Scientists have tested the criteria for the diagnosis of obesity on the data of 844 thousand people.

In four groups of adults from China, the UK, the USA and Spain, the proportion of people with signs of obesity increased by 3.3–7.4 percentage points when waist measurements were added to the body mass index. Participants who had excess adipose tissue combined with organ malfunction had a higher risk of death during the follow-up period. This was reported by the journal Nature, which published an analysis of the data of 844,108 people. About whom the usual indicator misses and how clinical obesity differs from preclinical obesity is in the Izvestia article.

Why was the waist measurement added to the body mass index?

Body mass index (BMI) is obtained by dividing weight in kilograms by the square of height in meters. It is convenient to calculate it during a routine examination and use it in large studies. At the same time, two people with the same index may have a different ratio of muscle and fat tissue. In addition, the indicator does not take into account exactly where fat accumulates in the body.

In 2025, The Lancet Diabetes & Endocrinology international commission proposed assessing obesity in two stages. First, the doctor confirms the excess of adipose tissue. The measurement of waist circumference, its relation to height, or an assessment of body composition, if possible, helps in this. The doctor then checks whether excess fat disrupts the functioning of organs or restricts daily activity. In such cases, the commission suggests talking about clinical obesity, and with preserved function, about preclinical obesity.

Who's score has been changed by additional measurements

The researchers tested the proposed scheme on four large datasets. They included participants from the Chinese Kailuan project, the British biobank UK Biobank, the American All of Us program, and the Spanish primary care database SIDIAP. The largest group was British, with over 436,000 members.

With a BMI of 40 kg/m2 or more, no additional measurements were required in the study to confirm excess fat. If the BMI was in the obese range, but below 40 kg/m2, one of the two increased indicators was sufficient — waist circumference or its ratio to height. If the BMI corresponded to overweight, both indicators had to exceed the threshold. The boundaries depended on gender and took into account the characteristics of different populations.

The grades varied in both directions. In different cohorts, from 5.2 to 8.6% of the participants were classified as overweight by one BMI, and obese by the totality of measurements. The reverse discrepancy affected 1.2–3.1% of the participants. Their body mass index corresponded to obesity, but additional measurements did not confirm this.

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After recalculation, the proportion of obese people in the British group increased from 24 to 27.3%, in the Spanish group — from 18.7 to 26.1%. These are estimates for specific groups. The cohorts differed in the way they recruited participants. For example, the Chinese project was formed on the basis of an industrial group, while the Spanish project used records from primary care institutions.

How does clinical obesity differ from preclinical obesity?

In the medical data, the researchers searched for 18 signs of disorders that may be associated with obesity. Among them were obstructive sleep apnea, heart and kidney disorders, as well as restrictions on daily activity. The same violation can have several causes. For example, high blood pressure in an obese person may depend on other factors. When making a diagnosis, the doctor needs to assess how likely it is that the disorder is associated with excess adipose tissue.

To assess the prevalence of clinical obesity, the authors statistically took into account that such disorders also occur in people without obesity. After this correction, the proportion of clinical form among obese participants was estimated at 22.7–31.3%, depending on the cohort. The method provides an estimate for the group. When making a diagnosis for a particular patient, the doctor needs to find out what causes the disorders.

In three cohorts, the transition from the preclinical to the clinical form was assessed over ten years. According to the authors' calculations, it occurred in 8.7% of participants with preclinical obesity in the British group, 21.2% in the Chinese group and 22.6% in the Spanish group. In the American group, the follow-up period was shorter. In four years, the figure was 8.5%.

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What did the mortality data show?

The mortality analysis included three cohorts with a fairly long follow-up. In the group where excess adipose tissue was combined with organ dysfunction according to the proposed criteria, the relative risk of death from all causes in the statistical model was 69% higher than in participants without both signs. With an excess of adipose tissue without detected abnormalities, it was higher by 19%. The American cohort was excluded from this comparison due to the shorter follow-up period.

The work has a limitation that is important for practice. The condition of the organs was assessed based on previously collected data, including diagnoses recorded in medical records. The set of available indicators differed between the cohorts. The authors consider the next step to be research in which doctors will apply uniform criteria at checkups and check how well they predict health changes.

In Russian clinical guidelines, BMI is used in the diagnosis of obesity, and waist circumference is measured to assess abdominal obesity. The International Commission proposes to find out separately whether excess adipose tissue disrupts the body's functioning. According to the authors, in the clinical form, this assessment will help to choose care based on existing disorders. With preserved organ function, the intensity of prevention is proposed to be determined by individual risk, which may vary even with the same weight and waist indicators.