A new study led by researchers at McMaster University reveals that hidden fat deep inside the abdomen and liver may quietly damage arteries, even in people who appear healthy.
The findings, published in Communications Medicine on October 17, 2025, challenge the long-standing reliance on body-mass index (BMI) as a measure of obesity and offer fresh insight into how hidden fat contributes to heart disease.
Visceral fat (the kind that wraps around internal organs) and hepatic fat (fat stored in the liver) are known to increase Type 2 diabetes, high blood pressure, and heart disease risk – but their effects on artery health was less known.
Using advanced MRI imaging and data from over 33,000 adults in Canada and the United Kingdom, researchers found that visceral and hepatic fat are strongly linked to the thickening and clogging of carotid arteries in the neck. These arteries supply blood to the brain, and their narrowing is a key predictor of stroke and heart attack.
"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," says Russell de Souza , co-lead author of the study and associate professor in the Department of Health Research Methods, Evidence, and Impact at McMaster.
"The findings are a wake-up call for clinicians and the public alike," says de Souza, a faculty member in the Mary Heersink School of Global Health and Social Medicine, and member of the Centre for Metabolism, Obesity and Diabetes Research (MODR) and at McMaster. de Souza led the study with Marie Pigeyre , associate professor in the Department of Medicine at McMaster.
The research team analyzed data from two major cohorts: the Canadian Alliance for Healthy Hearts and Minds (CAHHM) and the UK Biobank, using MRI scans to measure fat distribution and artery health. They found that visceral fat was consistently associated with carotid plaque buildup and artery wall thickening, while liver fat showed a weaker but still significant link. Importantly, these associations held even after the researchers adjusted for lifestyle and metabolic risk factors.
The implications are far-reaching. For clinicians, it underscores the need to go beyond BMI and waist circumference and consider imaging-based assessments of fat distribution. For middle-aged adults, it's a reminder that hidden fat, not just visible weight, can silently increase cardiovascular risk.
"You can't always tell by looking at someone whether they have visceral or liver fat," says Sonia Anand , corresponding author of the study, a vascular medicine specialist at Hamilton Health Sciences and professor in the Department of Medicine at McMaster. "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's why it's so important to rethink how we assess obesity and cardiovascular risk."
This research was supported by the Canadian Partnership Against Cancer, Heart and Stroke Foundation of Canada, and the Canadian Institutes of Health Research, with additional contributions from the Population Health Research Institute, Montreal Heart Institute, Sunnybrook Health Sciences Centre, and others. MRI reading costs were supported in-kind by Sunnybrook Hospital, and Bayer AG provided IV contrast. The study also drew on data from the Canadian Partnership for Tomorrow's Health and the PURE Study.
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