Microbiota and Your Mood

Microbiota and Your Mood

From the moment we are born, our body begins to house a unique and diverse population of microbes, commonly referred to as intestinal microbiota.1  While there are many factors that contribute to the colonization of these microbiota, one study suggests that the health of our microbes may be linked to our central nervous system2 and that consumption of a fermented milk product with probiotics could positively affect our emotional behavior and the way we interact with our surroundings.3 This also includes possible therapeutic treatments for gut and stress disorders. While the implications of these findings could be quite monumental, more research is necessary to confirm the potential benefits of these results.

In this study, found here, researchers created a single center, randomized, controlled, parallel-arm design in order to assess whether a 4-week trial of fermented milk product with probiotics (FMPP) could alter brain connectivity or responses to emotional tasks. The FMPP contained Bifidobacterium animalis, subspecies Lactis, Streptococcus thermophiles, Lactobacillus bulgaricus, and Lactococcus lactis: subspecies Lactis. With one intervention group (given the FMPP), and 2 control groups (one given a non-fermented control milk product, and one given no intervention), the study initially consisted of 36 women in total, with 12 in the intervention group, 11 in the first control group, and 13 in the second control group (with no intervention).  In order to measure their responses, the participants were given functional magnetic resonance imaging (fMRI) before and after the intervention to measure brain responses. Their stools were also analyzed pre- and post-intervention, along with their salivary estrogen and progesterone levels. With a P-value of .004, there was significant statistical difference in the regions of the brain responsible for central processing of emotion and sensation between the groups, signifying that probiotic ingestion was associated with altered brain connectivity.3

Overall, the study seemed to be constructed well, at least initially. Further reading revealed that 3 participants from the intervention group, and 6 from the control groups, were excluded because of different noncompliance issues, which means that the total sample size was actually 27, instead of 36. When compared to the rest of the female population, it’s a pretty small number to get quantifiable data from. Additionally, the mean BMI was 22.8, and according to the National Health and Nutrition Examination Survey put out by the Centers for Disease Control, the average American woman’s BMI is 28.7.5 Body weight composition will definitely be a factor in the effectiveness of different probiotic treatments, especially considering the differences in microbiota in overweight/obese people compared to people with leaner body weights.6 However, despite these issues, the study was executed well, and the results were measured accurately. In short, the study could have been a little more inclusive, but it was a good beginning with some interesting implications.

While it is clear that the study’s results weren’t all that extensive, there have been several other studies that have come to similar conclusions regarding the relationship between gut microbiota and the brain. In one double-blind, placebo-controlled, randomized study, found here, 66 healthy subjects were given a probiotic containing strains of bacteria related to the original study’s (Lactobacillus helveticus and Bifidobacterium longum) together for 30 days and then reevaluated. The chosen mediums were standardized questionnaires (Hopkins Symptoms Checklist and Hospital Anxiety and Depression Scale) that assessed anxiety, depression, stress, and coping mechanisms. The results found the probiotic treatment group to have significant improvement in all 4 categories, over the full 30 days, compared to the placebo group.7 This supports the conclusions found by the original study, further strengthening the idea that probiotics have beneficial effects on stress and other cognitive disturbances. Similarly, in another study of the same design, with 25 subjects, it was found that individuals who ingested a probiotic formula with the same type of bacteria (Lactobacillus helveticus and Bifidobacterium longum) showed improvements in several other categories besides the previous 4. Paranoid-ideation, anger-hostility, obsessive-compulsive, somatization, and GSI (global severity index test) all improved over a 30 day time period, in addition to anxiety, depression, perceived stress, and coping mechanisms.8 This expands further the possible implications of this research, lending additional support to probiotics’ role in emotional behavior and influence. Additionally, in another double-blind, randomized, placebo-controlled study, 39 patients reporting high-anxiety levels due to chronic fatigue syndrome (CFS) were given a probiotic containing Lactobacillus casei strain Shirota for 8 weeks. After the intervention period, it was found that there was significant improvement in anxiety scores in those taking the probiotic versus the placebo group.9 While this study is labeled as a pilot, the results were still conclusive and in agreement with the original study, and thus worth reporting. Furthermore, in another study of the same design, 124 patients were given a probiotic containing the same live bacteria as in the previous study (Lactobacillus casei strain Shirota) for 20 days, assessed at Day 1, 10, and 20. It was found that those who were more depressed at Day 1 showed significant improvement in overall mood and mood outlook after the full 20 days of consumption.10 While this study is relatively older research, its importance is reflected in its comparatively larger sample size relative to the other studies. Indeed, it may be the largest clinical study conducted about this topic, as no other study of greater than or equal magnitude could be found. As is evident by the results from each study, probiotics definitely seem to have an impact on emotional behavior via gut microbiota manipulation. Each study exhibited positive changes to emotional response, especially in regards to stress and anxiety, purportedly due to consumption of different probiotic supplements. While more research is necessary, these findings present new ideas for progress that would be worth exploring.

