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You know that “knot” in your stomach you get when you’re afraid? Or have you noticed that feeling sad or anxious can affect your appetite or the number of bathroom trips you need to make? 😳 It’s not in your head—new research confirms just how much our gut and brain interact, and the connection is stronger than we’d ever imagined.

“Typically when I feel anxious, I’ll get something almost like a stomachache, especially before performances,” says Pearl, a sophomore in San Jose, California. “It feels similar to something being simmered in my stomach—not painful, but quite uncomfortable.”

The gut and microbiome 

Illustration of a happy gut

Research shows that our gut (aka digestive system) plays an essential role in all aspects of health—including brain health and mental health. This is because it digests and absorbs nutrients from our food and gets rid of waste. 💩 When our gut does its job absorbing what we need—and keeping out what we don’t—it helps nourish every single cell in our bodies.

Our gut also houses “friendly” microscopic organisms, aka microbes. This community of microbes—known as the microbiome—includes mostly bacteria, along with yeasts and viruses too—a whole lot of them. In fact, we now know that one person can have more than 1,000 trillion individual microbes in their gut! Holy microbes.

So how do these friendly microbes enhance our health? They:

  • Help break down certain nutrients we can’t use (e.g., fiber) and turn them into nutrients we can use (e.g., short-chain fatty acids, the main source of energy for the cells that line your colon)
  • Crowd out bad microbes we ingest that can cause disease, which reduces the risk of serious gut infections
  • Make certain essential vitamins, like Vitamins B12 and K
  • Have a profound effect on other parts of our bodies—such as our brain and mental health

“The gut microbiome appears to be a rich arena for medical progress,” says Dr. Davis Smith, a physician at the University of Connecticut. We all have colonies of millions of bacteria living inside us. “The relative abundance of different bacteria types seems to have a significant impact on physical and mental health.”

The microbiome-gut-brain axis is a complex one. It involves connections between nerves, biochemicals, and the immune system itself. This is a hotbed of research right now, so we should have more details in the near future, but let’s look at what we know so far.

The enteric nervous system, aka our “second brain”

Your gut has somewhere between 200 and 600 million nerve cells that together form the enteric nervous system. This is often lovingly referred to as our “second brain.” These nerve cells control the intricate functions necessary for your gut to do its job. For example:

  • The release of enzymes to help you digest
  • The movement of food through your digestive system
  • The blood flow around the digestive system that picks up the absorbed nutrients

Basically, the gut uses its own brain to function optimally.

Our happiness neurotransmitter—serotonin—and the gut

One of the most famous mood-affecting neurotransmitters—serotonin—is made in the gut. Serotonin is sometimes called the “happy” neurotransmitter because it seems to be lower in people with depression. Research shows that 90 percent of serotonin is in the gut (not in the brain), and it plays the essential role of promoting the movement of food through the gut.

Stress hormones and the gut

Another important biochemical connection between our microbiome, gut, and brain is through stress hormones. Our HPA-Axis (Hypothalamic-Pituitary-Adrenal Axis) starts in our brains and uses hormones like cortisol to affect other parts of the body, including the gut. A number of studies have shown that stress can alter the gut microbiome. It also appears that the microbiome plays a role in stress-related conditions such as anxiety and depression, though researchers are still working on understanding this connection.

The immune system and the gut

Our gut plays a major role in defending our body against disease, which makes sense since our mouths are portals to the outside world. In fact, over half of our immune cells that produce antibodies—aka the cells that find and attack invaders—are located in the gut.

How food affects your mood

Illustration of gut with foodIt turns out that it may be possible to affect our brain and mood with the foods we eat, according to developing research. A healthy diet is linked with a lower risk of mental health issues. The good news here is we control what we eat. In fact, what we eat is the main thing that influences our gut microbes.

Components of a healthy diet include:

  • Fruits and vegetables
  • Whole grains, nuts, seeds, and legumes (e.g., lentils, peanuts, beans)
  • Fish, poultry, lean red meat, eggs
  • Healthy fats such as olive oil and avocados

Not surprisingly, foods associated with poorer mental health include processed, sugary, salty, fried, and fast foods, as well as sugary drinks. A 2017 study found that when people with depression who ate poor-quality foods (sweets, processed meats, salty snacks) improved their diets over 12 weeks, they reported that their depression symptoms (such as feelings of sadness and tension) improved.

“Usually overly salty foods, such as ramen, are my go-to foods when I’m too lazy to cook for myself. However, these often lead to me feeling unmotivated and very sluggish. Foods like apples, celery, and grapes help counteract that feeling, though, and can help me feel more energized,” says Lusik, a senior in Salem, Oregon.

Probiotics are health-promoting microbes that we can eat, drink, or supplement with. They’re found in fermented foods like yogurt, sauerkraut, kombucha, kefir, miso, and kimchi.

