Did You Know You Have A "Second Brain"? It's In Your Gut.

Have you ever heard the term “gut instinct”, or the phrase “trust your gut”? Some people call it a sixth sense, and others call it a hunch. Whatever your chosen phrase for it, it’s that feeling you get when you just know something. When some type of impulse deep in your gut tells you that you don’t need to think about something more, or mull over your opinion一you can almost feel it tugging there, like some sort of unseen force guiding your intuition.

The scientific explanation behind these gut feelings is that they’re created by our Enteric Nervous System (ENS), an intricate network of neurons and neurotransmitters that are found both in and around the gastrointestinal system or your gut, which is a division of our other nervous systems. When you get “butterflies in your stomach”, you can probably look towards your ENS. And it’s because of this system that some experts refer to our gut as our “second brain”.

At some point in your life, you’ve probably experienced the feeling of looking at a delicious image of food ー or hearing someone describing a dish that sounds especially tasty ー when before you know it, you’re hungry. Your stomach is growling, almost like it’s confirming this idea, even if you didn’t think you were hungry before. Or maybe it’s the opposite scenario: you were in the mood for a bite, but just before you sat down to eat, you saw a deeply unpleasant image that made you lose your appetite. This is the result of your brain sending signals to your gut, whether it’s activating the juices in your stomach to start flowing as it gets ready to digest incoming food, or it’s instigating feelings of nausea or wanting to dispel things from your body (or at least not allow anything else in). It’s no wonder people often say that experiencing some very intense emotions can have a “gut-wrenching” effect. But did you know that it’s not only your brain that can send signals to your stomach? It can also happen the other way around, with your gut sending signals to your brain.

Your ENS contains more than 100 million nerve cells, and it communicates back and forth with your Central Nervous System (CNS). While a key part of its job is to help manage our digestive process, it’s all interconnected with a rather complicated internal system that involves our microbiome. This contains the microbiota, which includes a blend of various microorganisms such as bacteria and fungi that live in our body. Our gut microbes can be affected by various physical factors, but the microbiota also ensure that the body stays in balance, helping it cope with various stresses, keeping the immune system stimulated, and generally making sure that your insides operate in good working order. Their existence and the effect this balance can have on the rest of the body is intimately connected to our nervous system and, in turn, the brain.

It has long been posited that mental health challenges can contribute to digestive problems, but more and more studies are uncovering how experiencing irritation in these gastrointestinal systems can also send signals back to the CNS, instigating or exacerbating mental health issues, as well as possibly having an effect on our cognition. Researchers are finding increasing evidence that digestive or gastrointestinal difficulties such as Irritable Bowel Syndrome (IBS) or functional bowel problems, for instance, can help to trigger changes in our moods and mental state, leading to issues such as anxiety or depression. 

Studies have found that our gut microbiota can have a significant effect on our emotions, moods, and behavior, and that while there are numerous factors affecting the delicate balance of this internal system, a lot of it is down to the bacteria. Even then, decoding what makes for an “ideal” bacterial balance in the gut can be a complex and thorny process. 

The word “bacteria” normally gets a bad rap, but especially in the case of the gut, there are good and bad types, and we do actually need some of them. One of the simplest ways to differentiate between the two is that the “good” bacteria is the kind that can have a positive impact on your health, keeping your internal systems supported. The “bad” kind can have a toxic effect, leading to disease and illness. But it’s not quite as simple as “good bacteria in, bad bacteria out”: In this case, too much of a good thing can also be bad (more on that later), so it’s about making sure there is a healthy balance between the two. 

First, let’s discuss some of the bad guys: Staphylococcus, Clostridium perfringens, and toxic strains of E.coli all count as bad bacteria that can find their way into living in your gut. Some of them can trigger disease and discomfort, while others can lurk inside you relatively harmlessly as long as the rest of your body is strong and healthy, until the body becomes weak (for instance due to you falling ill, or undergoing high levels of stress), when they can turn nasty through adverse actions in your intestines. The way our internal processes function and communicate with each other is so complicated that there is, of course, more to it than this一so much so that researchers are constantly trying to study not just the effects but find the causes. But the simplest way to understand it is that aside from the physical discomfort the bad bacteria could cause, they can also disrupt your internal processes in a way that misfires the way they operate, and that sends incorrect or undesirable signals to the brain. 

The good bacteria, on the other hand, helps us synthesize vitamins, digest food and absorb nutrients, stimulate our immunity, prevent infections, and fight the bad bacteria. They also help to break down and absorb medications, and keep the gut lining healthy, so that bad bacteria and other toxins don’t enter the bloodstream. This is where probiotics ー a combination of this good bacteria and other beneficial yeasts that live inside your body ー come into the picture. They don’t just live in your gut, either一while a lot of them can be found in there, they also exist in the mouth, urinary tract, skin, and lungs, and the vagina (for people who have one). There are various different strains of bacteria that are considered probiotics, including Lactobacillus and Bifidobacterium. Prebiotics, meanwhile, are nondigestible ingredients or types of fiber that help the probiotics. 

