The Unexpected Connection Between Gut Bacteria and Depression and Anxiety

How depression and anxiety are connected to bacteria in the gut.

Consuming a prebiotic can have an anti-anxiety effect, the first ever human study of its kind has found.

Researchers at the University of Oxford have discovered that a prebiotic can reduce levels of anxiety in a clinical trial.

Like foods containing probiotic bacteria, prebiotics are functional foods: they have benefits beyond their purely nutritional value.

While prebiotics are non-digestible, they provide sustenance for healthy probiotic bacteria in the gut.

The study, published in the journal Psychopharmacology, involved 45 women taking either a prebiotic or a placebo for 3 weeks (Schmidt et al., 2014).

The results showed that compared with a control group, those taking the prebiotic had a reduced tendency to pay attention to negative information, which is a key component of anxiety and depression.

Women who took the prebiotic also had lower levels of the stress hormone cortisol, which has been connected to anxiety and depression.

The positive influence of the prebiotic was similar to that obtained by taking existing anti-depressant or anti-anxiety drugs.

Dr Phil Burnet, who led the study, said:

“The results of these trials add to the expanding body of knowledge on microbiome-behaviour and microbiome-endocrine interactions. The study makes an important contribution to the existing clinical evidence linking the gut and its microbiota to brain function.”

The gut-brain link

A previous study by researchers at UCLA was the first to find a link between human brain function and bacteria ingested in food (Tillisch et al., 2013).

Dr. Kirsten Tillisch, the first author of that study, said:

“Many of us have a container of yogurt in our refrigerator that we may eat for enjoyment, for calcium or because we think it might help our health in other ways. Our findings indicate that some of the contents of yogurt may actually change the way our brain responds to the environment. When we consider the implications of this work, the old sayings ‘you are what you eat’ and ‘gut feelings’ take on new meaning.”

Dr. Tillisch concluded:

“Time and time again, we hear from patients that they never felt depressed or anxious until they started experiencing problems with their gut. Our study shows that the gut-brain connection is a two-way street.”

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Image credit: Kevin Gebardt