Gut Microbiota and Mood: Can you eat your way to happiness?

0:00 Welcome to the Demystifying Medicine Youtube Channel, today we will be discussing the associations found in recent studies between gut microbiota and mood. Major Depressive Disorder or MDD, is a mood disorder associated with persistently low mood, lack of energy, appetite changes, and insomnia, among other things. According to the WHO, Major depressive disorder is one of the leading contributors to the global burden of disease, and so, many studies have looked into the causes of the condition. Researchers believe that depression is caused by a combination of many different factors. They mostly attribute depression to abnormalities in neurotransmitters such as serotonin and dysregulation of neural circuits. They also believe there are environmental components to depression.

0:46 So, high levels of stress in childhood or serious trauma can lead to the development of depression later on. But where does gut health lie in all of this? Researchers have recently tried to understand the associations between gut microbiota and mood disorders. Our gut hosts nearly 10^14 different microorganisms. This complex and dynamic population of microbes, known as the gut microbiota, plays an important role in our health. It controls our digestion, benefits our immune system by protecting us from invading pathogens, breaks down toxins, and synthesizes vitamins. Imbalances between the healthy and unhealthy bacteria in our guts have been associated with different diseases and infections.

1:33 Recent discoveries in the field of microbiology have led us to believe that gut microbes may play a far greater role in our well-being than we once thought. Serotonin is a neurotransmitter or simply put, a chemical messenger, that is considered one of the feel good chemicals along with dopamine. Serotonin helps to regulate mood, happiness and anxiety. It is involved in both sleeping and in waking. Serotonin helps to control your bowel movements and is thought to play a role in regulating appetite. Serotonin also helps to maintain focus and emotional stability. About 90% of serotonin is produced in the gut. Serotonin’s important role in mood and its production in the gut highlights the potential role of the gut in our mood

2:22 You may be wondering what exactly is the connection between gut bacteria and serotonin. Well, certain types of bacteria in the gut are able to produce serotonin. Other bacteria can produce certain metabolites which can stimulate the gut epithelial cells to release serotonin. Serotonin in the gut can stimulate the vagus nerve, which acts as a connection between the brain and gut. Stimulating this nerve leads to the eventual downstream effect of improved mood and increased relaxation. In the first study we explored, researchers looked at the gut microbiota composition for MDD patients. They were able to do this by taking fecal samples and delivering them to a lab,

3:07 where tests are performed to obtain the bacterial counts in the sample. They found that patients with MDD had reduced Bifidobacterium and Lactobacillus bacteria, both of which are involved in making serotonin in the gut. Since serotonin plays a role in mood regulation, it is not surprising to see reduced counts of serotonin-producing bacteria in patients with mood disorders. Particularly in the case of depression, we know that dysregulation of serotonin is one of the primary causes, so understanding the relationship between gut health and serotonin may help us combat that dysregulation. The second study we looked at involved 40 participants diagnosed with MDD and was a randomized placebo controlled trial. 20 individuals received a probiotic supplement and the other 20

3:59 received a placebo. After 8 weeks of taking the probiotic supplement, both groups were compared and the patients who had taken the probiotics had significantly decreased Beck Depression Inventory scores compared to the placebo group. This study found that probiotic administration in patients with MDD for 8 weeks had beneficial effects on mood. As for the third study we explored, it looked at a group of 40 healthy individuals without a current mood disorder. 20 participants received an inert placebo while the other 20 received a probiotic food supplement. Pre and post assessment of mood was done using the Leiden index of depression sensitivity scale. Compared to the participants who received the placebo,

4:45 the probiotic diet group showed a significantly reduced overall cognitive reactivity to sad mood. In other words, this study found that the intake of probiotics may help reduce negative thoughts associated with sad mood. The information we have just presented has several limitations. Firstly, the literature does not provide a clear conclusive answer as to how diet could improve our gut microbiome. The studies which do mention the impact of probiotics on mood, frequently mention that further research is required to reach a conclusive answer. Secondly, we must be cautious with the results from these clinical trials. MDD has a complex mode of inheritance and several factors must be controlled to ensure accurate results.

5:33 Some studies in the space of gut microbiota and mood have flaws such as small sample size or not controlling for gender or age. The third limitation is that there may be a bidirectional relationship between gut microbiota and serotonin. A recent study found that inhibiting the serotonin transporter protein resulted in loss of gut microbial diversity and metabolic capabilities. Serotonin transporter protein expression is also decreased in conditions such as inflammatory bowel disease. These limitations should be taken into consideration when interpreting the information from our video and when doing your own independent research. Understanding the relationship between the gut and mood has many benefits. In one recent study, researchers administered the bacteria Lactobacillus rhamnosus to

6:26 an experimental group of pregnant women. This is a bacteria known to produce serotonin in the gut. Interestingly, these women reported significantly lower levels of depression-like symptoms following childbirth. Probiotics may one day have an important use in regulating mood. And with that said, that concludes our presentation. Our references will be listed in the description below. Please feel free to leave any questions in the comments and thank you for listening.