An analysis of MRI scans shows that a lower accumulation of abdominal fat in midlife is associated with a significant slowing of brain atrophy (shrinkage), preservation of key brain structures, and better cognitive performance in late midlife -- independent of weight loss.

Magnetic resonance imaging (MRI) scans of the brain and abdomen were analysed of 533 women and men in late midlife, who were followed for up to 16 years. During this period, participants underwent repeated MRI measurements of visceral fat and brain structures, along with their cognitive assessment.

The findings, published in the journal Nature Communications, suggest that the relationship between abdominal fat and brain ageing is likely brought about primarily through glucose control and insulin sensitivity.

Researchers, including those from the Ben-Gurion University of the Negev, Beer-Sheva in Israel and Harvard T. H. Chan School of Public Health in the US, said the study is the first to link repeated MRI-based measurements of cumulative visceral fat with long-term trajectories of brain aging and cognition.

Lead researcher Iris Shai, from Ben-Gurion University of the Negev, said, "The findings point to glucose control and reduction of visceral abdominal fat as measurable, modifiable, and achievable targets in midlife -- with real potential to slow brain degeneration and reduce the risk of cognitive decline."

In a subgroup of participants, three brain MRI scans were taken over five years, analysis of which showed that persistently elevated levels of visceral fat over time were associated with a faster rate of brain volume loss, particularly in the hippocampus (brain's memory centre), and with accelerated enlargement of the brain ventricles.

The links were not observed for subcutaneous fat, either superficial or deep, nor for body mass index (BMI), highlighting the biological specificity of visceral fat, the researchers said.

The study "suggests that sustained visceral fat loss, rather than weight loss, is linked to better cognition and attenuation of brain atrophy years later, mainly via improved glycemic control".

"Improved glycemic control parameters, rather than lipid or inflammatory markers, were mostly related to the favourable longitudinal brain outcomes," the authors wrote.

Reductions in visceral (abdominal) fat during an 18-month dietary intervention predicted a better preservation of brain structures five and 10 years later, even after accounting for weight loss and other factors.

In other words, the reduction in abdominal fat itself -- rather than weight loss per se -- was the factor predicting long-term brain outcomes, the researchers said.

The association between visceral fat and brain aging was found to be mediated primarily through glycaemic balance.

Fasting glucose and HbA1c levels were the only markers that predicted the rate of structural brain change over time, whereas blood lipid markers or inflammatory markers did not show a similar association.

The findings support the hypothesis that insulin resistance and chronic dysregulation of glucose metabolism impair cerebral perfusion, compromise blood-brain barrier integrity and accelerate degeneration of gray matter and the hippocampus, the researchers said.