Brain scans from nearly 1,500 adults sorted people by an index of how old their brains looked relative to their calendar age, and in one of the three groups scanned, a higher index lined up with a distinct set of gut bacteria and the chemicals those bacteria help produce. Dr. Arpana Church, co-director of the Goodman-Luskin Microbiome Center at UCLA Health, is senior author of the work in eBioMedicine. UCLA’s announcement came on September 10, 2026.
People with older-looking brains also tested worse. Higher scores on the Brain Aging Index went with weaker working memory and executive function and with more depressive symptoms, and the pattern held in regions tied to memory. The index is a gap: estimated brain age minus chronological age, so a positive number means a brain that behaves older than its owner.
Building the Brain Aging Index from resting scans
UCLA’s release describes a resting-state design: participants lay in a scanner doing nothing in particular while imaging captured how regions of the brain communicate with one another. A statistical model trained on those connectivity patterns estimated each person’s brain age. A write-up on mindbodygreen reports the brain was divided into 100 regions for the model.
First author on the paper is Kanhao Zhao, with Gabriel A. Vignolle and Jennifer S. Labus among the co-authors, according to SciTechDaily’s account, which also lists the National Institutes of Health as the funder. Most earlier brain-age work examined older adults or people with established brain disease. This analysis drew on younger and middle-aged adults who were generally healthy, which is why Church frames it around detection long before symptoms. In her words, brain aging does not suddenly begin in later life, and its biological signals may be detectable decades earlier.
Bacteria and byproducts in one of three cohorts
The gut portion of the study is smaller than the brain portion. Only one of the three groups provided stool samples, according to the Newswise copy of the release, so the bacterial link rests on that group alone rather than the full 1,500. In it, a higher Brain Aging Index tracked with particular gut bacteria and with metabolites: certain fat molecules, a cholesterol-related compound, and lower levels of the hormone estetrol. The mindbodygreen write-up names ceramides and dicarboxylic acids among the metabolites and identifies the cholesterol-related compound as 24-hydroxycholesterol.
None of the public coverage names the bacteria themselves. UCLA’s announcement and every summary of it say “specific gut bacteria” or “microbial taxa” without a genus or species, so the exact organisms are not identified outside the journal paper. Readers looking for a probiotic or a food to target will not find one in what UCLA has said.
The size of the sample behind each claim differs, and the pairing of specific bacteria with faster brain aging draws on the smaller piece of the dataset, the one cohort that supplied stool samples. The brain-scan results, covering memory, executive function and depressive symptoms, rest on all of the roughly 1,500 adults. The microbiome results rest on one cohort. Secondary summaries disagree on that cohort’s exact size, with one reporting 344 people with stool samples against 674 scanned, and UCLA’s release states only the combined figure, so the cohort-level counts are best read from the eBioMedicine paper itself, listed as volume 132, article 106468.
Immunity, blood vessels and association, not cause
The metabolites point toward four biological systems, according to Med Bound Times: immune function, vascular health, communication between neurons and cellular energy metabolism. Those are the pathways UCLA describes as implicated, which makes them candidate routes by which gut-derived chemicals might reach the brain rather than demonstrated ones, since a correlation between a blood or stool signature and a scan cannot show a chemical crossing from gut to brain.
The design is observational. Mindbodygreen states the limit directly: the work does not show that an older-looking brain causes cognitive problems or depression, nor that gut bacteria drive brain aging; it cannot establish which comes first or whether a third factor sits behind both. A single cohort’s stool samples taken alongside a scan cannot separate a microbiome that ages the brain from a brain whose aging alters behavior and, through it, the microbiome.
Church’s own wording stays at the level of the data. Church said that linking these early brain changes with the gut microbiome and its metabolites begins to identify pathways that could ultimately clarify who may be at risk, according to Med Bound Times. The statement is about identification, not treatment: no intervention was tested, and no participant was asked to change their gut flora. A reprint dated October 4 carries the same UCLA wording and the same gap: the bacterial names remain unpublished in it.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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