One review of 10 studies found that there may be some mood benefits from taking probiotics. Another review looked at seven studies that compared probiotic supplements to placebos in healthy volunteers. The researchers concluded that there was a significant improvement in psychological symptoms and perceived stress in people who took the probiotics. This research is promising but still preliminary.

Pro tip: Always check with your healthcare provider before taking any supplements, including probiotics. Also, always read labels before purchasing a supplement to ensure that none of the cautions or warnings apply to you, and to ensure you’re taking it as directed.

illustration of stressed gut

Reduce stress for your gut

So we know that gut issues can affect your stress level and moods, but guess what? It works the other way around too. If you have gut issues, then reducing your stress may help.

Stress influences a whole bunch of gastrointestinal functions, such as how well food moves through your gut (motility), the secretion of important biochemicals, and how tightly the gut cells adhere to each other (permeability).

Irritable bowel syndrome (IBS) is considered a “biopsychosocial” disease. This means that it’s not just physical—stress plays a key role in it. In fact, people with IBS tend to have higher-than-normal levels of stress, depression, and anxiety. And people who report high levels of stress can go on to develop gut issues.

In other words, reducing stress can be a big step toward improving a lot of gut symptoms.

Mind-body therapies to improve gut health

Some experts say that the most effective treatments for IBS are mind-body therapies, such as hypnotherapy, mindfulness, and cognitive behavioral therapy. A 2017 review of 12 studies found that mind-body approaches were effective in helping people in China with some of their IBS symptoms.

To improve your gut health, try this

  • Identify what could be contributing to the problem. “Sometimes, associated factors or symptoms can be clues,” says Dr. Smith. “For example, have you experienced a change in diet/meal patterns? Other illness symptoms? Any recent antibiotic use, or increased stress, anxiety, or depression?”
  • Eat more fiber-rich veggies and fruit, and eat fewer processed foods.
  • Try to reduce stress through things like mindfulness, social support, counseling, time in nature—whatever works for you.
  • Eat more fermented foods (e.g., yogurt, kimchi) or talk to your doctor about supplementing with probiotics (remember, this is still an area that needs more research).
  • Get adequate sleep and exercise.
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Article sources

Davis Smith, MD, physician, University of Connecticut.

Avetisyan, M., Schill, E. M., & Heuckeroth, R. O. (2015). Building a second brain in the bowel. Journal of Clinical Investigation, 125(3), 899–907. https://doi.org/10.1172/JCI76307

Bonaz, B. (2013). Inflammatory bowel diseases: A dysfunction of brain-gut interactions? Minerva Gastroenterologica e Dietologica, 59(3), 241–259. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/23867945

Bonaz, B., Bazin, T., & Pellissier, S. (2018). The vagus nerve at the interface of the microbiota-gut-brain axis. Frontiers in Neuroscience, 12, 49. https://doi.org/10.3389/fnins.2018.00049

Brzozowski, B., Mazur-Bialy, A., Pajdo, R., Kwiecien, S., et al. (2016). Mechanisms by which stress affects the experimental and clinical inflammatory bowel disease (IBD): Role of brain-gut axis. Current Neuropharmacology, 14(8), 892–900. https://doi.org/10.2174/1570159X14666160404124127

Burokas, A., Moloney, R. D., Dinan, T. G., & Cryan, J. F. (2015). Microbiota regulation of the mammalian gut-brain axis. Advanced Applied Microbioogy, 91, 1–62. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/25911232

Carabotti, M., Scirocco, A., Maselli, M. A., & Severi, C. (2015). The gut-brain axis: Interactions between enteric microbiota, central and enteric nervous systems. Annals of Gastroenterology: Quarterly Publication of the Hellenic Society of Gastroenterology, 28(2), 203–209. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4367209/

Dash, S. R., O’Neil, A., & Jacka, F. N. (2016). Diet and common mental disorders: The imperative to translate evidence into action. Frontiers in Public Health, 4, 81. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4850164/

Dinan, T. G., & Cryan, J. F. (2016). Mood by microbe: Towards clinical translation. Genome Medicine, 8, 36. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4822287/

Eriksson, E. M., Andrén, K. I., Kurlberg, G. K., & Eriksson, H. T. (2015). Aspects of the non-pharmacological treatment of irritable bowel syndrome. World Journal of Gastroenterology: WJG, 21(40), 11439–11449. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4616219/

Foster, J. A., Rinaman, L., & Cryan, J. F. (2017). Stress & the gut-brain axis: Regulation by the microbiome. Neurobiology of stress, 7, 124–136.
Furness, J. B., Callaghan, B. P., Rivera, L. R., & Cho, H. J. (2014). The enteric nervous system and gastrointestinal innervation: Integrated local and central control. Advances in Experimental Medicine and Biology, 817, 39–71. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/24997029

Gao, J., Xu, K., Liu, H., Liu, G., et al. (2018). Impact of the gut microbiota on intestinal immunity mediated by tryptophan metabolism. Frontiers in Cellular and Infection Microbiology, 8, 13. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5808205/

Jacka, F. N., O’Neil, A., Opie, R., Itsiopoulos, C., et al. (2017). A randomised controlled trial of dietary improvement for adults with major depression (the ‘SMILES’ trial). BMC Medicine15(1), 23.

