Although probiotics have been reported to improve symptoms of irritable bowel syndrome (IBS), data in humans regarding their effects on psychiatric comorbidities is scarce.

A new study, led by Prof. Premysl Bercik from the Department of Medicine at the Farncombe Family Digestive Health Research Institute at the McMaster University in Hamilton (Canada), has found that the probiotic Bifidobacterium longum NCC3001 can reduce depression scores and increase quality of life in patients with IBS.

The researchers performed a randomized, double-blind, placebo-controlled study of 44 adults with IBS and diarrhoea or a mixed-stool pattern (according to Rome III criteria) and mild to moderate anxiety and/or depression scores based on the Hospital Anxiety and Depression (HAD) scale (HAD-A or HAD-D score 8-14). Patients were randomly assigned to the probiotic group (B. longum NCC3001 1.0 x 10^10 colony-forming units/gram powder with maltodextrin every day; n = 22) or the placebo group (1 gram of maltodextrin every day; n = 22) for 6 weeks. At weeks 0 and 6, patients’ levels of anxiety and depression (primary outcome), IBS symptoms, quality of life and somatization (using a validated questionnaire), stool, urine, and blood samples were collected, together with an assessment of changes in brain activation patterns (using functional Magnetic Resonance Imaging, fMRI). At week 10, patients’ levels of anxiety and depression, IBS symptoms, quality of life, and somatization were also determined.

Both the intervention and placebo groups had similar faecal microbiota profiles, serum markers of inflammation, and levels of neurotrophins and neurotransmitters. However, the probiotic group had reduced urine levels of the metabolites methylamines and aromatic amino acids.

Although the probiotic had no effects on anxiety or IBS symptoms, it led to a significant reduction in depression scores of 2 points or more on the HAD scale in 14/22 patients. It was also shown that the beneficial effects of the probiotic on depression scores at 6 and 10 weeks was more likely to occur in those patients who reported adequate relief of IBS symptoms. Besides this, the probiotic also led to an increase in quality of life score (measured by the SF-36 questionnaire) compared with the placebo group. At week 10, depression scores were also reduced in patients given the probiotic versus the placebo.

Regarding brain activation patterns assessed by fMRI, the probiotic reduced responses to negative emotional stimuli in the amygdala and fronto-limbic regions, as compared with placebo. In the intervention group, reduced engagement of the amygdala correlated with decreased depression scores and was more likely to occur in those patients with adequate relief of IBS symptoms.

In conclusion, 6-week administration of Bifidobacterium longum NCC3001 decreased depression scores and decreased brain activity in areas involved in the processing of negative emotions. Besides this, the probiotic also improved overall symptoms of IBS and quality of life. According the authors, “This is the first study to show that probiotics can improve depression scores as well as alter brain activity patterns in IBS patients with comorbid depression and anxiety”.




Pinto-Sanchez MI, Hall GB, Ghajar K, et al. Probiotic Bifidobacterium longum NCC3001 reduces depression scores and alters brain activity: a pilot study in patients with irritable bowel syndrome. Gastroenterology. 2017. doi: 10.1053/j.gastro.2017.05.003.