For many years, doctors have mainly used body mass index, or BMI, to determine whether a person has obesity. BMI is calculated using a person’s height and weight and has become one of the most common tools for measuring body size around the world.
However, scientists have increasingly questioned whether BMI alone gives a full picture of a person’s health. Two people can have the same BMI while having very different amounts of body fat, different fat distribution, and very different risks for diseases such as diabetes and heart disease.
Now, a large new study from researchers at Lund University and AstraZeneca suggests that doctors may need to move beyond BMI when diagnosing obesity and evaluating health risks.
The study was published in the journal eBioMedicine.
The findings add to growing evidence that obesity is much more complex than simply body weight alone.
In recent years, researchers and medical experts have argued that BMI has important limitations. BMI cannot show how much body fat a person actually has, where that fat is stored, or how it affects the body. It also cannot distinguish between fat and muscle.
For example, some people may have a “normal” BMI but still carry dangerous amounts of fat around the waist and internal organs. Others may have a higher BMI because of greater muscle mass rather than unhealthy fat levels.
In 2025, a major commission of experts published new obesity criteria in The Lancet Diabetes & Endocrinology, arguing that BMI alone should no longer be relied upon to diagnose obesity.
The new study supports this growing shift.
Researchers analyzed health data from 489,311 adults participating in the large UK Biobank study. Participants were followed for a median of 13 years.
Instead of relying only on BMI, the researchers combined measurements of body fat percentage and waist circumference to classify people into five different risk groups.
Waist circumference is important because fat stored around the abdomen is strongly linked to inflammation, insulin resistance, heart disease, and diabetes.
The researchers then studied how these groups differed in their risk of developing major health problems, including cardiovascular disease, type 2 diabetes, and chronic kidney disease.
The results were striking.
Over the study period, 24,778 participants experienced cardiovascular events such as heart attacks or strokes. More than 30,000 developed type 2 diabetes, and nearly 15,000 developed chronic kidney disease.
People in the highest-risk group had dramatically higher disease risks compared with those with healthy body fat profiles.
Compared to the healthiest group, participants in the highest-risk category had more than nine times the risk of developing type 2 diabetes. Their risk of chronic kidney disease was about twice as high, and their risk of cardiovascular disease was 64 percent higher.
One of the most important findings was that many high-risk individuals would have been missed if doctors only looked at BMI.
Some participants had BMI values considered normal but still had unhealthy body fat distribution and high body fat percentages. Even though these individuals would not traditionally be classified as having obesity, they still faced major health risks.
Compared with people who had healthy body fat profiles, these individuals had a 45 percent higher risk of cardiovascular disease, a 58 percent higher risk of chronic kidney disease, and more than four times the risk of type 2 diabetes.
Lead researcher Sophie Gunnarsson explained that combining body fat percentage and waist circumference may help doctors identify high-risk individuals much earlier.
The researchers believe this approach could improve screening programs and help doctors decide who may benefit most from lifestyle changes, weight-loss medications, or bariatric surgery.
Researcher Rashmi Prasad from Lund University said the long-term goal is to create more personalized obesity treatment plans instead of relying on one simple measurement for everyone.
The researchers also emphasized that obesity is increasingly being recognized as a disease involving many different biological and metabolic factors, not simply body size.
The study does have limitations. Most participants were of European background, so researchers say more studies are needed in other populations to confirm whether the findings apply equally across different ethnic groups.
Still, the study provides strong evidence that BMI alone may overlook many people at serious risk for obesity-related diseases. One major strength of the research is the extremely large number of participants followed over many years.
The findings support a growing movement toward more individualized and precise approaches to obesity diagnosis and treatment rather than relying only on weight and height measurements.
If you care about weight loss, please read studies that hop extract could reduce belly fat in overweight people, and early time-restricted eating could help lose weight .
For more health information, please see recent studies that Mediterranean diet can reduce belly fat much better, and Keto diet could help control body weight and blood sugar in diabetes.
Source: Lund University.
