Hidden fat linked to artery damage challenges BMI as a sole obesity metric
A landmark study led by researchers at McMaster University reveals that hidden fat stored deep within the abdomen and in the liver may quietly harm arteries — even in people who appear healthy. Published in Communications Medicine on October 17, 2025, the findings challenge the long-standing reliance on body-mass index (BMI) as the main gauge of obesity and offer fresh insight into how fat distribution affects cardiovascular health.
What the study did
Using advanced magnetic resonance imaging (MRI) techniques and data from more than 33,000 adults in Canada and the United Kingdom, researchers measured visceral fat (fat surrounding internal organs) and hepatic fat (fat in the liver) and examined their relationship to carotid artery health. The carotid arteries supply blood to the brain, and their thickening or plaque buildup is a well-known predictor of stroke and heart attack.
The study drew on two large cohorts — the Canadian Alliance for Healthy Hearts and Minds (CAHHM) and the UK Biobank — to assess how fat distribution relates to artery structure and function. Importantly, the researchers adjusted for traditional cardiovascular risk factors such as cholesterol and blood pressure to isolate the effect of visceral and liver fat.
Key findings
Researchers found a robust association between visceral fat and carotid plaque buildup and arterial wall thickening. Liver fat also showed a significant, though weaker, link to these arterial changes. Notably, these associations persisted even after accounting for lifestyle factors and metabolic risk indicators, underscoring that hidden fat can independently influence artery health.
As co-lead author Russell de Souza explains, the data suggest that “hidden fat is metabolically active and dangerous; it’s linked to inflammation and artery damage even in people who aren’t visibly overweight.” The corresponding author, Sonia Anand, emphasizes that this fat is not readily detectable through appearance alone, reinforcing the need for more nuanced risk assessment tools.
Why these findings matter for clinical practice
The study’s implications extend beyond academic interest. For clinicians, the results argue for moving past BMI and waist measurements as the sole indicators of cardiovascular risk. Imaging-based assessments of fat distribution — including MRI-based evaluation of visceral and hepatic fat — could become a valuable addition to risk stratification, particularly for middle-aged adults who may look healthy yet harbor harmful hidden fat.
The findings also highlight a potential gap in current screening guidelines. If visceral and liver fat contribute to artery damage independently of traditional risk factors, some patients at risk may be overlooked with standard assessments. This could pave the way for targeted interventions focusing on fat distribution, not just overall body weight.
What the study adds to public understanding
Public awareness about obesity often centers on visible weight, but health risks stem from where fat is stored. Visceral fat wraps around internal organs, while liver fat stores in the liver. Both have been associated with metabolic conditions such as Type 2 diabetes and hypertension; this study extends those concerns to artery integrity, offering a clearer link to stroke and heart disease risk.
As healthcare systems consider integrating imaging into routine risk assessment, clinicians must balance benefits with access, cost, and patient preferences. The researchers acknowledge that MRI scanning is resource-intensive, but they argue that the long-term payoff could be more precise risk prediction and better-targeted prevention strategies.
About the researchers and funding
The study was led by McMaster University’s Russell de Souza and Marie Pigeyre, with support from institutions across Canada and the UK. Funding came from the Canadian Partnership Against Cancer, Heart and Stroke Foundation of Canada, and the Canadian Institutes of Health Research, among others. MRI reading costs were provided in-kind by Sunnybrook Hospital, and Bayer AG supplied IV contrast. Data sources included CAHHM and the PURE Study, reflecting a wide, international collaboration.
Takeaway
Hidden abdominal and liver fat is more than a risk factor for diabetes or hypertension — it may directly influence artery health. For individuals, this means that maintaining a healthy weight remains important, but so does monitoring fat distribution. For clinicians, it signals a need to broaden cardiovascular screening beyond BMI, considering imaging-based insights into fat storage patterns to better prevent strokes and heart attacks.
