The Gut-Brain Connection: The Link Between Gut Health, Anxiety, and Depression

In the health and wellness world today, you might say that gut health is all the rage. Fermented foods, probiotics, prebiotics, and even postbiotics are becoming more and more popular. You might have even heard the popular quote attributed to Hippocrates, the father of modern medicine, that “all disease begins in the gut.” It’s become a favorite saying among many integrative and alternative practitioners. 

At the same time, it’s no secret that we’re also experiencing a “mental health crisis,” in the U.S. and around the world. Forty million adults in the U.S. experience anxiety, about 18 percent of the population. [1About 17 million U.S. adults experience depression, almost 7 percent of the population. [2] The pandemic has heightened these conditions even more, as job loss, isolation, and added stress pile on, particularly among young people, parents, and communities of color. [3]

We used to believe that these two areas, the gut and the mind, were completely separate from each other. But recent research has proved that the body is much more interdependent than we ever thought, and in fact, our gut health may, at least partially, determine our brain health. 

In this blog, we’ll explore the many different avenues connecting the gut to the brain and vice versa, including serotonin and other neurotransmitters in the gut, the brain/gut connection to anxiety and depression, the microbiome and mental health, and more.

The link between gut health and the brain

The more we learn about the body, the more it becomes apparent just how intricately connected all the systems of the body are. 

You probably know that your central nervous system connects your brain to the rest of the body, but did you know that your gut also has a nervous system of its own? This is called the enteric nervous system (ENS), and it’s the reason you feel butterflies in your stomach when you’re nervous or excited. The ENS is so influential that scientists refer to it as our “second brain.” 

It may really be our first brain, considering that our “gut feeling” comes from instinct and intuition, a more innate, ingrained decision-making process rather than a cerebral processing of logical facts. We developed this gut instinct and intuition to avoid danger and survive long before we had the ability to reason. [4]

When you start to see these deep connections between the brain and the gut, it seems like a chicken and egg problem: when we think about treating mental illness, what comes first, the gut or the brain? If the gut is the “older” of the “two brains,” maybe healing it is the key to effectively treating conditions like depression and anxiety. 

Neurotransmitters in the gut

Neurotransmitters are chemical signals that transmit information from a neuron to another cell, whether that is another neuron or any other type of cell. We need neurotransmitters to instruct the cells of our body and keep them operating efficiently. [5]

We associate “neuro” with “brain,” and yet most of the neurotransmitters in our bodies actually live in the gut. Increased or decreased levels of serotonin, dopamine, norepinephrine, epinephrine, acetylcholine and more are associated with a range of gastrointestinal illnesses, from IBS to Crohn’s disease. An astonishing 95% of serotonin alone is found in the large intestine. [6]

It should come as no surprise when intestinal illness initiates a decline in mental health or when anxiety and depression cause gut issues; gut health and brain health are inextricably connected by the presence of neurotransmitters. 

Serotonin production in the gut

Serotonin is one of the neurotransmitters that seems to get a lot of attention, and understandably so. A lack of serotonin has been associated with depression, hence the development of the class of depression drugs called selective serotonin reuptake inhibitors, or SSRIs. 

However, these drugs often end up causing gastrointestinal side effects, showing that a very specific serotonin balance (along with the other neurotransmitters like dopamine) is key to maintaining both gut and brain health. 

Serotonin, also called 5-HT, is inherently produced both in the gut in the enteric nervous system, as well as in the brain and the central nervous system. To make serotonin, the body converts the amino acid tryptophan into 5-hydroxytryptophan (5-HTP) and again into 5-HT—the active form of serotonin. However, tryptophan can also be converted into other metabolites, and these conversion pathways are more dominant. Only 1% of tryptophan goes on to become usable serotonin. [7]

And since, as we mentioned earlier, 95% of serotonin is found in the gut, it’s easy to see how poor gut health can impact serotonin production. 

Conversely, when serotonin is too high, such as when a person is on a high dose of an SSRI for a long time, researchers found that it “enhanced the production of pro-inflammatory cytokines, increased biofilm formation on mouse intestines and worsened intestinal pathological manifestations.” 

Serotonin is a double-edged sword and should be closely monitored in the manifestation of mental health or intestinal illness. While it may be the key to health for some, for others it may be part of the problem. There are so many other factors to consider when we look at the relationship between brain and gut health. 

Stress and the brain/gut connection

Stress—whether psychological, emotional or physical—plays a massive role in both brain and gut health that can’t be ignored. In fact, the Institute for Functional Medicine finds that 75% to 90% of all chronic disease is related to chronic stress and inflammation, as opposed to genetic predisposition. [8]

Stress is the beginning of a downward spiral into disease that can be very hard to reverse. External chronic stressors such as financial insecurity, worrying about loved ones, and lacking purpose or motivation drive up our stress hormones, like cortisol and adrenaline. Constantly producing these hormones takes up an incredible amount of energy from our bodies, leaving us physically and mentally exhausted. 

Perhaps we begin to not sleep well or we aren’t nourishing ourselves properly, compounding the issue. Now the gut is in trouble. High stress, low energy, and inadequate nutrition means that the body has to start prioritizing key systems: digestion slows down, hormones become dysregulated, and the immune response is dampened. Mental symptoms manifest as being easily distracted, frazzled, quick to anger, or low mood. 

Now the body is susceptible to pathogens like parasites and viruses, which disrupt the microbiome. Once the microbiome is imbalanced, the bacteria may not produce enough of key metabolites like butyrate that protect the intestinal barrier. Now we have leaky gut, which can quickly lead to full-body inflammation and disease, including mental illness. 

It all starts with chronic stress. 

How does gut health play a role in anxiety, depression, and other mood disorders?

