How can gut bacteria help ease depressive symptoms?

Probiotics alone or combined with prebiotics may ease depressive symptoms, says study.

Depression is the second leading cause of disability worldwide, and researchers are busy looking for new ways to treat the condition. One area of interest is focusing on the gut-brain axis or the relationship between the digestive and nervous systems.

Although research is in its infancy, some evidence suggests the bacteria in our gut may not just support healthy digestion but could also benefit certain psychological conditions.

Sanjay Noonan and colleagues from the Brighton and Sussex Medical School in the UK reviewed seven articles published over 15 years, which found improvements in anxiety and depression in adults taking pre and probiotics compared to no treatment or placebo.

Probiotics increase the diversity of the bacteria in the digestive system. They are in supplements and fermented foods such as yoghurt, kefir, kimchi, sauerkraut, kombucha and fermented pickles. Prebiotics are compounds that help to keep gut bacteria healthy. Prebiotic foods include high fibre foods, onions, garlic, whole grains, bananas, beans and pulses.

Although the studies varied considerably in design, the British Journal of Medicine review concluded that probiotic supplements taken alone or combined with prebiotics helped ease symptoms and biochemical measures for depression. However, the findings for anxiety were less clear.

The author’s point out there is more to learn. For example, it was unclear how long any benefits may last; one study found that two months after stopping the supplementation, improvements in symptoms were lost. In addition, primarily Lactobacillus acidophilus, Lactobacillus casei, and Bifidobacterium bifidium were featured in the selected studies; however, there are many strains of probiotic bacteria, and it’s uncertain which ones help the most.

“Our results affirm that pre/probiotic therapy warrants further investigation. Efforts should aim to elucidate whether the perceived efficacy of pre/probiotic therapy in depression and/or anxiety disorders can be replicated in larger test populations, and whether such effects are maintained through continued treatment, or post cessation. Interventions should also be investigated in isolation, not combination, to ascertain where the observed effects are attributable to”, wrote the authors.


Noonan.S., Zaveri.M., Macaninch.E., Martyn.K. (2020). Food and mood: a review of supplementary prebiotic and probiotic interventions in the treatment of anxiety and depression in adults. BMJ, Nutrition Prevention and health 2020;

Accessed online 29th July 2020. Open access.

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