The pace of brain aging may be connected to bacteria in the gut. A new UCLA study offers an early look at biological changes that begin long before memory problems appear.

The findings were published in the journal eBioMedicine. Researchers examined brain scans from nearly 1,500 adults across three separate groups.

The team measured how different brain regions communicate at rest. A computer model estimated each person’s age from those patterns. The gap between the estimated age and the real age became the Brain Aging Index.

Across all three groups, people whose brains looked older than their age scored worse on tests of working memory and executive function. They also reported more symptoms of depression.

In one group, the researchers also examined stool samples. A higher Brain Aging Index was linked to specific gut bacteria and metabolic byproducts, including certain fat molecules and lower levels of a hormone called estetrol.

Senior author Dr. Arpana Church said brain aging does not suddenly begin in old age. Its signals may be detectable decades earlier. Targeting gut health could one day support healthier brain aging.