So the gut and the brain are intricately connected, but what are the actual mechanisms in the gut that cause conditions like anxiety and depression to manifest? It comes down to several, and usually a combination of, different factors. 

The microbiome and mood

Your gut plays host to an entire community of bacteria, fungi, and other organisms that help us digest our food and absorb nutrients–-they even create some of the nutrients we need themselves. This community of microscopic organisms is called the microbiome. 

Over the last several years, we’ve learned more and more about the connection between the health of the microbiome and our health overall, including our mental health. Long story short, it seems that the healthier the microbiome, the better we feel physically and mentally. This usually means: 

  • Pathogens in the gut are few to none.
  • There are more “good guys” than “bad guys,” more supportive organisms that create and process nutrients than ones that steal our nutrients or overproliferate, like candida.
  • Food is easily digested and BM’s are regular, moving toxins and metabolic waste out of the body.

When things are running smoothly with the microbiome and our digestion, we just tend to feel happier, more motivated, more purposeful, and we handle stress easily. [9]


Issues with the gut open the door for inflammation throughout the rest of the body. And full-body inflammation can really put a damper on your mood. 

Leaky gut can also allow toxins to get in the bloodstream that then reach the blood-brain barrier, leading to toxic accumulation in the fatty brain tissue, which is ideal for hanging onto these toxins and storing them. This makes you feel anxious and/or depressed and commonly also causes brain fog and mental fatigue. [10]

Food allergies and sensitivities

Even food allergies and sensitivities can have a huge impact on mental health. Many people, when they cut out gluten or another food that they suspect is affecting them, find that they are happier, calmer, and generally more balanced in the mood department. [11]

Some people find that they do better without these foods permanently. However, once these foods are removed and the gut has had a chance to heal and rebuild, some foods can be slowly added back in and tolerated better. 

Improve your mood and relieve stress by nourishing your gut

Nourishing and rebuilding your microbiome and your gut lining can go a long way towards improving your mental health. There are lots of methods you can use to start moving towards a healthier gut, and it helps to work with a trusted practitioner who can guide you, especially if you’re trying to make big changes in your diet and lifestyle. Here are some of the cornerstone components to start balancing your gut and your brain. 

Food for your mood

Food that supports your mood is food that nourishes your gut, lowers inflammation, and provides abundant nutrients. There are plenty of ways to eat that satisfy these requirements and cater to individual tastes and preferences. But, in general, you should go for the highest quality and the widest variety you can afford, especially when it comes to plant foods. (Avoid pesticides as much as possible!) Here are a few staples you should try to include on the regular. 

  • Grass-fed meat, including liver and organ meats: These meats have the highest amount of bioavailable nutrition over any other food, including vitamin C, B12, A, zinc, copper, and more.
  • Pasture-raised eggs: high in choline, a precursor to acetylcholine, the most abundant neurotransmitter in the body [12]
  • Yogurt/Kefir: Yogurt and its more drinkable counterpart kefir can be great probiotics that support your microbiome. Of course, some people do better with dairy than others. Try goat or sheep’s milk yogurt or kefir if you’re sensitive to cow’s milk. 
  • Beans: Beans get a bad rap for digestion, but when well cooked and added slowly to your diet, they help bind toxins in your bile and carry them out of the body. Try adding a few spoonfuls a day and increasing over time, and always eat your healthy fats separately.
  • Olive oil: Olive oil is an anti-inflammatory fat that has brain boosting properties. Best enjoyed drizzled on at the last minute to finish soups, salads, or really anything you like.
  • Berries: Strawberries, blueberries, blackberries, raspberries are well-known as a healthy part of an anti-inflammatory diet. They are also packed with polyphenols and vitamin C.
  • Chocolate/cacao: We can’t possibly not mention chocolate here, can we? Dark chocolate, particularly cacao, contains tons of magnesium, zinc, and more nutrients that can relax us and relieve anxiety. 

Supplements for stress and gut health

Strategic supplementation can be a great support when rebalancing the gut. To make sure you’re not overwhelming yourself with changes, you’ll want to stick to just a few well-formulated supplements that will get you the most bang for your buck. Here are a few options we like: 

  • Magnesium: Simple magnesium is a cofactor in tens of dozens of chemical reactions in the body, and it’s well known for its calming and balancing effects. Most people are deficient in this key nutrient because of our depleted soils, even if you eat mostly organic. There are many different varieties of magnesium, so you may have to experiment with a couple of different kinds to see what works best for you. 
  • ZincZinc has been getting a lot of buzz lately for its immune-boosting properties, and it's well deserved. But zinc is also critical for digestion and maintaining adequate stomach acid, our first line of defense for pathogens as well as breaking down food. Whether you are already supplementing this key mineral or not, you can easily test your levels by taste using our liquid Zinc.
  • BodyBio Calm: The newest addition to our supplement family launching soon, BodyBio Calm contains just five anti-stress, balance-promoting ingredients: glycine, taurine, Rhodiola Rosea, phosphatidylserine, and manganese. These ingredients were very specifically chosen for their calming effects and are well-tolerated by most people, unlike some other combination supplements. 

Gut-friendly exercise

Most people think that if they commit to an exercise regimen, they have to go hard on the cardio several times a week. But high-intensity exercise can actually increase your stress hormones and create even more inflammation in the gut. 

Lower-intensity forms of exercise like yoga, pilates, strength training, and even simple walking are much easier for the body to tolerate and are more likely to add energy to the body instead of draining it away. If you enjoy cardio, you can still practice 1-2 times per week, but make sure to give your body plenty of rest too. 

Take control of your gut and mental health with BodyBio

With an optimized diet, mindful exercise, and taking steps to reduce your stress, you can positively change your gut and mental health. Supplements are optional in this healing journey, but we have decades of research and testimonials backing our supplements that prove that they can be a valuable addition to your health and wellness.