What if a stool sample from a two-year-old could hint at a child's mental health five years later? It sounds like science fiction, but a study from Singapore suggests exactly that.
From Gut to Brain
Researchers at UCLA used data from the GUSTO study — a large birth cohort in Singapore that follows children from birth through school age. They examined stool samples from 55 children at age 2, brain scans at age 6, and questionnaires about behavioral problems at age 7.5.
The results, published in Nature Communications in October 2025, were striking: children who at age 2 had higher levels of certain bacteria in the Clostridiales order and the Lachnospiraceae family showed altered brain connectivity in emotion-related networks at age 6 — and a higher risk of anxiety and depression symptoms at age 7.5.
A Cascade Effect
The connection appears to work indirectly: gut bacteria shape brain networks, which in turn influence emotional health. The researchers note that the same bacterial groups have previously been linked to stress responses and depression in adults, as well as to the effects of early childhood stress.
"By linking early gut microbiome patterns with brain connectivity and later symptoms, our study provides early evidence that gut microbes may help shape mental health during the critical school-age years," says lead researcher Bridget Callaghan at UCLA.
No Cause for Panic
It's important to emphasize that this is an observational study with a limited sample size. Researchers do not yet know whether the association is causal — that is, whether the gut bacteria actually cause the changes, or are simply a marker. Future research aims to clarify this, and potentially to examine whether probiotics or dietary changes could make a difference.
What This Means for Parents
The WHO and AAP recommend breastfeeding and a varied diet to support gut health in infants and young children. Pediatricians monitor children's development at regular well-child visits, including aspects of mental and behavioral health. You can read more about your baby's immune system and gut flora in infants in our articles.