Gut and the Brain: How Probiotics Improve Mental Health


Author: Leo Akin
June, 2015


Every year researchers unearth new evidences that confirm that the gut is very important to human health. For example, it is now established that the balance of “good” and “bad” microbes in the gut is essential to the maintenance of the immune system. It is an indication of the importance of the gut microflora that there are 10 times more microbes in the gut than there are cells in the human body. Most of these gut microbes are bacteria. The chief role of the gut florais to prevent pathogens, toxins and other harmful foreign substances from reaching systemic circulation. This is easily achieved as long as “good” bacteria predominate over pathogens in the gut.

The loss of this delicate balance can lead to a number of diseases ranging from inflammatory bowel diseases to skin diseases and even mental health problems. Probiotics can help re-establish the healthy gut flora. Probiotics are live microbes that provide some health benefits for the host.The most important probiotics for human health are bacteria belonging to the Lactobacillus and Bifidobacterium species. Such bacteria can also be found abundantly in certain fermented food products such as yogurt.

Yogurt for the Brain

Yogurt was the source of probiotics in a landmark2013 study (published in the journal, Gastroenterology) that demonstrated the unique relationship between the state of the gut flora and mental health. For this study, 36 women were recruited and then divided into 3 groups. The first group ate probiotic-rich yogurt twice daily for one month while the second group ate a yogurt-like but probiotic-free food product. The third group ate no such product and served as control. Before and after the month-long diet, the differences in the responses of both the affective and cognitive regions of the participants’ brains to visual stimuli were monitored. The results showed that the group who took probiotic-rich yogurt experienced greater emotional stability and improved cognitive functions.

The 2-Way Street Between the Brain and the Gut

Besides the central nervous system composed of the brain and spinal cord, there is an often overlooked nervous system built into the gut. This enteric nervous system develops in the fetus at the same time as the central nervous system and both of them are connected by the vagus nerve running from the brain stem to the gastrointestinal tract. This nerve serves as the conduit between the brain and the gut. On close examination, scientists found that the communication between the gut and the brain is even more extensive than previously believed. For one, the gut sends a lot more information up to the brain then the brain sends down to the gut.

While the 2013 Gastroenterology study was the first to investigate the effects of probiotics on the brain, it was not the first study to identify the communication superhighway between the gut and the brain. In fact, such links were not only established in animals but the benefits of probiotics for mental problems were also well-established in animal models. Take for example this 2011 study published in the Journal of Neurogastroenterology and Motility. It found that Bifidobacterium longum (a probiotic) successful relieved anxiety in a group of mice affected by infectious colitis (due to damage to the gut flora). Another probiotic, Lactobacillus rhamnosus, was also found to influence GABA (gamma aminobutyric acid, the chief inhibitory neurotransmitter in the brain) levels in the brain and lowered corticosterone (a stress-related hormone) levels to reduce anxiety and depression.

Finally, the enteric nervous system also has its own set of neurons similar to those in the brain and even shares some of the same neurotransmitters. For example, a lot more serotonin is produced in the gut than in the brain. Given the fact that serotonin is an important neurotransmitter in the regulation of mood, sleep and cognition, the connection between the gut and brain highlights the importance of functional foods (foods that are both nutritional and medicinal) and probiotics in the treatment of mental health problems.


Taking Probiotics for Mental Health

The results of the Gastroenterology study show that the connection between the brain and the gut is a two-way street. While we know that the brain can send signals to different parts of the body including the gut, the study provides further proof that the gut can also send signals back to the brain. Even the researchers recognized the implications of this study by noting that new drugs for mental health problems should be developed to target the gut flora. However, you should not have to wait for expensive drugs with new side effects to improve your mental health via this gut connection. Probiotics are readily available both as dietary supplements and in fermented food products.

If you decide to take latter, make sure to choose healthy fermented foods. It is advisable that you prepare your own yogurt at home from raw milk. Supermarket yogurts contain unhealthy additives such as sugar, artificial sweeteners, flavors and colorings. Other fermented food products to eat besides yogurt include kefir (also made from fermented milk), natto (fermented soy) and fermented vegetables.

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