You might look healthy on the outside, but deep inside your abdomen, invisible fat could be quietly clogging your arteries. That’s the unsettling takeaway from a new study out of McMaster University that tracked more than 33,000 adults across Canada and the United Kingdom.
The research, published October 17 in Communications Medicine, zeroed in on two types of fat most people never think about: visceral fat, which wraps around internal organs like a thick, metabolically active blanket, and hepatic fat, which accumulates in the liver. Both are linked to diabetes, high blood pressure, and heart disease. But until now, scientists weren’t sure how directly these hidden fat deposits contributed to artery damage, the kind that precedes strokes and heart attacks.
Using advanced MRI scans, researchers measured fat distribution and carotid artery health in the necks of participants. These arteries supply blood to the brain, and when they thicken or develop plaque, the risk of cardiovascular events shoots up. What they found was striking: even after accounting for traditional risk factors like cholesterol, blood pressure, and smoking, visceral and liver fat were still independently associated with artery damage.
“You can’t always tell by looking at someone whether they have visceral or liver fat. This kind of fat is metabolically active and dangerous; it’s linked to inflammation and artery damage even in people who aren’t visibly overweight.”
That quote comes from Sonia Anand, a vascular medicine specialist at Hamilton Health Sciences and corresponding author of the study. She’s talking about the so-called “skinny fat” phenomenon, where someone appears lean but harbors dangerous internal fat deposits. It’s a reminder that body-mass index, or BMI, the go-to metric for assessing obesity, doesn’t tell the whole story.
Why Visceral Fat Is Worse Than You Think
Visceral fat isn’t just sitting there inert. It’s biologically active, secreting inflammatory molecules and hormones that mess with metabolism and promote insulin resistance. The study found that for every one standard deviation increase in visceral fat volume, there was a measurable increase in carotid artery thickness and plaque buildup. In the UK Biobank cohort, that translated to a 0.016 millimeter increase in artery thickness per standard deviation of visceral fat. That might sound trivial, but previous research suggests even a 0.010 millimeter annual reduction in artery thickness lowers cardiovascular disease risk by about 16 percent.
Liver fat showed a weaker but still significant link. For every standard deviation increase in hepatic fat, carotid artery thickness rose by 0.012 millimeters in the UK group. The Canadian data, which used a different imaging technique to measure artery wall volume rather than thickness, showed similar trends, though the association with liver fat was less consistent after adjusting for other risk factors.
Russell de Souza, the study’s co-lead author and an associate professor at McMaster, called the findings a wake-up call. “This study shows that even after accounting for traditional cardiovascular risk factors like cholesterol and blood pressure, visceral and liver fat still contribute to artery damage,” he said. De Souza argues that doctors need to move beyond BMI and waist circumference, and start thinking about fat distribution in a more sophisticated way.
What This Means for Middle-Aged Adults
The study participants were middle-aged, averaging around 54 to 57 years old. Most were white, and the cohorts excluded people with contraindications to MRI scans. The researchers controlled for smoking, alcohol consumption, diabetes, high blood pressure, and cholesterol levels. Still, the association between hidden fat and artery damage persisted.
One possible explanation involves the “fat overflow” theory. When subcutaneous fat storage, the kind just under your skin, reaches capacity, excess fat spills into the visceral cavity. There, it triggers inflammation as immune cells infiltrate bloated fat cells. This cascade of inflammatory signals damages blood vessel walls and accelerates plaque formation. Liver fat may play a related role, promoting the production of small, dense cholesterol particles that are particularly good at burrowing into artery walls.
The findings suggest that imaging-based assessments of fat distribution could become a valuable tool in predicting cardiovascular risk, especially for people who don’t fit the traditional profile of someone at high risk. A person with a normal BMI but high visceral fat could be silently accruing artery damage. Conversely, someone who’s overweight but carries most of their fat subcutaneously may face lower cardiovascular risk than BMI alone would suggest.
For now, the best way to reduce visceral and liver fat remains the same: eat a Mediterranean-style diet rich in fiber, omega-3 fatty acids, and vegetables; avoid processed foods and added sugars; exercise regularly; and maintain a healthy weight. Some newer drugs, like liraglutide, have shown promise in reducing visceral fat, and the FDA recently approved resmetirom for treating advanced liver fat disease. But behavior change is still the frontline defense.
The study’s cross-sectional design means it can’t prove that visceral fat causes artery damage, only that the two are associated. Future research will follow participants over time to see if reducing visceral fat slows or reverses atherosclerosis. For now, though, the message is clear: what you can’t see might be what hurts you most.