Babies, Anxiety and the Gut Biome

Remember last Thursday, when I wrote about the relationship of the gut bacteria to the structure and function of the brain?    I mentioned in that post that, “In Western populations, Bacteroides and Prevotella species tend to dominate, with the former outnumbering the latter –as they did in this sample of women. A diet high in fat and animal protein (i.e. a standard Western diet) is more associated with higher Bacteroides species than Prevotella…”  I went on to point out that, “Prevotella levels are markedly higher in non-Westernized societies, which consume plant-based diets, where people are actually less prone to ‘mental’ illnesses like depression or anxiety. And don’t forget, low levels of Prevotella  have also been associated with leaky gut and also, Parkinson’s disease.  So the likelihood is that higher Prevotella amounts are better for health.”

With that fresh in mind, yesterday morning I spotted an article[i] that looked at the composition of the bacterial microbiome in infancy and its relationship to the development of anxiety issues in toddlers, and the findings should come as no surprise:  “…we found a clear association between decreased normalised abundance of Prevotella in faecal samples collected at 12 months of age and increased behavioural problems at 2 years…”

This finding held even when other variables were accounted for, like mode of birth, pet ownership, maternal smoking, breast feeding, and so forth.

The test group tested consisted of 201 infants, selected from an Australian birth cohort of over 1000 babies.  Stool samples were collected at 1, 6 and 12 months, and when the babies reached 2 years of age, their parents filled out extensive questionnaires.  No association was found in behavioral differences based upon the first 2 stool collections, but the 12-month sample found significant associations.  Believe it or not, Prevotella was found in only 4% of the children who went on to have anxiety issues versus 44% of the children without any problems.  (Lacnospiraceae species were also altered in the behavior group, although when other factors as mentioned above were accounted for, this was somewhat less significant.)

The main factor leading to lower levels of Prevotella? You guessed it: antibiotic use.  However, the behavior group’s antibiotic use was not different from the non-behavioral group with low levels of Prevotella, so this was not considered significant in terms of predicting behavior.

The mechanisms are still unknown but there are numerous possibilities:  stimulation of the vagus nerve, various enzymes or cytokines, tryptophan metabolism, the immune system, and so forth.  Studies are already underway to replicate these findings and to delve into causality.  The implications of this work may be huge:  as these authors state, this work “…adds support to evidence that the human gut microbiota may have long-term neurodevelopmental consequences, conferring protection or vulnerability to behavioural and mental health outcomes in later life…”  This work, therefore, may have tremendous relevance not only to anxiety disorders (which are on the increase in industrialized nations) and other mental health issues, but also autism (remember the fecal microbiota transplant study – FMT led to higher levels of good bacteria, including Prevotella, which is low in those with autism), and potentially illnesses that tend to hit in later life, like Parkinson’s disease.  It’s looking more and more like eating right from the moment of birth is crucial for long-term physical and mental health.

Hopefully there will be more to report to you in the near future.  In the meantime, eat that plant-based diet!


[i] Loughman, A, et. al. Gut microbiotia composition during infancy and subsequent behavioural outcomes. EBioMedicine. 2020. DOI:

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