuracy has improved." He also said it should be taken into account that the clinical obesity group included people who already had organ dysfunction, which helps explain why their mortality risk was higher.

Diego Bellido Guerrero, president of the Spanish Society for the Study of Obesity (SEEDO) and head of endocrinology and nutrition at Ferrol Hospital in Spain, said, "BMI is useful, but it is not sufficient to assess an individual's obesity status. Where fat accumulates and how it affects health are important."

He said, "Even two people with the same BMI can have very different health risks and treatment needs," adding, "Combining waist circumference measurements with assessments of organ function can help provide a better understanding of a patient's health."

However, there were also warnings that the new classification should not immediately lead to changes in treatment guidelines. Bellido Guerrero said, "If a new diagnosis automatically leads to a medication prescription, there is a risk of overdiagnosis and overtreatment." He stressed, "Whether to use medication should be determined by considering the expected benefits and risks, as well as the individual circumstances of the patient."

This was an observational study and did not establish whether treatment based on the new diagnostic system actually reduces complications or mortality. The study also had limitations: the methods for collecting clinical information varied across the populations studied, and it was not determined on an individual basis whether some cases of organ dysfunction were caused by obesity.

Lee said, "Preclinical obesity should not be regarded as a condition without health risks," adding, "Prevention, follow-up monitoring and active treatment when necessary are important." He also stressed, "Before the system can be applied in Korea, its criteria must be validated to reflect the body types and metabolic risks of Koreans."

This content was produced with the assistance of AI translation services.