The Gut - Brain Connection
- Emily EB
- 12 minutes ago
- 5 min read
Recent studies have shown that the gut microbiome (those billions of bacteria, good and bad, that inhabit your intestines) plays a significant role in regulating mood, cognition, and emotional health. In fact, the brain and gut are so well connected, there is growing research that shows that bacteria, together with the cells in the intestines, help make the chemicals that communicate with the brain and nervous system in a two-way information exchange network called the gut-brain axis. Recent studies show that the metabolites produced by the gut microbiome include some neurotransmitters like glutamate, GABA, serotonin, and dopamine. These chemicals are the same chemicals that pharmaceutical medications like Prozac and Lexapro aim to influence. More than 50% of the body's dopamine is made in the gut! (1)
The gut has its own branch of the nervous system, called the enteric nervous system. This system is sometimes called our "second brain" because in it, bacteria make signals or stimulate the intestinal cells to make signals that talk to the central nervous system, including the brain. (2, 3) This is one way that gut bacteria may affect mental health. Differences in gut microbiota have been identified in many brain disorders, including anxiety, depression, anorexia, addiction, schizophrenia, ADHD, autism and dementia. While you are NOT "what you eat," digestive health seems linked to mental health.
Beyond mental health, the gut microbiome can impact the immune system, the skin, the endocrine system, reproductive system and cardiovascular system. By supporting a diverse gut bug environment, you can impact not only your digestive health, but all these other systems and mental well-being.
Of course, diversity of gut bugs makes for a stronger community, which in turn strengthens the organism and all its systems. The goal is not to have ONLY friendly bugs, it's to have balance and diversity of bugs. We don't really know what the right balance is, so for now, all we can do is feed our guts the things that we know help produce a general sense of balance and diversity.
What influences our gut microbiome?
Diet- a diet that includes probiotics and prebiotics is most helpful to our gut microbiome
Lifestyle- exercise, good sleep, and low stress seem to correlate to a healthier microbiomes
Antibiotics- these can be lifesaving, but they also destroy the good bacteria that our microbiomes rely on to keep us healthy. If you don't really need an antibiotic, it can do more harm than good to take one
Alcohol- this can interfere with the delicate balance of the microbiome
What are probiotics?
Probiotics are actual living microbes--usually bacteria, but sometimes yeast. If you consume them, they can help create a better balance between helpful and harmful microbes in your microbiome. Probiotic microbes use fermentation to do their jobs, including helping us to digest fiber and other nutrients. Foods that have undergone fermentation during the food preparation process naturally contain probiotics, like yogurt (though not all yogurt), kefir, sauerkraut, miso, kombucha, and kimchi. Not all fermented foods have living microbes that can help the gut. For example, beer and wine, sourdough bread, chocolate and tempeh are all fermented foods but they don't contain live probiotic microbes.
What are prebiotics?
Prebiotics encourage good bacteria in your gut to grow. As a general rule, plant-based foods have prebiotics. Some are especially helpful to good bacteria, like asparagus, artichokes, onions, garlic, leeks, oatmeal, bananas, chicory root, honey, and beans.
What about alcohol?
Alcohol can significantly impact the gut microbiome by increasing the presence of harmful microbes and decreasing beneficial ones-- a condition called dysbiosis. Some studies show that drinking occasional small amounts of red wine can have positive effects on the microbiome, but the preponderance of evidence suggests alcohol has a detrimental effect on a well-balanced microbiome. Basically, at this point, we just know that it's complicated, and moderation is important.
So should I ditch my Prozac for sauerkraut?
No. An extremely profitable supplement market in the US would like you to believe that THEIR probiotic/prebiotic is the cure for all your ails, but we still don't know enough about which strains of probiotics are useful in which conditions, and what the exact balance should be, in order to safely use them as real treatments. Many types, or strains, of probiotics are promoted and sold for a cornucopia of conditions, but not all of them have been researched or shown to be helpful. Not all brands are of the same quality, and many have fillers added that can impact the body as well. The bottom line is we just don't know the right doses yet, so it's not recommended to take probiotic supplements just to take them.
There are some well-researched strains of probiotics that can temporarily help certain conditions like preventing the gastrointestinal side effects of antibiotic use like bloating and diarrhea. And newer research has shown that taking probiotics at the same time as antibiotics appeared to prevent or reduce some of the detrimental changes to the gut microbiome associated with antibiotic use. (4) The University of Wisconsin's Family Medicine Department of Integrative Health has a free helpful handout detailing which probiotic to take for certain gastrointestinal conditions: https://www.fammed.wisc.edu/files/webfm-uploads/documents/outreach/im/handout-probiotics-for-specific-conditions.pdf.
Studies have shown that patients with a mental health condition like depression have gut dysbiosis, or a disturbance in their ratio between "good" and "bad" gut bacteria, we still aren't sure whether that's the cause of depression, or just associated. Which came first?
Science is narrowing down potentially helpful bugs for certain mental health conditions. The microbes Lactobacillus spp. and Bifidobacterium spp. are the most widely studied probiotics in depression. A small number of studies have demonstrated that Lactobacillus and Bifidobacterium counts were significantly lower in patients with Major Depressive Disorder compared to healthy counterparts. Exactly how much should be added back, or whether there needs to be other bugs involved in the balance, is still unclear. In fact, the role of probiotics in treating depression and other mental health disorders is unclear, but some studies have shown that using certain probiotics to restore the balance in the gut microbiota positively impacts depressive symptoms. In short, we humans, and our gut bug buddies, crave balance. Go figure.
The takeaway
We could drive ourselves crazy obsessing over getting enough probiotics and prebiotics in our diet to support our gut bugs, but that wouldn't evoke the idea of "balance" that seems to make it all work best. Instead, it's more helpful to know that certain foods as super helpful to your brain-gut connection. We have a sense of what those foods are, and our bodies know what to do with them. Try your best to work in natural probiotics and prebiotics where you can in meals. But as a busy human, extend yourself some grace to cut corners, too. (I add Benefiber to my water because it's an easy, relatively tasteless way to get more fiber in the day. I try to eat at least 3 colors with each meal but if I don't have time for that at one meal, I make up for it later in the week.) Most importantly, our guts want us to live balanced lives. On this one at least, we should listen to our gut.
Take good care,
Dr. Holt
References:
Kelly JR, Kennedy PJ, Cryan JF, Dinan TG, Clarke G, Hyland NP. Breaking down the barriers: the gut microbiome, intestinal permeability and stress-related psychiatric disorders. Front Cell Neurosci. 2015;9:392. doi:10.3389/fncel.2015.00392
Bested AC, Logan AC, Selhub EM. Intestinal microbiota, probiotics and mental health: from Metchnikoff to modern advances: Part II - contemporary contextual research. Gut Pathog. 2013;5(1):3. doi:10.1186/1757-4749-5-3)
Paper published in the Journal of Medical Microbiology: https://www.microbiologyresearch.org/content/journal/jmm/10.1099/jmm.0.001625
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