Straight from the gut

You’ve probably heard the expression “going with your gut”. This essentially means you have an instinctive feeling about something that’s not necessarily based on evidence or fact - you just know - and you decide to act accordingly. Indeed, our stomachs are privy to reacting when we find something distressing or exciting. Perhaps you’ve experienced nausea when you’re about to give a presentation, or needing to go to the bathroom more frequently before a first date. But are we right in trusting our gut, and should we, really, go with it?

The answer may be yes. Our brains and our guts do continuously communicate in a bidirectional way. This connection is known as the gut-brain axis. Our brain and gut contain neurons which are cells that tell your body how to behave. The neurons in our guts and our brains communicate through various nerves, the biggest of which is known as the vagus nerve. If the signals sent through the vagus nerve are inhibited, or made weaker, this can cause physical symptoms such as gastro-intenstal problems which can be linked to anxiety (Liu & Zhu, 2018). In this way, our heads and stomachs are in constant communication and may actually inform one another when it comes to decision making.

This leads us to ask, can that feeling in our stomachs tell us anything about our mental health? There is a growing interest in how the presence of certain bacteria in our stomachs affects our mental health in the scientific community, and a lot of research is being carried out into just how these bacteria impact the communication between gut and brain. The bacteria of interest are known as gastrointestinal microbiota in our stomachs. These gastrointestinal microbiota (microbiota from hereon) are a collection of bacteria, yeasts, and fungi in our gastro-intenstinal tracts. Their presence, or lack thereof, has been linked to a variety of health outcomes such as type 2 diabetes and colon cancer (Gomes et al., 2014).

More recently, researchers have started finding links between microbiota, their impact on gut health, and how this in turn affects mental health. The communication between microbiota and the central nervous system (which controls most functions of body and mind) occurs through a number of pathways. If this communication is disrupted or altered, it can have an adverse impact on our mental health (Rieder et al., 2017). Furthermore, the bacteria found in our intestines can also produce chemicals that impact our functioning, for instance melatonin (connected to our sleep-wake cycle) and serotonin (related to a range of functions). So, sometimes that bad feeling you have in your stomach may be a disruption to the communication between the gut and the brain - thus, maybe not always reliable as a decision-maker.

Probiotics are a type of live bacteria that are thought to help restore the natural balance of bacteria in your gut and thus aid in keeping the communication between gut and brain effective, as well as the production of beneficial chemicals. Researchers are investigating if this could help reduce depressive symptoms. In their 2017 study, Pinto-Sanchez and colleagues found participants with irritable bowel syndrome (IBS) and comorbid depression and anxiety showed reduced depressive symptoms after a six week course of probiotics, compared to a group who received a placebo. Similarly, a meta-analysis found additional intake of probiotics had a significant effect on the symptoms of people with major depression and a positive effect overall on healthy subjects under the age of 65 (Huang, Wang & Hu, 2016). However, the researchers do highlight the need for further investigation to better understand probiotics’ role in depressive symptoms and draw firmer conclusions.

A few studies have shown some early promising results between probiotics and reduced anxiety symptoms. Tran and colleagues (2019) found participants who took multispecies probiotic supplement had reduced panic and stress symptoms, compared to their peers who received a placebo. However, a meta-analysis of 12 studies found no significant difference in symptoms after taking probiotics. Similarly, Pinto-Sanchez and colleagues (2017) also failed to find a significant impact on anxiety symptoms.

There is no doubt that our brains and our guts are involved in bidirectional communication and that a change in one will affect the other. The prospect of being able to manage difficult emotions using probiotics is indeed an exciting one, but before we start prescribing such a treatment to people experiencing depression and anxiety, further research is needed. In the meantime, there is some evidence that the feeling in our guts may be worth listening to, not only when it’s rumbling for food but also as a sign to address something in our current situation. However, bare in mind it might not always be right!