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Where fat is distributed across the body—not merely the total amount—significantly and independently influences brain structure, brain function, and cognitive performance in middle-aged and older adults. This new study was published in Nature Mental Health.
Body mass index (BMI) has long served as the standard clinical and research measure of obesity, but it does not capture where fat accumulates in the body. Fat stored in different anatomical regions behaves in profoundly different ways biologically. Visceral fat—fat deposited around the internal organs—releases inflammatory chemicals linked to neuroinflammation and neurodegeneration. Limb fat, by contrast, has in some contexts been considered protective.
Despite this growing recognition, the vast majority of prior research on obesity and brain health has relied exclusively on BMI, leaving the distinct contributions of individual fat depots to brain aging and cognitive decline largely unknown.
Led by Anqi Qiu of The Hong Kong Polytechnic University, the team analyzed data from more than 18,000 UK Biobank participants (mean age approximately 62.5 years, ~45% male).
Fat in the arms, legs, trunk, and deep within the abdomen (visceral fat) was precisely measured using a specialized scanning technique (dual-energy X-ray absorptiometry, or DXA). Brain health was assessed using multiple types of MRI scans (structural MRI, resting-state functional MRI, and diffusion-weighted imaging), and participants completed a battery of cognitive tests covering reasoning, memory, executive function, and processing speed. Statistical methods were used to mathematically remove the influence of overall BMI so that the unique effects of each fat region could be examined independently of general obesity.
The results demonstrated that each fat depot was associated with distinct patterns of neurological change. Higher arm and trunk fat were particularly associated with thinning of the sensorimotor cortex, a brain region involved in movement and touch. Arm fat was also consistently associated with a reduction in the volume of the hippocampus, a key region for memory. All four fat types were linked to reductions in the volumes of deep brain structures, and all were associated with weaker connections between brain regions involved in movement and coordination.
Visceral fat—the fat that accumulates deep around abdominal organs—stood out as especially damaging. It was most strongly linked to deterioration in the brain’s white matter (the cables that connect different parts of the brain), showing signs of reduced nerve fiber density, increased fluid accumulation in brain tissue, and disorganization of nerve fibers.
Leg fat, interestingly, was uniquely associated with weakened connections within the brain’s limbic system, which governs emotion, memory, and reward. The authors suggest this may be related to the hormone leptin, which lower-body fat secretes at higher levels and which acts on memory-related brain regions.
The study used computer modeling to calculate a “Brain Age” for the participants’ neural networks. The researchers found that faster brain aging—particularly in the sensorimotor, limbic, and default mode networks—was the key pathway through which regional fat harmed cognitive performance.
Across all measures of thinking ability, visceral fat consistently showed the strongest negative indirect effects on cognitive function. As the authors stated, these findings “highlight the importance of considering regional adiposity, beyond BMI, in characterizing its associations with brain and cognitive aging.”
Several important limitations must be acknowledged. For example, the cross-sectional design cannot determine causality (if fat causes brain changes, or vice versa), and the predominantly white British sample limits generalizability to more diverse populations. Furthermore, the DXA scans lack the resolution to distinguish subcutaneous fat (just under the skin) from visceral fat specifically within the trunk region, which may have limited insights into their distinct effects.
The study, “Regional adiposity shapes brain and cognition in adults,” was authored by Die Zhang, Yingji Fu, Chenye Shen, Chaoqiang Liu, Nanguang Chen, Hua Cao, Kui Kai Lau, and Anqi Qiu.