BMI has long been used as a simple way to screen for weight-related health risk, but a new study adds to growing evidence that the number can miss important parts of the picture.
In a large study of nearly 490,000 UK Biobank participants, researchers found that combining waist circumference with body fat percentage helped identify people at higher risk of type 2 diabetes, cardiovascular events and chronic kidney disease. Some of those people did not have obesity based on BMI alone.
The findings, published in eBioMedicine, do not mean BMI is useless. BMI is easy to calculate and can still help flag population-level health patterns. But the study suggests that looking only at height and weight may overlook where body fat is carried and how much body fat a person has, both of which may matter for long-term metabolic health.
“Obesity is increasingly recognized as a disease, but BMI is often used alone when diagnosing obesity without considering broader health. The method has several limitations, and our study provides new evidence that integrating body fat percentage and waist circumference captures risk dimensions missed by BMI alone,” said Sophie Gunnarsson, an industrial PhD student at Lund University Diabetes Centre and employee of AstraZeneca.
The researchers analyzed data from 489,311 people in the UK Biobank study and followed them for a median of 13 years. Instead of using BMI alone, they sorted participants into five groups based on body fat percentage and waist circumference, with each group representing a different adiposity profile.
Adiposity refers to the amount and distribution of body fat. In plain terms, the study looked at both how much body fat people had and whether they carried more of it around the waist.
During follow-up, 24,778 participants had a major cardiovascular event, which included cardiovascular death, nonfatal heart attack or nonfatal stroke. Another 30,376 were diagnosed with type 2 diabetes, and 14,906 developed chronic kidney disease, according to Lund University.
Compared with participants in the lowest-risk group, those in the highest-risk group had more than nine times the risk of type 2 diabetes, twice the risk of chronic kidney disease and a 64% higher risk of major cardiovascular events.
The study also found that some people had a higher-risk body fat and waist profile even though their BMI did not fall in the obesity range. Compared with people who had healthier adiposity profiles, those participants had a 45% higher risk of cardiovascular events, a 58% higher risk of chronic kidney disease and more than four times the risk of type 2 diabetes.
That is the key point for everyday readers: BMI can look normal or less concerning while other measures suggest higher metabolic risk.
“Our analyses show that combining body fat percentage and waist circumference when screening for obesity can help us identify individuals at high risk of developing obesity-related diseases that may be missed by using BMI alone,” Gunnarsson said.
Waist circumference may be especially useful because it can reflect central body fat, which is more closely tied to metabolic risk than weight alone. Body fat percentage can also add context that BMI cannot provide, since BMI does not distinguish fat from muscle or show where fat is stored.
Still, the findings should be interpreted carefully. This was an observational study, so it can show that certain body fat and waist profiles were linked to later disease risk, but it cannot prove that the measurements caused those outcomes or that changing one measurement alone would reduce risk.
The study also used UK Biobank data, and the authors noted that most participants were of European origin. That means the findings may not apply equally across all racial, ethnic or geographic groups.
There is also an industry connection worth noting. The study was conducted by researchers at Lund University and AstraZeneca, and the paper reported that the four authors hold stock in AstraZeneca. Rashmi B. Prasad also holds stock in Novo Nordisk. Both companies are active in areas related to cardiometabolic disease and obesity treatment, so those disclosures are relevant when weighing the findings.
The broader message, though, is consistent with a growing shift in how researchers and clinicians think about body size and health. In 2025, a commission published in The Lancet Diabetes & Endocrinology argued that BMI alone should not be used as the sole measure for diagnosing obesity, partly because it does not capture body composition, fat distribution or signs of impaired health.
The study was supported by the SciLifeLab and Wallenberg Data-Driven Life Science Program, the Knut and Alice Wallenberg Foundation, the Swedish Research Council and Vinnova.