Many by now will be familiar with the term ‘friendly bacteria’, referring to the vast population of bacteria in the digestive tract. This population of microbes (the microbiome) play an important role in maintaining our digestive health and many people consume yogurt and other fermented milk drinks to promote gut health. Increasingly research is showing us that the gut microbiome has a significant effect on our mental as well as physical health.

To gain a better overview of the current status of research in this area a systemic review of random controlled trials was conducted and published in the Journal of Neurogastroenterology & Motility. The researchers reviewed 25 animal and 15 human trials. Of the studies involving human participants just over half described significant effects of probiotics on central nervous system function and an intake of probiotics for four weeks appeared to be the threshold for noticeable effects. In the human trials the most common bacterial strains tested were Bifidobacterium longum, B. breve, B. infantis, Lactobacillus helveticus, L. rhamnosus, L. plantarum, and L. casei, all of which are present in fermented foods such as yogurt, kefir and traditional (unpasteurised) sauerkraut.

Looking at both the animal models and human trials the results of this review indicated that probiotics were an effective intervention for a range of mental health disorders including anxiety, depression, Obsessive Compulsive Disorder (OCD) and memory function. A number of potential mechanisms were identified:

Reduced cortisol (stress hormone) levels
Reduced inflammation.
Improved immune function

It is also feasible that some of the known metabolites of the microbiome such as GABA, an inhibitory neurotransmitter, might play a role either via the vagus nerve or more directly by crossing the blood-brain barrier. Whilst the review is generally positive the researchers called for further studies to be conducted with human participants in order to be able to draw firmer conclusions on the promising role of probiotics on mental diseases.

Reference:

Wang, H., Lee, I., Braun, C. & Enck, P. (2016). Effect of Probiotics on Central Nervous System Functions in Animals and Humans: A Systematic Review. Journal of Neurogastroenterology & Motility, 22, 589-605.

Just last week the NHS reported a study stating that there was insufficient evidence that probiotics were beneficial for healthy people. The trials analysed so far had not been well enough designed to be sure.

“Given the limitations of the studies – including the variety of probiotics examined – it is not possible to conclude with certainty that all probiotics are ineffective.

Absence of good-quality evidence is not evidence of there being no effect. Better-designed studies may yet find some benefit from taking probiotics.”

However, there is certainly some good evidence that particular probiotics do have a beneficial effect on depression, particularly where that depression is associated with cellular inflammation. Inflammation is the body’s immune response to illness or injury; the swelling around a cut or a bruise is part of this process. But inflammation also happens within and around the cell in response to other non-injury factors such as poor diet, prolonged stress or an imbalance of bacteria in the gut. Inflammatory diseases such as rheumatoid arthritis and inflammatory bowel disease are commonly associated with psychological and behavioural changes such as lack of energy or interest, loss of appetite, loss of appetite; and depression. This consistent relationship between inflammation and depression has led to the inflammation theory of depression; that is to say that for some sufferers inflammation may be contributing to the severity of their depressive symptoms.

A well-designed study of petrochemical workers published in 2015 showed that probiotic yogurt and supplements significantly improved scores of depression and anxiety. I have reported elsewhere that probiotics have been shown to alleviate the negative thoughts associated with low mood. A more recent controlled study showed that eight weeks of probiotic supplementation was associated with a significant reduction on depression scores in patients with a diagnosis of Major Depressive Disorder. It is thought that part of the mechanism underlying this effect are the by-products of the bacteria’s metabolism. When breaking down food in the gut (particularly fibre) gut bacteria produce a number of metabolites, many of them beneficial to the human body such as vitamin K and some B vitamins. They also produce short-chain fatty acids. One of these, butyric acid, in a potent anti-inflammatory. It also forms part of a neurotransmitter called GABA, which has a calming, tranquilizing effect on the brain.

There are a lot of probiotic products on the market and it can be difficult to know which is likely to be the most effective. There is very good research data supporting the anti-inflammatory properties of a highly concentrated probiotic supplement called VSL#3 in a number of different diseases. Whilst not necessarily a recommendation, this is the product that I use as well as ensuring regular consumption of fermented and high fibre foods.

http://www.nhs.uk/news/2016/05May/Pages/No-evidence-probiotics-are-beneficial-for-healthy-adults.aspx

Mohammadi, A. A., Jazayeri, S., Khosravi-Darani, K., Mohammadpour, N., Asemi, Z., Adab, Z., Djalali, M., Tehrai-Doost, M., Hosseini, M. & Eghtesadi, S. (2015). The effects of probiotics on mental health and hypothalamic–pituitary–adrenal axis: A randomized, double-blind, placebo-controlled trial in petrochemical workers. Nutritional Neuroscience. Published online April 16th.

Laura Steenbergen, Roberta Sellaro, Saskia van Hemert, Jos A. Bosch, and Lorenza S. Colzato. 2015. A randomized controlled trial to test the effect of multispecies probiotics on cognitive reactivity to sad mood. Brain, Behavior, and Immunity, 48, 258-264.

Akkasheh, G., Kashani-Poor, Z., Tajabadi-Ebrahimi, M., Jafari, P., Akbari, H., Taghizadeh, M., Memarzadeh, M. R., Asemi, Z., & Esmaillzadeh, A. (2016). Clinical and metabolic response to probiotic administration in patients with major depressive disorder: A randomized, double-blind, placebo-controlled trial. Nutrition, 32, 315-20.

D'Mello, C., Ronaghan, N., Zaheer, R., Dicay, M., Le, T., MacNaughton, W. K., Surrette, M. G. & Swain, M. G. (2015) Probiotics Improve Inflammation-Associated Sickness Behavior by Altering Communication between the Peripheral Immune System and the Brain. Journal of Neuroscience, 35, 10821-18030.

Mariman, R., Tielen, F., Koning, F. & Nagelkerken, L. (2014). The probiotic mixture VSL#3 dampens LPS-induced chemokine expression in human dendritic cells by inhibition of STAT-1 phosphorylation. PLoS One, 9: e11567.

Disclaimer

This information is provided for information purposes only and should not be taken as advice or instruction. This information does not replace the advice of your doctor. Please consult an appropriate health professional if you believe you are experiencing a mental or physical health concern. Speak to your GP or a trainer before making any significant changes to your exercise routine.