Overall, this study did a great job of introducing a new way of thinking about how our bodies communicate. The idea that probiotics could influence our emotional behavior in a positive way is a novelty in its own right, and is something that has just recently come into focus for many scientific circles. This means that in the future, there will be more research available, but right now, the information is lacking. It became increasingly obvious that this was among the few noteworthy clinical studies regarding this topic, the rest of which have been mentioned above. Unfortunately, the majority of research on this is all preclinical, leaving plenty of room for additional research in the future. Hopefully, this subject will peak the interest of other researchers soon, as it has some very interesting psychological implications.



  1. Dogra S, Sakwinska O, Soh S, Ngom-Bru C, Brück WM, Berger B, Brüssow H, Lee YS, Yap F, Chong Y, Godfrey KM, Holbrook JD. 2015. Dynamics of infant gut microbiota
    are influenced by delivery mode and gestational duration and are associated with subsequent adiposity. mBio 6(1):e02419-14. doi:10.1128/mBio.02419-14
  2. Foster JA, Mcvey neufeld KA. Gut-brain axis: how the microbiome influences anxiety and depression. Trends Neurosci. 2013;36(5):305-12.
  3. Tillisch K, Labus J, Kilpatrick L, et al. Consumption of fermented milk product with probiotic modulates brain activity. Gastroenterology. 2013;144(7):1394-401, 1401.e1-4.
  4. Wang Y, Kasper LH. The role of microbiome in central nervous system disorders. Brain Behav Immun. 2014;38:1-12.
  5. Available at: http://www.cdc.gov/nchs/data/nhanes/databriefs/adultweight. Accessed February 5, 2015.
  6. Moloney RD, Desbonnet L, Clarke G, Dinan TG, Cryan JF. The microbiome: stress, health and disease. Mamm Genome. 2014;25(1-2):49-74.
  7. Messaoudi M, Lalonde R, Violle N, et al. Assessment of psychotropic-like properties of a probiotic formulation (Lactobacillus helveticus R0052 and Bifidobacterium longum R0175) in rats and human subjects. Br J Nutr. 2011;105(5):755-64.
  8. Messaoudi M, Violle N, Bisson JF, Desor D, Javelot H, Rougeot C. Beneficial psychological effects of a probiotic formulation (Lactobacillus helveticus R0052 and Bifidobacterium longum R0175) in healthy human volunteers. Gut Microbes. 2011;2(4):256-61.
  9. Rao AV, Bested AC, Beaulne TM, et al. A randomized, double-blind, placebo-controlled pilot study of a probiotic in emotional symptoms of chronic fatigue syndrome. Gut Pathog. 2009;1(1):6.
  10. Benton D, Williams C, Brown A. Impact of consuming a milk drink containing a probiotic on mood and cognition. Eur J Clin Nutr. 2007;61(3):355-61.

Reviewed by Viktoriya Wolff

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