You feel down, drained or easily irritated. Your head feels restless, your concentration is gone and your memory keeps letting you down. You know something isn't right, but medical tests find nothing and your symptoms are blamed on stress or your age. Almost no one makes the link to the place where many of these symptoms can come from: your gut.
Maybe you recognise this: you've had gut problems for a while, or the diagnosis IBS, Crohn's or colitis. You notice that your mood moves with your gut. When things are going badly in your gut, you also feel more down, more tired and more tense. That this happens is no coincidence, and no, it isn't all in your head. Because your gut and your brain are in contact with each other all day long.
That connection is called the gut-brain axis. In this article you'll read how it works, why a disrupted gut can contribute to low mood, anxiety and a foggy head. And above all: that the cause behind your symptoms can sit in your gut, and that you have influence over it.
Your gut: your second brain
We're taught that the gut is a kind of tube running through the body where the food you eat gets processed. That's true, but it's only a fraction of the story. In your gut wall lies a nervous system of its own, the enteric nervous system, with hundreds of millions of nerve cells. That's more than in your spinal cord. It's no coincidence your gut is also called your second brain.
That second brain is in constant contact with the brain in your head, and that contact goes both ways. So your gut feeling is real: it's your gut sending a signal upward. And the other way around, you feel tension in your head almost immediately in your belly.
The most important direct line between the two is the vagus nerve, a large nerve that runs from your brainstem all the way down to your belly. You can think of it as the motorway between your gut and your head, with traffic going both ways all day long. On top of that, your gut and your brain talk to each other through substances in your blood: hormones, inflammatory messengers and compounds your gut bacteria make. And it's precisely in that last conversation, the one from your gut bacteria, that things often go wrong.
Is serotonin really made in your gut?
You may have heard that about 95 percent of your serotonin, often called the happiness hormone, is made in your gut. That's true. But there's an important nuance behind it that is almost never told.
The serotonin made in your gut mostly does local work. It drives the squeezing motion that pushes your food through your digestion, the peristalsis, and regulates how sensitive your gut is. This gut serotonin does not cross the blood-brain barrier. So it doesn't simply flow up into your head to make you happier. Your brain makes its own serotonin.
So how does your gut influence your mood? Mainly through the supply of a building block. Serotonin is made from tryptophan, an amino acid from your food, and that tryptophan does cross the blood-brain barrier. As long as there's enough tryptophan available and production runs smoothly, you're fine. But there's one thing that can hijack that whole process: inflammation.
How inflammation lowers your serotonin
This is the part my own research dwelled on, and it's perhaps the most important link in the whole story.
The paragraph below can feel quite technical. It's here to explain the mechanism for those who find it interesting. When there's a low-grade or actual inflammation somewhere in your gut or your body, your immune cells release inflammatory messengers called cytokines. These switch on an enzyme called IDO. That enzyme reroutes tryptophan. Instead of tryptophan being turned into serotonin, it now goes another way, the kynurenine pathway, which belongs to your body's immune response. This has two downsides: there's less left to build your serotonin from, and more compounds are formed that can actually lower your mood.
This is not a fault in your body, but an ancient defence mechanism: when your immune system becomes active it claims the tryptophan, partly to deny pathogens that building block and partly to steer the immune response. Your mood and how you feel during the day pay the price for it.
This isn't guesswork. In people with chronic gut inflammation, researchers see exactly this pattern: lower tryptophan levels and a higher kynurenine-to-tryptophan ratio, and that correlates with how severe the symptoms are. In other words: as long as an inflammation keeps smouldering in your gut, your mood is, as it were, left empty-handed when it comes to the building block it needs. And that explains why low mood or depression and gut problems so often go hand in hand.
Gut bacteria and your mood
Serotonin isn't the only one. Your gut bacteria are also involved in making other messenger substances your brain works with. Some species influence GABA, the substance that calms your brain, and others play a part in the system around dopamine, which has to do with motivation and energy.
Researchers at the University of Leuven mapped the microbiome of more than a thousand people and saw that two bacterial groups, Dialister and Coprococcus, were clearly less present in people with depression. It's precisely those bacteria that are involved in producing butyrate and in the dopamine system. It's no proof that the bacteria cause the depression, but it does show how closely the make-up of your gut flora is linked to how you feel.
That makes something clear: a balanced gut flora doesn't just give you good digestion, it also supports the substances your brain works with.
Butyrate: fuel for your gut and brain
One of the most important substances your gut bacteria make is butyrate. It's formed when they ferment the fibres from fruit and vegetables. Butyrate is the fuel for the cells of your gut wall and it helps maintain the protective mucus layer made on your gut wall. But it goes further than your gut alone.
Butyrate has an anti-inflammatory effect, and that effect reaches into your brain. Your brain has its own immune cells, the microglia. If they become overactive, a smouldering inflammation arises in your brain, and that's linked to low mood, fatigue and that foggy feeling in your head. A gut flora that makes enough butyrate helps keep that fire under control. A flora that's out of balance and makes little butyrate does the opposite.
Leaky gut and your brain
This is where the different factors come together. A disrupted gut flora makes less butyrate, so your gut wall gets less fuel and the protective mucus layer becomes thinner. Because of the reduced protection, the gut wall can become damaged, leaving less control over what passes through your gut wall and is absorbed into your body. This is also called a leaky gut.
