A large new study from McMaster University has revealed that fat stored deep in the body, such as around the organs and in the liver, can quietly damage arteries—even in people who appear healthy.
This surprising finding challenges the way we currently measure obesity and heart risk, especially the common use of BMI (body-mass index). The study was published on October 17, 2025, in the journal Communications Medicine.
Most people are familiar with BMI, which is a simple number based on a person’s height and weight. It’s often used by doctors to decide if someone is overweight or obese.
But this study shows that BMI doesn’t tell the full story. Some people with a normal BMI may still carry dangerous fat inside their bodies, which can put them at risk for heart disease.
The researchers used advanced MRI scans to look at more than 33,000 adults in Canada and the UK. They were especially interested in two types of fat: visceral fat, which surrounds organs deep in the belly, and liver fat, which builds up inside the liver.
Both of these types of fat have already been linked to diseases like Type 2 diabetes and high blood pressure. But this study is one of the first to clearly show how they can damage arteries directly.
The scientists focused on the carotid arteries, which run along the sides of the neck and carry blood to the brain. If these arteries become clogged or narrowed, it can lead to strokes or heart attacks.
The MRI scans showed that people with more visceral and liver fat had more thickening and buildup in these arteries—even when their blood pressure and cholesterol levels were normal.
Dr. Russell de Souza, who helped lead the study, explained that this kind of hidden fat is dangerous because it causes inflammation and damages the blood vessels. He said the results are a “wake-up call” for both doctors and patients. Just because someone looks healthy or has a normal weight doesn’t mean they’re safe from heart problems.
The study used data from two major research projects: the Canadian Alliance for Healthy Hearts and Minds and the UK Biobank. The team carefully looked at how fat was distributed in the body and how this affected artery health. Even after accounting for people’s diet, exercise, and cholesterol levels, the link between hidden fat and artery damage remained strong.
This means doctors may need to rethink how they judge heart disease risk. Instead of just looking at BMI or waist size, they might need to use imaging tests that can show where fat is stored in the body. These tests could help find problems early, even in people who don’t show obvious signs of being overweight.
For people in their middle years, this study is a powerful reminder that being slim doesn’t always mean being healthy. The real danger may be fat that is hiding inside, where it can quietly hurt the heart and blood vessels. Dr. Sonia Anand, another author of the study, said, “You can’t always tell just by looking at someone whether they’re at risk.”
The study was funded by several major health organizations in Canada, including the Heart and Stroke Foundation and the Canadian Institutes of Health Research. Many hospitals and research centers also helped make the study possible.
This research gives doctors and patients important new tools to understand and manage heart health. It shows that we may need to look deeper—literally—to truly know who’s at risk for serious disease.
If you care about heart health, please read studies about top foods to love for a stronger heart, and why oranges may help fight obesity, diabetes, and heart disease.
For more health information, please see recent studies about simple guide to a 7-day diabetes meal plan, and why you should add black beans to your plate.
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