Probiotic Relieves Anxiety in Chronic Fatigue Syndrome (Pilot Study)

Chronic Fatigue Syndrome (CFS) or Myalgic Encephalopathy (ME) is a complex illness of unknown cause that has both physical and psychological symptoms. The major physical symptom is intense bodily fatigue, which is made worse by bouts of physical or mental exertion and is not relieved by sleep. Muscle and joint pain and bowel conditions such IBS are often also seen. Psychologically, people with a diagnosis of CFS often report feeling depressed and/or anxious and find it hard to concentrate. Although it is not clear what causes CFS there is a strong link to increased markers of inflammation (the body’s immune response to illness or infection) and disturbances in the gut microbiome. This observation is interesting because the gut is the crucible of the immune system and plays an important role in ‘teaching’ the immune system to respond appropriately to pathogens and in distinguishing the body’s own cells from invaders.

In a small but well-designed pilot study, participants with a diagnosis of CFS and comorbid depression and/or anxiety were randomly assigned to two experimental groups. The test group took three sachets a day of a probiotic (Lactobacillus casei Shirota) totalling 24 billion bacteria per day. The control group ingested three sachets of an identical looking placebo product. After eight weeks the patients were reassessed on the depression and anxiety scales.

At the end of the test period not only had there been an increase in the number of Lactobacillus in the patients’ guts but also increased numbers of Bifidobacteria, a different strain of bacteria that is associated with a healthy digestive system. This is noteworthy a) because it indicates that the introduction of one helpful strain can encourage the proliferation of another, b) because CFS patients tend to have low levels of Bifidobateria and c) because some strains of Bifidobacteria are known to improve blood levels of tryptophan, an essential amino acid that is the precursor of serotonin, a neurotransmitter linked to happiness and good mood.

The researchers also found that patients who had been taking the probiotic were significantly less anxious than at the start of the study, a valuable finding considering the significant burden of anxiety in this patient group. Importantly, the probiotic was well tolerated, which means that it did not cause any unwanted or unpleasant side-effects.


Rao, A. V., Bested, A. C., Bealune, T. M., Katzman, M. A., Iorio, C., Berardi, J. M. & Logan, A. C. (2009). A randomized, double-blind, placebo-controlled pilot study of a probiotic in emotional symptoms of chronic fatigue syndrome. Gut Pathogens, 1:6.