Do psychobiotics work?

Hello everybody. In the previous videos and articles we’ve seen that there is a link between our gut and our brain – more importantly, we have seen that there is a link between our gut microbiome and our health, both psychological and physical. One approach used to verify these connections is to modify the microbiome, observe the changes that follow the intervention and to draw a connection between the cause and the results obtained. Of course, when scientists observe positive effects, the next step is to try to translate the results obtained in animal models, or in cell cultures, to humans. Broadly speaking, there are two classes of foods and supplements that are sold for they

beneficial effect on our gut bacteria: probiotics, which we already discussed, and prebiotics. Prebiotics are substances that encourage the growth and the activity of beneficial organisms, and is usually used when talking about compounds that affect the gut microbiome. We discussed one study showing the effects of prebiotics on the human brain in the last video, but is there more evidence that modifying the microbiome, using either approach, can improve our mental health? Well, most studies actually assessed the effects of pro and prebiotics on digestive system disorders, or on allergic syndromes, and they found positive effects on some forms of diarrhea or on the symptoms of irritable bowel syndrome.

A few studies, however, tried to replicate in humans the studies investigating the neural and psychological effects of probiotics on mice. As the enthusiasm for this new field started to grow, a new word was coined to indicate those probiotics that could have

positive effects on our mood and cognition: psychobiotics. In one study investigating psychobiotics, researchers recruited 55 healthy volunteers for a clinical trial, giving half of them a placebo and half of them a specific probiotic formulation. This study found a positive effect of the probiotic formulation in anxiety, depression and other symptoms of psychological distress after one month of treatment. Two years before, another study investigated the effect of a prebiotics whose name you might recognize – lactobacillus casei shirota – on the depressive and anxious symptoms of patients suffering from chronic fatigue syndrome.

This study, too, found a significant decrease of anxiety symptoms in patients that took the probiotic, as well as an increase of the number of ‘good’ strains of bacteria in their digestive systems. There are other, more recent clinical studies But if we just look for studies that have published in scientific journals, we run into the risk of only seeing what works, and not what does not work – studies that find nothing usually don’t get published!

So, we can try another approach: clinical trials – the more rigorous experiments to assess whether a treatment has a significant effect or not – are often registered on databases even before they start. It is then easy to see which ones have been discontinued, which ones have been completed and what are the results. As of mid 2019, there are 10 active clinical trials that investigate probiotics or prebiotics in the treatment of depression, five that investigate the treatment of anxiety, two that focus on the treatment of obsessive- compulsive disorders, and at least two that deal with cognitive impairment.

To put these numbers into scale, at the moment there are about 300 active trials investigating pre or probiotic, and more than 1000 trials on depression. It seems then that while psychobiotics are a small, but not insignificant, part of the probiotic trials, they are only a tiny percentage of the broader field of the studies assessing new treatments for psychological illnesses. An intermediate, and very important, stop on the road to understanding whether psychobiotics are effective is to understand their possible mechanisms of action. As of today, it is still unclear, but given their effects on asthma, eczema and other allergic symptoms, it is possible that the immune system plays a role in the interaction between the microbiome and the brain.

This would bring us back to our lecture on inflammaging, and it would be another step into painting a big picture that puts together our gut, the food we eat and their consequences on our body and on our mind.