We know our diet impacts our physical health. For example, we know that diets high in salt can increase the risk for high blood pressure or that diets high in saturated fat can increase the risk for cardiovascular disease. However, the role of nutrition within mental health is something that, until roughly the last two decades, has been relatively unexplored. With the desire for more treatment options for mental health diseases and the current uptick in research on the role of the gut microbiome in things such as digestion, immune function, and inflammation, the desire to understand more of how (if at all) mental health could be impacted by what we eat has been fueled. If what we eat impacts our physical body, does it not also impact our mental function?
Our Microbiome and Our Mood
Research exploring just this topic has focused predominately on the impact of the microbiome in mental conditions such as Major Depressive Disorder (MDD). Roughly 100 trillion microbes from a thousand diverse species make up the microbiome. It is responsible for promoting digestion, absorption of nutrients, and integrity of the intestines. Changes in microbiome diversity can activate inflammatory responses and the HPA axis which can induce symptoms of depression.1 Research further demonstrates that those with MDD exhibit reduced overall count of microbes as well as reduced microbiome diversity.1 These changes are thought to possibly contribute to symptoms of depression. Therefore, researchers have begun asking can we change our microbiome and if so, can we improve symptoms of depression?
Modifying Our Microbiome
One of the first things that come to many people’s minds when they hear microbiome and gut health is probiotics. However, can these influence our microbiome? Probiotics are microorganisms often found in fermented/cultured foods such as yogurt, kefir, kimchi, or kombucha. They can also be found in supplement form. Probiotics have been shown to aid in maintaining a healthy and diverse microbiome.2 However, these are not the only thing that have been found to change our microbiome. Our microbiome can be impacted by many different things, many of which researchers are still trying to understand. Some things that have been studied for their possible role in influencing our microbiome include fiber consumption, antibiotic use, gastrointestinal illnesses, and high levels of stress.3
When looking at food that can impact our microbiome, research studying the impact of fiber intake have found that intake of the recommended daily amount of fiber increases the diversity of some types of bacteria found in the gut.3 This occurs partly because bacteria within our digestive system ferments dietary fiber as it passes through. This fermentation process encourages formation of a more diverse microbiome.
Researchers have identified that fiber mainly promotes diversity in bacterial types that produce short chain fatty acids (SCFA) during fermentation (strains such as Lachnospira, Akkermannsia, Bifidobacterium, Lactobacillus, Ruminococcus, Roseburia, Clostridium, Faecalibacterium, and Dorea).3 SCFA production has been studied for its role in decreasing inflammation throughout the body as well as its impact on HPA axis activity and systems that regulate neuron growth and maintenance of the blood-brain barrier. All of which impact brain function in regard to mood, learning, memory, stress response, and motivation. SCFA have also been found to influence metabolic responses (such as lowering cholesterol and improving insulin resistance) and promote the health of the intestines.3
Impact of Fiber on Depression
This effect of fiber on SCFA production through promotion of diversity amongst the microbiome has led to hypotheses over the effect of fiber on symptoms of depression. A new study recently published in November of 2020 by Fatahi et al., aimed to explore this connection.
When looking at the relationship between fiber intake and depression, the researchers found that an increased intake of fiber in the diet can lead to a lower risk of developing depressive symptoms.4 It was suggested that perhaps this is due to decreased inflammation, increased production of serotonin, and alterations in the HPA axis brought about by changes in the microbiome – though more research is needed to determine which one of these exactly is occurring.4 Further research has also found evidence that increased fiber intake can even reduce the depressive symptoms experienced by those with MDD.5
Conclusion
Though much of the research is new and we still don’t know a lot about this connection, it is exciting to see possible emerging connections between food and mental health. Especially if this leads to more avenues for research on new management techniques for disease states that have, in the past, only been managed with treatments that have mixed effectiveness. The current treatment for depression (besides talk therapy) involves medications. Though medications can be very beneficial for some, they have been found to only be effective in up to half of those with MDD and can have undesirable side effects. This leaves room to finding other management strategies that can open up the options for treatment. Finding evidence for more potential treatments can help to provide more options for those where the current options may not work. Since research is still new in this area of study, I will definitely be keeping an eye out for any further publications.
-Rachel
p.s. If you are interested in a recipe that incorporates fiber in a fun and tasty way, click here.
This article is for education purposes only and does not aim to make any recommendations. If you are worried or interested about your own health, please seek out recommendations from your own health care provider.
- Limbana, T., Khan, F., & Eskander, N. (2020). Gut microbiome and depression: How microbes affect the way we think. Cureus, 12(8), 9966. Doi: 10.7759/cureus.9966.
- Kim, S., Guevarra, R.B., Kim, Y., Kwon, J., Kim, H., Cho, J.H., Kim, H.B., & Lee, J. (2019). Role of probiotics in human gut microbiome – associated diseases. Journal of Microbiological Biotechnology, 29(9), 1335-1340. Doi: 10.4014/jmb.1906.06064.
- Myhrstad, M.C.W., Tunsjo, H., Charnock, C., & Telle-Hansen, V.H. (2020). Dietary Fiber, Gut Microbiota, and Metabolic Regulation – Current Status in Human Randomized Trials. Nutrients, 12(3), 859. Doi: 10.3390/nu12030859
- Fatahi, S., Matin, S.S., Sohouli, M.H., Gaman, M., Raee, P., Olang, B., Kathirgama, V., Santos, H.O., Guimaraes, N.S., & Shidfar, F. (2020). Association of dietary fiber and depression symptoms: A systematic review and meta-analysis of observational studies. Complementary Therapies in Medicine, 56. Doi: 10.1016/j.ctim.2020.102621
- Swann, O.G., Kilpatrick, M., Breslin, M., Oddy, W.H. (2020). Dietary fiber and its associations with depression and inflammation. Nutrition Reviews, 78(5), 394-411. Doi: 10.1093/nutrit/nuz072
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