Through that weakened gut wall, substances leak in that normally shouldn't get through, such as small fragments of bacteria we call LPS, gut flora bacteria and insufficiently digested food particles. When your immune system encounters these intruders, it reacts. At first quietly, without you noticing. But if this situation continues for a long time and your immune system has too few nutrients to stay strong, it switches to a back-up system. This first creates low-grade inflammation, and it's a matter of time before it becomes chronic inflammation. This inflammation doesn't stay put in your belly. The inflammatory messengers travel along in your bloodstream through your body, where they can irritate the blood-brain barrier and so activate the microglia in your brain. And that closes the circle: a problem that started in your gut you can ultimately feel in your head, as low mood, irritability or a head that just won't think clearly.
Stress and your gut: it works both ways
The gut-brain axis is a two-way street, and that's certainly true for stress. When you experience stress it slows your digestion, and it's a matter of time before this disrupts your gut flora. You may know it from the knot in your stomach before a nerve-racking moment, or from other stressors like money worries, or racing through life because you're always fighting the clock. It works the other way around too: when there's an inflammation in your gut, caused by a disrupted gut flora, the presence of a parasite or food intolerances, then your gut sends stress signals to your brain and keeps your stress system switched on.
With long-term stress, something else comes on top. Your body then becomes less sensitive to cortisol, your most important stress hormone. Cortisol is normally one of your strongest anti-inflammatories.
If you become insensitive to it, your body loses one of its most important brakes on inflammation, exactly when you need it most. That's how chronic stress and chronic inflammation keep each other going.
It's also the reason that for inflammatory complaints and chronic inflammatory diseases such as Crohn's and colitis, corticosteroids like prednisone are often prescribed, because this is high-dose, factory-made cortisol that switches off the immune system so the inflammation stops.
In all this, the vagus nerve is an important brake: it stands for rest and recovery. Anything that activates that nerve, such as calm breathing, good sleep and exercise, soothes not only your head but also your gut. It's no coincidence that people with chronic gut problems often also feel tense, tired or down. It's the same system that's out of balance on both sides. Read more about stress and your gut.
Try this breathing exercise to lower your stress: breathe in calmly for four seconds, then breathe out over six seconds. Rest two fingers or your hand just below your navel. Breathe consciously into the lower part of your belly, so your hand rises forward. Do this for at least 1 minute, and if you have the time, set a timer for 5 minutes. Take your time, sit quietly and focus only on your breathing. You'll probably feel your muscles relax during these minutes and feel more calm in your body.
The link between your gut and your liver
That low-grade inflammation and those LPS that have entered your body through your gut wall don't just trouble your brain. Through your blood they also reach your liver, because everything absorbed from your gut passes through your liver first. A liver that constantly has to put out small fires because all kinds of unwanted things come in through your gut wall becomes overloaded over time. In this way, the same disrupted gut that lowers your mood can also contribute to a liver under strain. On top of that, LPS act as so-called danger signals: they tell your body that something isn't right, which in itself is again a factor that activates the stress system.
If you want to know exactly how that works, read this article on fatty liver. It shows how your gut, your head and your organs work together and cannot be separated.
Gut problems and your mood with IBS, Crohn's and colitis
If you have IBS, Crohn's or colitis, this story is probably extra recognisable. Functional gut problems strikingly often go together with low mood, anxiety, chronic fatigue and something we call sickness behaviour. You don't feel like going out, no new adventure, not the busyness of a birthday party. Maybe you, or those around you, notice that you're withdrawing. You keep to yourself, you live a little more on your own and have little urge to do anything. This is, as you read earlier, because the same gut-brain system is out of balance. That doesn't mean you're imagining it. It means the two share the same root, with your body in survival mode. That's exactly why, with gut problems, we never look only at the belly, but at the whole system around it.
What you can do for your gut-brain axis
The hopeful thing about the gut-brain axis is that on the gut side you have a lot of influence, and that influence carries through into your head.
- Feed the butyrate-forming bacteria of your gut flora: fibres from vegetables and fruit are their fuel. Here it's important to choose the organic variety as much as possible. The pesticides on non-organic vegetables and fruit can have a negative effect on your gut flora. If you currently take in only a little fibre, build it up gently in small portions so your gut flora can get used to it, and steam vegetables first so they're easier to digest.
- Tackle the inflammation: investigate the cause of your gut problems with a food intolerance or stool test, so you can work in a targeted way to address the cause of the inflammation.
- Choose the right food for your body: eat fewer products with refined sugar and fast carbohydrates so your blood sugar stays stable. Eat more vegetables, fruit and good protein sources such as beef, chicken, herring and salmon.
- Work on your vagus nerve: do the breathing exercise, get enough regular sleep, and move every day, such as a walk right before or after eating. This way you activate the rest-and-digest side of your nervous system, and calm your gut and your head at the same time.
Finally, it's important to mention: if there really is a disruption in your gut, such as a bacterial overgrowth, a parasite or a fungus, this rarely recovers on food alone. In that case a targeted approach is needed. With a stool test we map the make-up of your microbiome: how your gut flora is composed, whether pathogens are present, how active your immune system is in your gut, and how well your digestion is running. If you want to go deeper into your microbiome as a whole, you can read this article about your microbiome.
In 2015, Jeroen was diagnosed with Crohn's disease. At the time he was told he could only take medication and, with bad luck, surgery. Food would have no effect on his symptoms. He refused to accept that, went looking for the cause himself, and was symptom-free within six months, without ever having used medication.
That search, his own experience, and his training as an orthomolecular therapist working with hundreds of people, form the basis of our guidance. Want to know what we can do for you? Schedule a free 30-minute intro call. Together we look at where you stand, what you've already tried and whether our approach fits you. No obligations, no sales pitch, just an open conversation that gives you new insight into the steps you can take to restore your health.