It’s home to trillions of microorganisms, including bacteria, viruses, fungi, and other microscopic germs. Welcome to your gut microbiome. It’s housed in your intestines and has been nicknamed the body’s “second brain” ⎯ with research suggesting the gut microbiome is responsible for communicating with the nervous system and immune system, ultimately, yes, affecting overall mood.
That means that what you feed your gut and the health of the microorganisms in it may play a crucial role in how you feel emotionally on a day-to-day basis.
“The gut and brain are connected,” explains Uma Naidoo, MD, a nutritional psychiatrist at Massachusetts General Hospital in Boston and a Harvard Medical School faculty member. Evidence shows that microorganisms in your gut actually produce neurotransmitters in the brain that get used to affect processes like memory, learning, attention, and emotional regulation.
“If there’s an imbalance, that can trip up your mood,” says Dr. Naidoo, who also authored the book This Is Your Brain on Food.
How we fuel our bodies affects how we feel, says Drew Ramsey, MD, an assistant professor of psychiatry at Columbia University and founder of the Brain Food Clinic in New York City. Think about what has happened if you’ve ever tried to sit down and concentrate on a tough project at school or work after eating a large quantity of fast food.
“Increasingly, the microbiome is being implicated in mental health concerns,” says Dr. Ramsey, who is also author of several books, including the most recent Eat to Beat Depression and Anxiety. There are definitely some pretty straightforward dietary changes we can all follow for the sake of improved gut and mental health, he says.
What Are the Ways That the Gut Affects Mood and Mental Health?
Ramsey says research published in the last two decades is starting to explain the gut-brain axis, and why gut affects depression, anxiety, stress-management, and resilience.
Gut Health and Depressive Symptoms
“Just changing someone’s diet can decrease depressive symptoms, which is pretty profound,” says Christopher Lowry, PhD, a behavioral neuroscientist and assistant professor at the University of Colorado in Boulder, where his researches focuses on the role of the gut microbiome in healing post-traumatic stress disorder (PTSD) and anxiety-related disorders.
RELATED: What’s the Connection Between Gut Health and Depression?
A study published in 2017 in the journal BMC Medicine, for example, showed that after a 12-week intervention where patients who had previously been diagnosed with major depression either added a social support group or dietary counseling sessions to their usual treatment — patients in both groups were attending psychotherapy or taking medication — those who started following a healthier, brain-friendly diet improved more. At the end of the trial, 32.3 percent of the participants who focused on transitioning to healthier eating went into full remission from their depression, while only 8 percent of the group assigned to social support did.
Other studies have yielded similar results. A meta-analysis of 41 studies published in Molecular Psychiatry in 2018 showed that a plant-rich, healthy gut diet was tied to a 33 percent reduced risk of depression. On the flipside, a pro-inflammatory diet — that included higher amounts of sugar, processed foods, and saturated fat (foods tied to worse gut health) — was linked to a higher risk of depression.
Gut Health and Stress
More research connects other mood and mental health outcomes with gut health.
In a study published in Brain, Behavior, and Immunity in July 2020, Dr. Lowry found that injecting mice with a bacteria called Mycobacterium vaccae helped protect stressed out rodents against stress-induced anxiety. When the mice were placed with larger, aggressive peers for 19 days, they showed less fear and stress-induced activity, and they were also 50 percent less likely to suffer from stress-induced colitis, and had less inflammation throughout the body.
Lowry is currently working on a clinical trial, funded by the Department of Veteran Affairs, to see if the improving gut health in people has the same effect on stress and anxiety markers.
Gut Health and Resilience
Other work has found that consuming foods ⎯ like yogurt, kefir, kimchi, and sauerkraut ⎯ with probiotics (live organisms, usually specific strains of bacteria thought to increase microbes that may help gut health) may help with resilience to anxiety and other stressors, too.
In a proof-of-concept study, published in 2013 in the journal Gastroenterology, researchers at University of California in Los Angeles, followed 36 healthy women between 18 and 55 for four weeks after splitting them into three groups: one who added two servings a day of probiotic-packed yogurt to their usual diet, another who ate two servings a day of yogurt without probiotics plus their usual diet, and a third control group who continued their usual diet.
At the end of the month, scores on emotion-recognition tasks revealed that the group who ate the probiotic yogurt were calmer, and less alarmed by anger and fear triggers compared with the other groups. MRI scans showed the probiotic group also had lower activity in both the insula (the part of the brain that processes internal body sensations) and the prefrontal cortex (which manages emotion) than the others.
