Have you ever felt butterflies in your stomach? Felt an instant pit when something bad was about to happen? Or felt your stomach twist into knots when you were about to get in trouble? Those feelings are the result of your gut and your nervous system (which includes your brain) working in tandem, and research has shown that gut health and mental health are closely intertwined.
What is the gut-brain axis?
Your intestines—the primary home of your gut microbiome—are lined with nerve cells that communicate constantly with your central nervous system, and vice versa, creating a two-way link between these major body systems known as the gut-brain axis.
“Think of the gut-brain axis like a communication highway that connects the two together,” says Nathan Price, PhD, chief scientific officer at Thorne HealthTech and author of The Age of Scientific Wellness. “The gut and brain are connected in multiple ways. A clear example is serotonin, an important neurotransmitter primarily made in the gut. There have also been recent studies that show microbes in the gut will actually make compounds that travel to the brain and trigger things like hunger cravings for nutrients the gut microbes are looking for.”
Although the scientific and medical communities are still in the early stages of fully understanding the exact why and how behind this link, a large and growing body of research has provided more fascinating insight in recent years. Price says that a healthy gut has a big impact on a healthy brain, and it’s become clear that they’re highly interrelated and communicate with each other often.
“For example, we now know that microbes in the gut make and modulate a variety of key brain neurotransmitters, such as dopamine, glutamate, GABA, and serotonin,” he explains. “The gut microbiome also affects immune signaling and the central nervous system, so the gut can affect both brain function and immune function in the brain.”
In other words, the emotional and cognitive centers of the brain can link with various parts of your gut and send good or bad signals (via chemicals called neurotransmitters), depending on your gut’s health.
The role of inflammation
Inflammation can heavily impact this relationship. Inflammation is often caused by an imbalance in gut bacteria known as dysbiosis, which can cause bad bacteria to enter the bloodstream. A 2020 review, published in the journal Frontiers in Immunology, suggests that dysbiosis also alters the blood-brain barrier, which can lead to inflammation of the brain matter, and these inflammatory pathways have been linked to neuroinflammatory conditions like multiple sclerosis, Alzheimer’s disease, and Parkinson’s diseases.
Megan Hilbert, MS, RDN, a registered dietitian specializing in gut health nutrition at Top Nutrition Coaching says this inflammation can come from ultra-processed foods that tend to contribute to a less diverse microbiome. “There are also food additives that are found in these ultra-processed foods that have been associated with poor gut health outcomes, like artificial sweeteners and emulsifiers like guar gum, soy lecithin and carrageenan,” she says.
The Gut Microbiome and Cognitive Health
Research has found several associations between gut microbiome health and brain health, neurological function, behaviors, and emotions—including connections to Alzheimer’s and Parkinson’s diseases. One small study found that Alzheimer’s disease patients who were given probiotic supplementation for 12 weeks showed significant improvements on mental state examinations (taken before and after supplementation period) compared to a control group.
Certain chemicals metabolized and created by gut bacteria can influence brain function. For instance, research finds that the molecule phosphatidyl choline, which studies suggest is important for helping to stave off dementia, can be turned into the toxic compound trimethylamine N-oxide (TMAO), if the wrong bacteria are present in your gut. Individuals with these bacteria could miss out on its brain benefits, while also creating a molecule in TMAO that can negatively affect the health of your heart. A 2022 study published in Alzheimer’s Research & Therapy found elevated levels of this gut microbial-derived metabolite TMAO in subjects with mild cognitive impairment and Alzheimer’s.
The Gut Microbiome and Mental Health
An increasing number of studies has also begun to show a link between gut health and brain function, behavior, and mood, including various mental health disorders such as bipolar disorder, anxiety, and depression. A 2021 review published in the journal Pharmacological Research found that in patients who had higher levels of Enterobacteriaceae and Alistipes (types of harmful gut bacteria) suffered from depression at higher levels. While those with lower levels of Faecalibacterium (or good bacteria), had lower levels of depression or depressive episodes.
A 2022 study published in the journal Nature Communications looked at the associations between gut bacteria composition and levels of depression symptoms in over 3,000 people across six ethnic groups, one of the largest cohort studies to examine this connection. After adjusting for factors like smoking habits and age, researchers found that “consistent associations between the gut microbiota and depressive symptom levels were confirmed at multiple levels of analysis,” per the study paper, further supporting research on the tie between gut health and mood disorders.
Why is gut health so important?
There are over 40 trillion bacteria in your body, with the majority of them living in your gut. Some studies show that there may be more than 1,000 species of bacteria in the human gut microbiome alone, and because of this, your gut microbiome plays an important role in your overall health by helping control digestion, benefiting your immune system, and preventing chronic disease.
“Having a higher diversity in your microbiome is generally associated with better health,” Price says. “Individuals should want to see an abundance of health-promoting bacteria and a low number of the bacteria known to be disease-inducing.” He adds that looking at what your gut microbiome is achieving metabolically is key because much of the microbiome’s health effects come from compounds that it produces or alters, and that eventually appear in your bloodstream.
Nutrition plays a major role in your overall gut health. Hilbert explains that what we eat also gets fed to these microbes that live inside of us. “The gut is interconnected with so many areas of the body,” she said. “Our brain, skin, immune system, hormones, can all be impacted by the balance of microorganisms that live inside it. These microbes play a role in defending against pathogens, supporting and regulating metabolism, and influencing absorption of nutrients from the foods that pass through our digestive system.”
Easy Ways to Take Care of Your Gut Health
Probiotics and Prebiotics
If you’re looking for an easy way to take charge of your gut health, Dr. Price recommends taking a prebiotic and probiotic supplement, but you can also introduce more prebiotics and probiotics into your gut naturally through certain foods. Probiotics are the live, healthy bacteria in your gut. Certain fermented foods also contain these microorganisms, adding and replenishing the supply of probiotics in your gut. Some fermented foods with probiotics include sauerkraut, yogurt, kefir, cottage cheese, kombucha, and miso. Prebiotics are basically a type of non-digestible fiber that act as food for these microbes, helping them grow and flourish in your gut. Many fruits, vegetables, whole grains, and legumes high in specific types of fiber provide prebiotics to feed your gut flora, including alliums (garlic, onions, and leeks), asparagus, and apples.
There are many pro- and prebiotic supplements available as well, but it’s always best to speak with a healthcare professional when considering adding a new supplement. Adopting a diet rich in probiotic and prebiotic foods is always a great place to start to improve gut health.
Check for Food Intolerances
Food can be medicine, but for some people certain foods may actually trigger an imbalance or inflammation in their gut. If you’re experiencing symptoms like acid reflux, extreme fatigue, gas, nausea, or bloating, it’s possible you may have a food sensitivity or intolerance. You can try eliminating common trigger foods like dairy, gluten, or caffeine to see if your symptoms subside. If you’re unsure how to navigate this, definitely consult with your physician or a registered dietitian with expertise in gut health. And if you’re unsure what foods are best for improving gut health, Hilbert recommends eating a diverse range of plant foods and adding more fermented foods to your diet.
Test Your Gut Health
If you’re curious about the health of your gut, there’s a variety of ways to test it. The most simple is to check your stool after you go to the bathroom. If it looks yellow, red, or black you likely have some infection or your gut has an imbalance.
Another indicator could be how frequently you go number two. Everyone is different, but if you notice yourself running to the bathroom after every meal or only going a few times a week, that might be a sign to look more into your digestion and seek out ways you can improve it with the help of your doctor or another specialist.
And lastly, testing your gut health through at-home or in-office tests is an easy way to get answers directly. They can range in price from $200 to $600, but speaking with your doctor is a smart place to start.