Chronic Fatigue Syndrome (CFS) is a medically unexplained illness, characterized by persistent and relapsing fatigue [1, 2]. This severe pathological fatigue is worsened by periods of physical and mental exertion. Along with the ongoing fatigue, it has also been noted that 97% of CFS patients report neuropsychological disturbances. This can manifest as cognitive dysfunction, sleep disturbances, headaches, and a variety of symptoms in the emotional realm. Of these emotion-related symptoms, anxiety and depression are the most prevalent, with approximately half or patients meeting the criteria for an anxiety disorder or major depressive disorder. Over 40% of patients report symptoms that are often part of anxiety and depressive disorders, including dizziness, lightheadedness, heart palpitations, sleep disturbances, appetite changes and shortness of breath .
Many CFS patients also complain of gastrointestinal (GI) disturbances. Indeed, patients with CFS are more likely to report a previous diagnosis of irritable bowel syndrome (IBS), meet diagnostic criteria for IBS and experience IBS related symptoms . While CFS is neither a gastrointestinal nor psychiatric disorder per se, over 50 percent of patients with CFS meet the diagnostic criteria of IBS, and anxiety itself is often a hallmark symptom in those with IBS . Although the mechanisms behind this frequent overlap with IBS are far from understood, some investigators have documented that there are marked alterations in the intestinal microflora of CFS patients, with lower levels of Bifidobacteria and higher levels of aerobic bacteria .
Recently it was discovered that gut pathogens in the GI tract can communicate with the central nervous system and influence behavior associated with emotion, anxiety in particular, even at extremely low levels and in the absence of an immune response [7, 8]. Researchers have also shown that the administration of certain bacteria found in soil may support resilience and positively alter stress-related emotional behavior in animals under experimental stress . In addition, so-called probiotics, or live microorganisms which confer a health benefit on the host, have the potential to influence mood-regulating systemic inflammatory cytokines, decrease oxidative stress and improve nutritional status when orally consumed .
This background led some investigators to hypothesize a possible adjunctive therapeutic role of probiotic bacteria in mood-related psychiatric symptoms . Some hints at the utility of probiotics for mood regulation come from a recent human trial involving the administration of Lactobacillus casei strain Shirota (LcS) or placebo to 132 otherwise healthy adults. In an intriguing finding, the investigators discovered that those with the lowest scores in the depressed/elated dimension at baseline had significant improvement in mood scores after taking the probiotic compared to the placebo group. The probiotic bacteria and placebo were unable to make a difference in those with the highest baseline mood scores . In addition, ongoing experimental studies in this area have recently shown that in the animal model of depression, the oral administration of a probiotic can increase plasma tryptophan levels, decrease serotonin metabolite concentrations in the frontal cortext and dopamine metabolite concentrations in the amygdaloid cortex . With this background, the current investigation was initiated to determine if orally administered probiotics could make a difference in symptoms of depression and anxiety in adult patients with chronic fatigue syndrome.
Candidates for inclusion were screened from a pool of CFS patients in a tertiary setting. Those adult patients aged 18–65 meeting the formal diagnostic criteria for CFS, according to published guidelines,  were further screened for inclusion based on suitability to complete a two month trial. Excluded were those patients with unstable physical illness and those with a severity of CFS such that they were largely bedridden. Also excluded were patients meeting criteria for psychiatric disorders other than depression and/or anxiety. The study was approved by the institutional review board of the University of Toronto. Patients meeting inclusion criteria provided written, informed consent at the screening visit after the procedures had been fully explained.
CFS patients who met all inclusion/exclusion criteria were evaluated using the Beck Depression Inventory (BDI) and the Beck Anxiety Inventory (BAI). Patients also provided stool samples, taken over 3 days, at the evaluation phase. Kits were provided to the patients according to guidelines of appropriate collection as per the University of Toronto, School of Medicine, Department of Nutritional Sciences. Samples were sent to the Fecal Laboratory of the University of Toronto, Department of Nutrition for evaluation. Using culture technique, the stool samples were assessed for total aerobe, anaerobe, Lactobacillus spp, and Bifidobacteria spp counts.
After collection of the data and samples at the initial evaluation phase, 39 CFS patients were randomized to begin an intervention phase, an eight-week period where each patient consumed either a specific lactic acid probiotic bacteria or placebo by mouth. After each main meal, or three times daily, patients consumed the contents of an unmarked sachet containing 8 billion colony forming units (cfu) of Lactobacillus casei strain Shirota (LcS) or a placebo with identical taste and appearance. Each CFS patient in the active intervention group consumed a total of 24 billion cfu of LcS probiotic per day. Follow-up evaluation phase: After 8 weeks of intervention, LcS or placebo, subjects were re-evaluated by completion of the BDI and BAI, and a second stool analysis was conducted using the same collection and culture methods.
Thirty five CFS patients, 27 females and 8 males, completed the 8-week investigation. Four patients, two from the LcS probiotic group and two from the placebo group, withdrew from the study for reasons unrelated to the intervention. The LcS probiotic powder was well tolerated and there were no significant adverse events reported in the probiotic or placebo groups. Compared to the placebo control group, the treatment group showed moderate increases in fecal total aerobes and anaerobes and significant increases in fecal total Bifidobacteria and Lactobacillus (Figure 1). Among the Placebo group only 37.5% of subjects showed an increase in Bifidobacteria and 43.8% in Lactobacillus compared to 73.7% and 73.7% in the treatment group respectively (Table 1). The number of subjects showing changes in fecal Bifidobacteria and Lactobacillus is also presented in Table 2. An increase in the number of fecal Lactobacillus observed in this study was to be expected since the probiotic sachets contained high levels of a specific strain of this bacteria. The positive results observed with respect to Bifidobacteria are very encouraging since Bifidobacteria levels have been reported to be low in CFS, and they are generally associated with a healthy colonic environment. . It can therefore be concluded that ingestion of the probiotic capsules contributed towards the predominance of bacteria that are associated with a healthy gastrointestinal system.
When evaluating the BDI and BAI for changes over the course of the 8-week study, we found a statistical difference between the anxiety scores in those taking LcS or the placebo. Overall there was a significant improvement in anxiety among those taking the active LcS compared to the placebo (Table 3). The differences as assessed by the BDI did not reach statistical significance among those taking the active LcS.