Visceral fat and brain ageing: UK Biobank study in Nature Mental Health

You can match someone else on the scales, share the same BMI, and yet be living with a very different level of risk to your brain.

That is the takeaway from a growing body of research published over the last year.

Researchers have known for years that obesity is associated with a higher risk of dementia.

More recent evidence, however, suggests the story is not only about how much fat you carry, but where it sits on your body.

In May, one study connected visceral fat - the kind that accumulates around your organs - with more rapid brain ageing, pointing to glucose and insulin as likely mechanisms.

A new paper in Nature Mental Health, led by scientists at The Hong Kong Polytechnic University (PolyU), goes further.

What the UK Biobank study set out to test

Using the UK Biobank dataset, the team compared patterns of fat distribution with brain scans and cognitive scores from more than 18,000 people.

The researchers describe it as the world’s first large-scale multimodal analysis to systematically examine how fat location relates to brain structure, connectivity, and cognitive performance.

Their central finding is that fat placement is strongly linked to how quickly (or slowly) the brain appears to age.

"Fat in different parts of the body maps out entirely different trajectories of change in the brain, which cannot be detected by body weight or BMI alone," says PolyU neuroinformatician Anqi Qui.

"Our analytical model clearly demonstrates how fat in different regions causes differential damage to brain systems."

Fat stored in the arms, legs, trunk, and the visceral cavity each corresponded to different changes across distinct brain systems - including areas involved in movement, emotion, memory, and the brainstem.

In the figure below, you can see the brain areas associated with arm fat percentage (AFP), leg fat percentage (LFP), trunk fat percentage (TFP), and visceral adipose tissue (VAT).

That is obviously a lot for most of us to take in.

Visceral fat, white matter damage, and dementia risk

The key point, though, is that visceral fat was the only fat type directly associated with damage to the brain’s white matter - the connections that transmit signals between neurons.

White matter injury is closely linked to the biology underlying vascular cognitive impairment and cerebral small vessel disease - conditions that sit upstream of dementia risk.

The study did not test the cause of the relationship directly, but the authors suggest that long-term, low-grade inflammation associated with visceral fat could be affecting the brain itself, driving neuroinflammation.

"Visceral adipose tissue secretes pro-inflammatory factors … triggering systemic inflammation that contributes to neuroinflammation and white-matter damage," the team writes in their paper.

"In contrast, adiposity in the arms, trunk, and legs exhibits lower levels of inflammatory factor secretion."

This proposal is consistent with the insulin and glucose pathway highlighted by the group earlier this year.

What this could mean for health interventions

One encouraging implication is that overall body fat is something people can potentially change.

Even so, the research has clear limits. Although the sample was large, it remains an observational study and does not pinpoint direct causal drivers.

Much more research is still needed before we can fully unpack how this particular fat stored around organs relates to wider health. Even so, the direction of evidence is building.

"Regional adiposity is an intervenable and modifiable health risk factor," says Qiu.

"Reducing visceral fat through targeted lifestyle interventions can open up new pathways for the proactive prevention and treatment of neurodegenerative diseases."

The findings have been published in Nature Mental Health.

This article was fact-checked by Rebecca Dyer and edited by Rebecca Dyer. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.