Where You Carry Fat Could Change How Old Your Heart Acts

Where you carry your fat can dictate your cardiovascular age. (© Pixel-Shot – stock.adobe.com)

LONDON — We’ve all heard that carrying extra pounds can hurt your heart. But a massive new study suggests the story is more complicated, and in some ways, surprising. It’s not just how much fat you have that matters, but where your body stores it. And when it comes to heart health, the rules are not the same for men and women.

Researchers from Imperial College London and King’s College London analyzed MRI scans from more than 21,000 adults in the UK Biobank, a large health research project. They wanted to see how different types of fat, including deep belly fat, fat in muscles, fat around the liver, and fat in the hips and thighs, related to “cardiovascular age.” That’s a measure of how old the heart and blood vessels appear compared to someone’s actual age. A 50-year-old could have a cardiovascular system that looks 60 (or 40) depending on their fat distribution.

“Cardiovascular aging is a progressive loss of physiological reserve, modified by environmental and genetic risk factors, that contributes to multi-morbidity due to accumulated damage across diverse cell types, tissues, and organs,” the authors write in their paper, published in The European Heart Journal.

The results point to a clear message: visceral fat, the hidden fat that wraps around internal organs, is consistently linked to an older-looking cardiovascular system in both men and women. But other fat deposits tell a more complicated story, especially for women.

Why Belly Fat Is More Than Skin Deep

The most harmful fat turned out to be the kind you can’t pinch. Visceral fat sits deep in the abdomen and isn’t always obvious from the outside. Unlike fat just under the skin, visceral fat is part of a metabolically active organ system. Adipose tissue stores energy but also secretes hormones, cytokines, and other signaling molecules. When this signaling is abnormal, it can promote inflammation and strain the cardiovascular system.

In this study, more visceral fat was strongly associated with an older cardiovascular age in both sexes. Muscle fat infiltration, which is when fat seeps into muscle tissue, and liver fat were also unfavorable, showing consistent links to cardiovascular systems that looked older than expected.

A Tale Of Two Sexes

Where the findings get especially interesting is when men and women are compared. For men, increases in abdominal subcutaneous fat (just under the skin of the belly) and android fat (the classic apple-shaped distribution) were linked to an older cardiovascular age.

For women, the picture was more mixed. Visceral, liver, and muscle fat were harmful in women just as in men. But gynoid fat, the kind stored around hips and thighs, showed a protective pattern before menopause. Pre-menopausal women with more gynoid fat tended to have younger cardiovascular ages than peers with less, suggesting this fat distribution might help shield the heart. After menopause, that protective effect disappeared, aligning with the known rise in heart disease risk when estrogen levels drop.

The researchers also found that estradiol, the main form of estrogen in women, was linked with less cardiovascular aging in pre-menopausal participants, supporting the idea that hormones influence how fat affects the heart.

One caveat: while the observational model hinted that gynoid fat was linked to higher cardiovascular age in men, the statistical test was not significant. In other words, the study cannot conclude that gynoid fat harms men’s hearts. It only showed a non-significant trend. So the stronger takeaway is that android and abdominal fat matter more for men.

“We have known about the apple and pear distinction in body fat, but it hasn’t been clear how it leads to poor health outcomes. Our research shows that ‘bad’ fat, hidden deep around the organs, accelerates aging of the heart. But some types of fat could protect against aging, specifically fat around the hips and thighs in women,” says Professor Declan O’Regan, who led the research at the MRC Laboratory of Medical Sciences and Imperial College London, in a statement. “We also showed that BMI wasn’t a good way of predicting heart age which underscores the importance of knowing where fat is stored in the body and not just total body weight.”

BMI Misses The Mark With Body Fat

One of the most striking findings was how poorly BMI (body mass index) captured true cardiovascular risk. BMI is easy to calculate, but it lumps muscle and fat together. Two people with the same BMI could have very different heart risks depending on fat distribution.

When the researchers compared BMI classifications with MRI-based measurements, they found clear mismatches:

• Among overweight women, 31% actually had a normal whole-body fat percentage.
• Among overweight men, 11% were reclassified as normal fat mass.
• Another 23% of overweight men were reclassified into the obese range.

These findings show how BMI can be misleading. A muscular athlete and a sedentary worker could both have a BMI of 28, yet their heart risks would differ sharply depending on whether their weight came from muscle or visceral fat.

What This Means For Your Health

The take-home message isn’t that BMI is useless, but that fat distribution matters more than we’ve appreciated. Carrying weight in the belly—especially visceral fat—is particularly risky. Meanwhile, fat on the hips and thighs isn’t necessarily a bad thing for pre-menopausal women and may even be protective.

The study also explored how common medications might influence this relationship. Among participants with diabetes, those taking metformin had smaller associations between harmful fat deposits and cardiovascular aging. The effect was modest, but it suggests metformin could lessen fat’s impact on the heart.

In the discussion, the authors also pointed to GLP-1 receptor agonists, a newer class of diabetes and weight-loss drugs, as a promising target for future research. These drugs have been shown to reduce visceral and liver fat and may help regulate inflammatory signals. However, this study did not test those medications directly, so their role remains speculative.

A Few Important Caveats

Like all research, this study has limits. Most participants were White and from relatively less deprived backgrounds, so the findings may not apply equally to all populations. The data also came from a single time point, meaning it cannot show how changes in fat distribution over years affect cardiovascular aging. And while the cardiovascular age model was validated, it was trained on generally healthy people, which may not reflect outcomes in those with existing disease.

Still, this is one of the largest and most detailed looks yet at how fat distribution links to heart health. It supports the idea that where you store fat can matter more than how much you weigh overall.

Fight The Fat: What You Can Do

While none of us can control our hormones or genetic predispositions, lifestyle choices still matter. Regular physical activity, balanced nutrition, and keeping blood sugar in check all help reduce visceral fat. Paying attention to waist circumference may provide more insight into cardiovascular risk than BMI alone.

As imaging technologies become cheaper and more widely available, doctors may eventually use detailed body-fat scans as part of routine check-ups, helping catch people whose hearts look “older” than their years even if their BMI seems ordinary. Until then, the best advice is familiar: keep moving, eat well, and recognize that where you carry fat makes a big difference.