A new study suggests that only around one-quarter to one-third of people currently diagnosed with obesity are experiencing obesity-related ill health, raising fresh questions about how the condition should be identified and treated.
The research, published in the journal Nature on Wednesday, argues that relying solely on Body Mass Index (BMI) may not provide an accurate picture of a person’s health.
Instead, researchers propose considering body fat levels, waist measurements and whether excess weight has already affected vital organs before classifying someone as having obesity.
The findings build on a proposal introduced last year by international experts and medical organisations calling for obesity diagnosis to move beyond BMI, which measures weight in relation to height.
The World Health Organization estimates that more than one billion people worldwide are living with obesity, a condition associated with an increased risk of type 2 diabetes, cardiovascular disease, liver and kidney disease, and certain cancers.
The latest study analysed data from nearly 850,000 adults in China, Britain, the United States and Spain to examine how a revised definition could affect obesity diagnoses and treatment.
Researchers estimated that under the proposed framework, between 1% and 3% of people classified as obese using BMI alone would no longer meet the criteria.
Meanwhile, another 5% to 9% of people, including those with higher body fat levels, could newly be diagnosed with the condition. This could affect tens of millions of people worldwide.
The proposed system divides obesity into two categories: pre-clinical obesity and clinical obesity.
Pre-clinical obesity refers to people with excessive body fat who have not yet developed related health problems, while clinical obesity applies to those whose condition has already caused organ dysfunction or other health complications.
Under the framework, doctors would assess body fat through measurements such as waist circumference, alongside BMI.
They would also examine whether excess weight has affected organs such as the heart or liver before making a clinical diagnosis.
People with high BMI but without excessive body fat may therefore no longer automatically be classified as having obesity.
Those with high BMI and excessive body fat but no related organ dysfunction would fall under pre-clinical obesity, while patients experiencing weight-related organ problems would be classified as having clinical obesity and may require more urgent treatment.
The study’s senior author, Francesco Rubino, professor and chair of metabolic and bariatric surgery at King’s College London, said the limitations of BMI measurements had long been recognised.
“But we haven’t so far got a better system,” he said.
Rubino said the proposed framework aimed to provide a more meaningful clinical assessment of obesity that could help guide medical treatment and public health policies.
Across the four countries examined, researchers estimated that only around 27% of people classified as having obesity would meet the criteria for clinical obesity, equivalent to approximately 8.5% of all adults.
The majority of those with pre-clinical obesity also did not progress to clinical obesity, with around 82% remaining without the more serious condition during the study period.
However, progression rates were higher among participants in China and Spain.
The findings add to growing calls for a more comprehensive approach to obesity diagnosis, rather than relying on BMI alone to determine whether someone is experiencing obesity-related health problems.
