A major new study suggests that doctors may need to rethink the way obesity is diagnosed. For decades, body mass index, known as BMI, has been the standard tool used to decide whether someone is overweight or obese.
But researchers now say BMI alone may miss many people who are actually at high risk of serious diseases.
Scientists from Lund University and AstraZeneca found that adding waist measurements and body fat percentage gives a much clearer picture of health risks linked to obesity.
Their study was published in eBioMedicine.
Obesity is becoming one of the world’s biggest public health problems. It increases the risk of conditions such as type 2 diabetes, heart disease, kidney disease, high blood pressure, and some cancers.
BMI has been widely used because it is simple and quick. Doctors only need height and weight to calculate it. However, BMI cannot show where fat is located in the body or how much fat a person truly has.
This is important because fat stored around internal organs and the abdomen appears to be especially harmful to health.
In recent years, many scientists have argued that obesity should not be defined by BMI alone. In 2025, experts writing in entity[“academic_journal”,”The Lancet Diabetes & Endocrinology”,”Medical journal”] stated that BMI by itself is not reliable enough for diagnosing obesity.
The new study provides strong support for that idea.
Researchers analyzed information from nearly half a million people in the UK Biobank study. In total, 489,311 participants were included and followed for about 13 years.
Instead of only using BMI, researchers grouped people according to body fat percentage and waist circumference. They divided participants into five risk categories ranging from low risk to very high risk.
The researchers then examined how likely participants were to develop serious health problems over time.
During the study period, more than 24,000 people experienced major cardiovascular events such as heart attacks or strokes. More than 30,000 developed type 2 diabetes, and almost 15,000 developed chronic kidney disease.
The results showed very large differences between the risk groups.
Participants with the highest levels of unhealthy body fat had more than nine times the risk of developing type 2 diabetes compared with people who had healthier body fat profiles.
Their risk of chronic kidney disease was twice as high, and their risk of cardiovascular disease was 64 percent higher.
One of the most surprising findings was that some people with “normal” BMI scores still had dangerous levels of body fat and unhealthy fat distribution.
These individuals would usually not be considered obese using standard BMI measurements. Yet they still faced much higher risks of disease.
Compared with people who had healthy fat distribution, these individuals had a 45 percent higher risk of cardiovascular disease, a 58 percent higher risk of kidney disease, and more than four times the risk of type 2 diabetes.
The researchers say these findings show why relying only on BMI may leave many high-risk people unidentified.
Lead researcher Sophie Gunnarsson explained that measuring both waist circumference and body fat percentage could help doctors better identify people who may benefit from early treatment or prevention strategies.
The researchers believe this could improve decisions about lifestyle programs, obesity medications, and weight-loss surgery.
Researcher Rashmi Prasad from Lund University said the long-term goal is to move toward more individualized obesity care based on a person’s actual disease risk instead of one simple number.
The study also reflects a larger change in how obesity is viewed by the medical community. Increasingly, obesity is being recognized as a complex disease involving metabolism, inflammation, fat distribution, genetics, and organ health.
The researchers acknowledged that most people in the study were of European ancestry, so future studies in more diverse populations will still be important.
Overall, the study provides important evidence that obesity diagnosis may need to become more detailed and personalized. Its greatest strength is the very large number of participants and the long follow-up period.
However, the study also highlights that health risks linked to obesity are more complicated than body weight alone. Future healthcare systems may increasingly use body fat measurements and waist size together with BMI to better identify people at risk before serious diseases develop.
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Source: Lund University.