The thing that makes this constant battle between the good and bad bacteria more complicated is that it isn’t an all-out war of good versus bad: it’s more like a dance, where your body is trying to find the ideal balance. Too much good bacteria can also have adverse effects, such as belly pain, bloating, indigestion, gassiness, diarrhea, or constipation, to name a few. Why? Because it’s almost like these little soldiers can be too good at their job: too much of them can mean that they won’t just do what they need to do, they’ll go above and beyond一whether you like it or not. If they get to your food before you do, for instance, it can wreak havoc with that delicate, complex system managing your digestion and its related processes. And just like with the bad bacteria, it’s not just the physical discomfort that will have an effect on your mental health一it’s also the fact that the pathways of this incredibly intricate internal network will be disturbed from operating as it ideally or optimally should. 

So how on earth do you find the right balance then一and if it’s all that complicated, then is finding a happy medium even possible, and what are we doing to mess it all up? 

Like most other things in or around the body, finding the right balance for a happy gut isn’t a calculation with a one-time destination: it’s a constantly shifting process. The balance of our gut bacteria can change due to a number of factors, such as our diet or even our age. Even suffering from immense or chronic stress can affect your gut health, creating hormonal shifts and weakening the gut lining or intestinal barrier, that can allow more harmful gut bacteria to enter parts of the body where it shouldn’t be. 

When we experience stress and depression, we have a tendency to reach for foods that don’t just give us an instant fix of pleasure, satisfaction, and energy一our gut microbiota tend to thrive on them too. These mental health challenges can also lead to physiological changes that create inflammation in the gut, further disrupting that delicate balance. It is logical, then, that our diet and mental health can have an effect on our gut health, and it’s important to look after ourselves in a way that allows these pathways to continually find harmony as they communicate with each other back and forth. 

Some of the things credited with creating an unhappy balance of gut bacteria include not having a diverse range of foods in your diet, consuming too much sugar, not eating enough foods that contain prebiotics (such as fiber-rich foods), taking antibiotic medication for a longer term period, or experiencing a lot of stress or chronic stress. Lack of adequate sleep and exercise, undergoing an experience that can put the body under considerable pressure (such as major surgery or trauma), smoking, alcohol consumption, are other factors, while food intolerances, autoimmune issues, and skin troubles can be causal and/or symptomatic of an unhappy gut. 

To combat this, we can try to balance out these issues. Experts have recommended that ensuring a diet full of diverse, nutritious, and fiber-rich foods, staying hydrated, getting regular exercise and enough sleep, keeping our stress levels low, and testing for food intolerances can all help to maintain a happier equilibrium. If an increase in probiotics is needed, they can be ingested through supplements (which can come in various forms, such as pills, powders, or liquids), or through the consumption of probiotic-rich foods. Some popular examples of these include Greek yogurt, sourdough, or fermented foods and drinks such as kimchi, kombucha, and sauerkraut. 

It seems that our mental health can affect our gut health, and that, in turn, healing the gut can have an effect on healing the brain. Scientist Dr. John Cryan, who has conducted extensive research into the relationship between gut microbes and the brain, has explained how the phrase “you are what you eat” can be expanded to “you are what your microbes eat”一and further to this idea, that our brain health can depend on what our microbes are eating. Studies related to these ideas are a cornerstone of nutritional psychiatry and the combination of diet and psychotherapy as treatment, or how one can support brain and mental health issues through diet.

As with any health condition, however ー particularly those that are extremely complex, serious, and deeply interconnected with the rest of our bodily functions ー it is not wise to just self-diagnose and go wild with potential solutions we prescribe to ourselves that could actually do us more harm than good. It’s also worth remembering that our bodies are all unique, particularly when it comes to aspects that can have such a wide range of nuances based on our diet, habits, and lifestyle. Think of it like cooking: while, in theory, anyone given a list of ingredients could prepare a specific dish, the end result could turn out very differently depending on everything from the quantities used to the type of pan, level of heat, and cooking method一and it could taste slightly different to each of us too, depending on our unique taste buds. It is for this reason that if you believe you may be suffering from the effects of imbalanced gut health, we recommend getting in touch with an expert ー such as a qualified nutritionist or dietician, or gastrointestinal specialist ー who may be able to find the right solution for your individual situation. 

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All of the content on our website is thoroughly researched to ensure that the information shared is evidence-based. For more information, please visit the academic journals that influenced this article: Think Twice: How The Gut's "Second Brain" Influences Mood And Well-Being; Gut Feelings–The "Second Brain" In Our Gastrointestinal Systems; 4 Fast Facts About The Gut-Brain Connection; The Gut-Brain Axis: Interactions Between Enteric Microbiota, Central And Enteric Nervous Systems; Impacts Of Gut Bacteria On Human Health And Diseases; Stress, Depression, Diet, And The Gut Microbiota: Human–Bacteria Interactions At The Core Of Psychoneuroimmunology And Nutrition; Exploring The Gut Microbiome’s Connection To Human Behavior