“It suggested to us that probiotics may actually change the way our brains respond to the environment around us, and build our resilience to a stressor,” says lead author, Kirsten Tillisch, MD, chief of integrative medicine at the Greater Los Angeles VA and UCLA professor of medicine, where she researches brain-gut-microbiome interactions and the effects of complementary and alternative interventions on gastrointestinal disorders. (The study authors point out in the paper that the study, however, is small and one of the first trials to show this type of brain-gut communication in people, so the results need to be expanded on.)
Another small study that followed 23 students in Japan preparing for a make-or-break nationwide medical school exam found that adding probiotics to one’s diet may indeed improve self-reported stress, as well as quantitative levels of the stress hormone cortisol.
Why Does Gut Health Affect Mood?
Ultimately the mechanisms behind what may be at play between gut health and mood are still unknown, according to Lowry. But researchers have begun this work and have hypotheses.
For starters, the gut is home to its own nervous system, the enteric nervous system, Lowry says. It doesn’t “think” like the brain does, but it does control digestion and nutrient absorption processes. And it communicates with the brain. Big changes in the gut’s enteric nervous system may send signals to the brain that trigger mood changes, according to Johns Hopkins Medicine. This may explain why disorders like irritable bowel syndrome (IBS), Crohn’s disease, and ulcerative colitis are often tied to symptoms of depression and anxiety. (As Lowry notes, ever notice your tummy and bowels act up when you’re nervous?)
About 90 percent of the body’s serotonin production is produced in the gut, and not the brain, too, says Naidoo. Serotonin, sometimes nicknamed the “happy chemical,” helps regulate mood. Gut bacteria produces a library of neurotransmitters that can affect how we feel, including dopamine, norepinephrine, and gamma-aminobutyric acid, according to a Brain Research paper published in 2019. These chemicals are key players in triggering intense feelings of happiness, reward, or anxiety, Lowry says.
Scientists have also zeroed in on the vagus nerve, which is the crucial component of the parasympathetic nervous system (which controls the body’s ability to relax), as one of the ways the brain and gut are connected. The vagus nerve is able to transfer gut information to the central nervous system, according to a review paper published in 2018 in Frontiers in Neuroscience.
Do These 3 Things to Improve Your Gut Health And Boost Your Mood
Try the following steps that may help boost your gut health, and therefore improve your mood, too:
1. Eat a Rainbow of Vegetables
The microorganisms in our gut break down and feed off of the dietary fiber found in plants, evidence shows. In turn, they produce key metabolites like short-term fatty acids, which are great for gut health, Lowry says.
Different plants produce different metabolites, and the more diverse a mix you consume the better.
“When we eat a plant, we’re eating their healthy microbiome and that contributes to the diversity of ours. This isn’t the case when we eat a hamburger,” Lowry says. Spinach, for example, has 800 different types of bacteria to keep it healthy, he says.
Ramsey says research suggests eating 30 different plants per week may be ideal for bolstering the diversity of your microbiome and optimizing gut health. It’s what Ramsey does. He reaches for kale, blueberries, and cinnamon for a breakfast smoothie, then mixes a salad with yellow peppers, leafy greens, edamame, nuts, and seeds for lunch. That means he’s incorporated eight plants in just two meals. “Getting to 30 plants in a week is not that hard,” he says.
One caveat: If you have IBS, certain vegetables may increase the bacteria that cause and exacerbate symptoms. Know your triggers and which vegetables to avoid, or talk with your doctor if you’re unsure.
2. Experiment With Fermented Foods
Packed with bacteria and yeast, fermented foods are natural probiotics that also increase the diversity of microbes in the gut, Naidoo says. Start adding fermented foods to your diet gradually, Ramsey says. They include:
3. Prioritize Exercise and Sleep
Diet isn’t the only factor that affects gut health. Making sure you’re carving out time for exercise and adequate sleep can help, too, Naidoo says — the Centers for Disease Control and Prevention recommends 150 minutes a week of physical activity while the National Sleep Foundation suggests adults should get seven to nine hours of sleep per night.
Research suggests sleep is connected to gut microbiome diversity. And when you exercise, your body releases feel-good endorphins, oxygen flows better, and research suggests physical activity activates the production of gut-promoting, short-chain fatty acids.
Carve out time to meditate, practice mindfulness, go for hikes outdoors, or whatever may help to alleviate stress, Naidoo says.
“It’s rare that altering your diet is the only thing you need to do for your mental health,” Ramsey says.