Jiang, H., Ling, Z., Zhang, Y., Mao, H., et al. (2015). Altered fecal microbiota composition in patients with major depressive disorder. Brain, Behavior, and Immunity, 48, 186–194. Retrieved from https://www.sciencedirect.com/science/article/pii/S0889159115001105?via%3Dihub

Johns Hopkins Medicine. The brain-gut connection. Retrieved from https://www.hopkinsmedicine.org/health/healthy_aging/healthy_body/the-brain-gut-connection

Knight, R., Callewaert, C., Marotz, C., Hyde, E. R., et al. (2017). The microbiome and human biology. Annual Review of Genomics and Human Genetics, 18, 65–86. Retrieved from https://www.annualreviews.org/doi/full/10.1146/annurev-genom-083115-022438?url_ver=Z39.88-2003&rfr_id=ori%3Arid%3Acrossref.org&rfr_dat=cr_pub%3Dpubmed

LeBlanc, J. G., Chain, F., Martín, R., Bermúdez-Humarán, L. G., et al. (2017). Beneficial effects on host energy metabolism of short-chain fatty acids and vitamins produced by commensal and probiotic bacteria. Microbial Cell Factories, 16, 79. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5423028/

Lerner, A., Neidhöfer, S., & Matthias, T. (2017). The gut microbiome feelings of the brain: A perspective for non-microbiologists. Microorganisms, 5(4), 66. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5748575/

Ma, N., Guo, P., Zhang, J., He, T., et al. (2018). Nutrients mediate intestinal bacteria—mucosal immune crosstalk. Frontiers in Immunology, 9, 5. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5787545/

McKean, J., Naug, H., Nikbakht, E., Amiet, B. et al. (2017). Probiotics and subclinical psychological symptoms in healthy participants: A systematic review and meta-analysis. Journal of Alternative and Complementary Medicine, 23(4), 249–258. doi: 10.1089/acm.2016.0023.

Opie, R. S., O’Neil, A., Itsiopoulos, C., & Jacka, F. N. (2015). The impact of whole-of-diet interventions on depression and anxiety: A systematic review of randomised controlled trials. Public Health Nutrition, 18(11), 2074–2093. doi: 10.1017/S1368980014002614. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/25465596/

Pellissier, S., & Bonaz, B. (2017). The place of stress and emotions in the irritable bowel syndrome. Vitamins and Hormones,103, 327–354. doi: 10.1016/bs.vh.2016.09.005. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/28061975

Peppercorn, M., & Kane, S. (2018). Patient education: Crohn disease (Beyond the basics). UpToDate. Retreived from https://www.uptodate.com/contents/crohn-disease-beyond-the-basics

Pirbaglou, M., Katz, J., de Souza, R. J., Stearns, J.C., et al. (2016). Probiotic supplementation can positively affect anxiety and depressive symptoms: A systematic review of randomized controlled trials. Nutrition Research, 36(9), 889–898. doi: 10.1016/j.nutres.2016.06.009. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/27632908

PubMed Health. (2017). What are the organs of the immune system? US National Library of Medicine. Retrieved from https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0072579/

Rogers, G. B., Keating, D. J., Young, R. L., & Wong, M.-L. (2016). From gut dysbiosis to altered brain function and mental illness: Mechanisms and pathways. Molecular Psychiatry, 21(6), 738–748. Retrieved from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4879184/

Science Daily. Sympathetic nervous system. Retrieved from https://www.sciencedaily.com/terms/sympathetic_nervous_system.htm

Sender, R., Fuchs, S., & Milo, R. (2016). Revised estimates for the number of human and bacteria cells in the body. PLoS Biology, 14(8), e1002533. Retrieved from https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.1002533

Tillisch, K., Labus, J., Kilpatrick, L., Jiang, Z., et al. (2013). Consumption of fermented milk product with probiotic modulates brain activity. Gastroenterology, 144(7). https://doi.org/10.1053/j.gastro.2013.02.043

Wald, A. (2015). Patient education: Irritable bowel syndrome (Beyond the basics). UpToDate. Retrieved from https://www.uptodate.com/contents/irritable-bowel-syndrome-beyond-the-basics

Wang, W., Wang, F., Fan, F., Sedas, A. C. et al. (2017). Mind-body interventions for irritable bowel syndrome patients in the Chinese population: A systematic review and meta-analysis. International Journal of Behavioral Medicine, 24(2), 191–204. doi: 10.1007/s12529-016-9589-0

Zheng, P., Zeng, B., Zhou, C., Liu, M. et al. (2016). Gut microbiome remodeling induces depressive-like behaviors through a pathway mediated by the host’s metabolism. Molecular Psychiatry, 21(6), 786–796. doi: 10.1038/mp.2016.44