Have you ever had a gut-feeling about something and had to convince yourself that you were making the right decision? Well maybe it’s time to stop second-guessing yourself and start taking extra good care of that gut of yours. DYK that your gastrointestinal (GI) tract and brain are in constant communication with each other? We have known about this relationship for a long time, however, as we continue to learn more about it, an emerging concept is gaining traction – that of psychobiotics – a method of targeting our gut microbiome to positively impact mental health outcomes (1, 2).
The gut-brain axis
The bi-directional link between gut physiology and brain function is known as the gut-brain axis and these two powerhouse organs have a variety of methods that they use to communicate, such as hormone signaling, modulating immune function, gut microbial metabolites, vagal nerve transmission, and the serotonin system.
By now, you probably know how critical the microbiome (collection of microbes, mainly bacteria, that populate your lower intestine) is to immune function, gut health, and other aspects of physiology, but what you may not know is that the microbiome is also a key regulator of the gut-brain axis, and can influence stress-related conditions such as anxiety and depression (1,2).
Microbiome and mental health
Alterations in the gut microbiome can have profound effects on mood, behavior, and our body’s response to stress. Gut microbes produce metabolites, such as short-chain fatty acids (SCFA), that nourish healthy colonic cells and maintain the integrity of the gut barrier to prevent harmful bacteria from crossing through cell walls and triggering an inflammatory signaling cascade. This phenomenon of disrupting the gut barrier is often referred to as “leaky gut” and it has been linked to depression.
Feedback from the microbiome also influences our anxiety-like behaviors and how the body responds to stress, by dampening the activation of the hypothalamic-pituitary-adrenal (HPA) stress axis. Finally, 95% of serotonin (a mood-modulating neurotransmitter) is made in the GI tract from tryptophan metabolism, and certain species of gut microbes stimulate this process. Although the research is still in its infancy, it is undeniable that alterations in microbiota influence brain function and mental health (1,2,3).
What can you do to help?
Diet is one of the factors that modifies the microbiota-gut-brain axis. Healthy gut microbes receive nourishment and produce SCFA by fermenting non-digestible carbohydrates, a.k.a. FIBRE! In other words, the more fibre you eat, the more fuel you are providing to your gut microbiota. Dietary sources of fibre include fruits and vegetables, whole grains, pulses (beans, lentils, chickpeas, and dry peas), soybeans, and nuts/seeds. A good challenge is aiming to eat at least one fibre-rich food at every eating event – give it a whirl.
To take things a wee bit further, there are certain types of fibre that are preferentially fermented by beneficial gut bacteria, and have been shown to confer a health benefit to the host (you!). These specific types of fibre are deemed prebiotics. Some examples of prebiotic foods are garlic, onion, asparagus, bananas, tomatoes, chicory root, rye, barley, and breastmilk. Prebiotics, like inulin, are also frequently added to food products like granola bars and cereals.
And it wouldn’t be an article from me if I didn’t mention fermented foods, which can alter mood and brain activity. The bacteria in fermented foods can help metabolize the prebiotics in your diet, creating more SCFA; and other by-products of fermentation, like lactic acid, can act as anti-oxidants for intestinal cells. So, keep eating your microbes in foods like kimchi, sauerkraut, kefir, and kombucha.
On the flip side, there is evidence that a high-fat, high-sugar diet promotes “leaky-gut”, likely due to a lack of dietary fibre, but also in-relation to inflammation (2,3,4).
Further reading and special thanks for inspiring this article:
1. Foster, J., McVey Neufeld, K. (2013). Gut-brain axis: how the microbiome influences anxiety and depression. Trends in Neurosciences, 36(5), 305-312.
2. Foster, J., Rinaman, L., Cryan, J. (2017). Stress and the gut-brain axis: Regulation by the microbiome. Neurobiology of Stress, 7, 124-136.
3. Morrison, D., Preston, T. (2016). Formation of short chain fatty acids by the gut microbiota and their impact on human metabolism. Gut Microbes, 7(3), 189-200.
4. Marco, M., Heeney, D., Binda, S., Cifelli, C., Cotter, P., Foligne, B., … & Hutkins, R. (2017). Health benefits of fermented foods: microbiota and beyond. Current opinion in biotechnology, 44, 94-102.