How often do you see products marketed as able to modify your gut bacteria, promoting “good bacteria” that will improve your overall health? The role of the gut microbiota in health and disease has been used as a marketing tool not only by the food industry through functional foods, but also in pharmaceuticals with the development of probiotic supplements. Indeed, the parallel between gut microbiota and health has become a hot topic in research, with a recent focus on the potential implication of these trillion of gut bacteria in neurodevelopmental disorders, including autism, anxiety and depression (Dietitians of Canada, 2016). However, how much do we really know about the power of these bacteria on our mental health and what foods influence these bacteria?
Let us explore a trending use of functional foods, more specifically fermented foods.
What is a fermented food?
Examples include cheese, butter, yogurt, kefir, sauerkraut, pickles, fermented fruits and vegetables, soy sauce, sourdough bread, and fermented cereals.
Why are these foods considered “functional”?
These food substrates are fermented by our colonic bacteria to yield products that have an effect on our body:
1. Probiotics: bacteria (i.e lactic acid bacteria) that benefits our health. ( “good bacteria”)
2. Prebiotics: products that nourish our “good bacteria”.
3. Biogenics: biologically active metabolites, such as short-chain fatty acids, that directly benefit our health.
What is the basis of the intimate relationship between your microbiome and your nervous system?
The microflora synthesizes functionally active products, and from these products compounds known as neurotransmitters are made, such as, GABA, norepinephrine, serotonin and dopamine. Interestingly, our gut has its own local division of the nervous system: the enteric nervous system, where these neuroactive substances are found to locally act and effect brain activity through mechanisms that may be involved in anxiety and depression (Green, 2018).
Fermented foods are considered beneficial towards maintaining healthy gut microbiota, which may influence overall health. As for its downstream effects on brain function and development and maintenance of mental health, it remains a large mystery at the moment.
Many researchers have also looked into the connection between microbiota dysbiosis and an imbalance in body and mental function, especially relevant during stages of neurodevelopment, as potentially underlying in the development of mental disorders (Tengeler, 2018).
Nevertheless, this field is very current and heavily studied; many are still seeking answers. Indeed, more research is needed as to figure out through what pathways the gut microbiome influences our brain, specifically, whether the neurotransmitters synthesized in the enteric nervous system are absorbed into circulation (Green, 2018).
Lastly, let us take a moment to be in awe of the stature of our microbiome.
Picture this: our gut microbial community hosts 150 times more genes than our human genome does (Ursell, 2014).
Dietitians of Canada. Gastrointestinal system-Microbiota. In: Practice-based Evidence in Nutrition® [PEN]. 2016 July 27.[cited 2019 January 27]. Available from: http://www.pennutrition.com. Access only by subscription. Free trials available. Click Sign Up on PEN login page.
Green, J., Jacka, F. N., Collier, F., Berk, M., Pasco, J., & Dawson, S. L. (2018). Fermented foods, the gut and mental health: a mechanistic overview with implications for depression and anxiety AU - Aslam, Hajara. Nutritional Neuroscience, 1-13. doi:10.1080/1028415X.2018.1544332
Tengeler, A. C., Kiliaan, A. J., & Kozicz, T. (2018). Relationship between diet, the gut microbiota, and brain function. Nutrition Reviews, 76(8), 603-617. doi:10.1093/nutrit/nuy016
Ursell, L. K., Haiser, H. J., Van Treuren, W., Garg, N., Reddivari, L., Vanamala, J., . . . Knight, R. (2014). The Intestinal Metabolome: An Intersection Between Microbiota and Host. Gastroenterology, 146(6), 1470-1476. doi:https://doi.org/10.1053/j.gastro.2014.03.001