While we’ve known for some time that obesity affects the brain, scientists have found that, more importantly, it’s where you carry it that matters. And it’s the deep visceral fat around organs that has the biggest impact on aging your brain, affecting areas of reasoning, memory and processing speed.
Researchers from The Hong Kong Polytechnic University (PolyU) have used a massive UK Biobank dataset analysis to identify that fat distribution, not just overall size, maps to distinct changes in brain structure and connectivity. And visceral fat stands out as the strongest red flag, linked to poorer reasoning, memory and processing speed. It adds more evidence to the need to do away with the body mass index (BMI) – judging weight and height alone – as an accurate marker of brain health (and health more broadly).
The team gathered regional body-fat measurements, via dual-energy X-ray absorptiometry (DXA) scans, and a combination of MRI scans covering structure, network activity (resting-state fMRI) and white-matter wiring (diffusion), from the UK Biobank. The scientists analyzed the data of 23,088 people who had DXA scans of their arms, legs and trunk fat, as well as a smaller subset of 18,886 participants who also had visceral fat measurements taken. Everyone in both groups had the three MRI scans, and those were used to correlate with the fat measures.
The team found that fat location maps to different brain changes. More fat on the arms, legs and trunk was linked to a thinner cortex in the brain’s default-mode and limbic networks – systems that support memory, internal focus and emotional regulation – pointing to slightly less efficient recall and mood control. Visceral (deep abdominal) fat showed additional hits, associated with shrinkage in the medial prefrontal cortex, which underpins planning, judgment and impulse control, and in smaller subcortical structures involved in habit learning, reward and movement.
Beyond anatomy, when researchers looked at how brain regions naturally coordinate over time, people with more fat – and most clearly those with higher visceral fat levels – showed subtly retuned coordination within networks that drive movement and touch, mood and motivation, memory and mind-wandering, and alertness and reflexes. And in the brain’s white-matter wiring, visceral fat again stood out, with diffusion MRI scans revealing lower axon density and more tissue disorganization – tiny areas of wear-and-tear that can interrupt signaling.
The researchers conclude that regional fat distribution has varied effects on brain and cognitive aging, completely independent of BMI. And visceral fat appears to play a more significant role in neurocognitive changes.
So what exactly is visceral fat? Unlike subcutaneous fat – the layer of “soft” fat under the skin that makes up around 90% of our adipose tissue – visceral fat is the layer deep inside the abdomen surrounding organs like the liver, kidney, pancreas and intestines. It behaves like an endocrine organ, releasing inflammatory chemicals and free fatty acids straight into the liver via the portal vein. That drives insulin resistance, fatty liver and undesirable blood lipids, raises blood pressure and cardiovascular risk, and is linked to sleep apnea. It’s also been implicated in the early development of Alzheimer’s disease.
While we all have visceral fat, fatty foods and carbohydrates (sugars) can contribute to higher amounts of it being stored if physical activity is low. What’s more, the stress-triggered hormone cortisol can add to the amount of fat that gets stored away. While it’s hard to target, visceral fat area can be reduced through the usual methods – diet, aerobic exercise and weight training, as well as maintaining good sleep health and combating stress levels.
It’s worth keeping in mind that the changes in the brain, the researchers noted, are modest but meaningful. Overall, though, it shows that being obese or having a high BMI is not indicative of brain aging, but more so how different regions of fat – particularly deep belly fat – align with alterations in different areas of the brain and in turn impact different cognitive functions.
The research has its limitations – it’s a population-level, cross-sectional study, not a causal trial. And while the scientists adjusted for age, sex, education, lifestyle factors and metabolic syndrome, and made use of multiple-comparison controls across several modes of imaging, more work is needed to unravel the long-term impacts of regional fat on brain aging and cognition, and if reducing visceral fat, especially, could change those brain biomarkers.
“This study provides a comprehensive framework to delineate the differential relationships between regional adiposity and the selective vulnerability of brain systems and cognitive function,” the researchers noted. “By integrating multimodal brain imaging with regional adiposity measures, our work offers a novel perspective on the link between regional adiposity and obesity-related brain alterations, although the effect sizes are modest. It also underscores the heterogeneous nature of the brain–fat connection and the potential role of regional adiposity, particularly visceral adiposity, in shaping trajectories of brain and cognitive aging.”
It also adds to a growing body of evidence supporting the need to move beyond BMI in predicting health and disease risks.
“Together, this work strengthens the rationale for incorporating regional adiposity into future neuro-epidemiological research and highlights its potential to inform strategies preserving brain health,” they added. “Longitudinal and interventional studies are warranted to further evaluate the predictive utility of these markers and their relevance to trajectories of neurocognitive aging.”
The research was published in the journal Nature Mental Health.
Source: The Hong Kong Polytechnic University via MedicalXpress
