Can Probiotics Improve Your Mood?

While there is a wealth of evidence connecting the gut microbiome and mood, there is less quality evidence to suggest that probiotics are a useful tool to actually modulate mood.

The gut and brain are known to be connected via a signalling system called the gut-brain axis. Alterations in the microbiome can change the signalling to the brain and vice-versa. A recent systematic review found that probiotics may be a useful adjunctive treatment for depression and anxiety, however another similar review had the opposite finding. There is no evidence to suggest probiotics have a positive effect on mood in people without cognitive.

The wide applicability of results in this field are limited due to small studies, a lack of long-term follow up and a lack of mechanistic insights. Additionally, as different studies use different types of probiotics, it is difficult to generate a broad understanding of what effects probiotics have on gut-brain axis signalling.

Probiotics are often made of specific strains of bacteria, which in contrast to faecal transplants, do not contain the broad diversity and inclusion of bacterial metabolites. This may therefore reduce the effectiveness of a probiotic on changing microbiome composition.

More research is required to fully understand how to best modulate the microbiome in a way that could improve mood.

There are certainly studies that show associations between the type of bacteria in our guts and brain function. For example, people with depression have distinct microbial traits compared to people without depression. Similarly, in people who have had chemotherapy for cancer, the degree of microbial injury is also associated with psychoneurological symptoms. But, associations do not mean causation! In other words just because two things occur at the same time, they are not necessarily linked in a causal manner.

This is a very big challenge in the microbiome field because when we look at a cross section of people with a certain disease, we dont know if the disease caused the changes in the microbiome, or the microbiome caused the disease…. just like the chicken or the egg. In reality, it is likely that the communication between the gut and the brain is bidirectional.

Take for example when we get nervous or stressed…. many of us need often need to use the loo. Similarly, people with gastrointestinal diseases like inflammatory bowel disease, often show a higher incidence of psychological disturbance. Nonetheless, it is near to certain that the gut and brain are inexplicably linked, and the microbiota is likely to be involved in this process.

In terms of probiotics and brain function, it remains unclear. If discussing “healthy” people, there is no robust evidence to suggest that probiotics have no appreciable benefits in gut health, immune function or brain function. Often, adopting a healthy diet and exercising is more effective. In people with psychological symptoms, such a depression, it also remains unclear. A recent meta-analysis (a large study of already published data), showed that probiotics were unable to have any benefit for people with depression. However, when administered in conjunction with antidepressants they were shown to provide additional benefits. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6595633/

However, there is also conflicting data: https://pubmed.ncbi.nlm.nih.gov/29197739/ – this meta analysis showed benefits of probiotics in promoting mood.

So – the jury is out! It is also important to note that probiotics are increasing considered sub-par, with many being limited in the number of diversity of bacteria that they have – this is why they have such variable results in the literature. More recently, the use of faecal transplants has been suggested for depression management. Faecal transplants have a much higher density and diversity of bacteria as well as all of their metabolites (which have benefits of their own that bacteria cannot achieve alone). There is currently a trial being conducted on this topic https://pubmed.ncbi.nlm.nih.gov/29197739/ , so watch this space!