Your brain and gut may have more in common than you realise. While scientists have long studied how gut bacteria influence digestion and immunity, new research suggests that these microorganisms could also provide clues about how quickly our brains are ageing.

A study conducted by researchers at the University of California, Los Angeles (UCLA), found connections between differences in gut bacteria, brain activity and cognitive performance.

Published in eBioMedicine in October 2026, the findings suggest that signs associated with brain ageing may appear decades before noticeable difficulties develop.

Can Your Brain Be Older Than You?

Chronological age tells us how many years someone has lived, but the brain does not necessarily age at the same pace.

Scientists can estimate its biological age by analysing patterns of communication between different brain regions. If these patterns resemble those typically found in older individuals, the brain may appear older than expected.

The UCLA team examined brain scans from nearly 1,500 adults across three independent groups. Using a computer model, they compared each participant's estimated brain age with their actual age.

The difference was measured using a tool called the Brain Aging Index.

What The Researchers Discovered

Participants whose brains appeared older than their chronological age generally performed less well on tests of working memory and executive function.

These abilities help us concentrate, organise information, make decisions and complete everyday tasks.

Researchers also found that higher brain ageing scores were associated with more symptoms of depression.

The patterns involved areas responsible for memory and self-referential thinking, suggesting that differences in brain function may be detectable even among relatively healthy adults.

The Surprising Role Of Gut Bacteria

For one group of participants, scientists also analysed stool samples to investigate the gut microbiome.

They discovered that older-looking brains were associated with particular bacterial profiles and changes in several chemical compounds produced or influenced by the body.

These included specific lipid molecules, a cholesterol-related compound and lower levels of the hormone estetrol.

The associated biological pathways involved immune responses, blood vessel function, energy production and communication between nerve cells.

However, the study did not establish that these bacteria directly accelerate brain ageing.

Can You Protect Your Brain?

Although the research opens interesting possibilities, it does not prove that probiotics, supplements or particular diets can reverse brain ageing.

The study was observational and assessed participants at one point in time, making it impossible to establish cause and effect.

For now, established healthy habits remain important. Regular physical activity, balanced nutrition, sufficient sleep and managing cardiovascular risk factors can support general health.

A New Direction For Research

The discovery highlights the complex relationship between the digestive system and the brain. Further studies could reveal whether changes in gut bacteria influence cognitive ageing or simply reflect other biological processes.

Understanding this connection may eventually provide new opportunities to protect brain health earlier in life.