Serotonin & The Gut: The Gut-Brain Axis

Your brain and your gut are chatting with each other all the time through hormones and neurotransmitters. This communication channel is known as the gut-brain axis. This system between your brain and your gut is a biochemical and physical network. The gut and brain connection causes that “gut feeling” you get or the “butterflies in your stomach”… that’s real!

Your body communicates in ways you probably don’t even realize. Seriously — your brain and gut are having a nonstop conversation through hormones and neurotransmitters. That said, conventional medicine views the body as a collection of different systems. Its view is that psychological stressors are independent from the rest of the body. However, that couldn’t be further from the truth. The gut and brain connection is real. In reality, our brains are inextricably tied to our gastrointestinal tract. 

In fact, 95% of our serotonin, the key neurotransmitter responsible for regulating mood, is actually made in your gut!

Now, if you’re low on serotonin, you’re more likely to feel the effects of depression and anxiety. As a result, most antidepressants work by keeping more serotonin available in your brain. But what if you could naturally support serotonin production by focusing on your gut health? That’s where the gut-brain axis comes in!

In this article, I’ll talk about the role of serotonin, how it’s tied to your gut health, and four simple ways to pump up your serotonin production. (Hint: it has to do with your gut health!). Let’s explore this relationship between serotonin and the gut. So, what exactly is the gut-brain axis?

The Gut-Brain Axis

As I mentioned, this conversation between your brain and gut is known as the gut-brain axis. It involves your central nervous system (CNS) and your enteric nervous system (ENS).

Your central nervous system consists of your brain and your spinal cord. It controls your thoughts and emotions, breathing, heart rate, body temperature, and the release of some hormones.

Meanwhile, your enteric nervous system, also known as your “second brain,” consists of 200-600 million neurons that move throughout your digestive system. (1) The gut-brain axis is made up of these two systems. 

The ENS works with your CNS. However, your ENS regulates some gastrointestinal functions independently, such as moving food through your gut and bowel movements. Your ENS also controls the release of some neurotransmitters, including gamma-aminobutyric acid (GABA) and serotonin. (2)

Serotonin and other neurotransmitters travel on this gut-brain axis from the gut to the brain via the vagus nerve. This communication superhighway is the body’s longest nerve that emerges directly from the brain. To illustrate, chemical signals travel both from the gut to the brain and vice versa. 

So, if your gut is struggling, you’re more likely to deal with mood swings, anxiety, or even depression. This is where serotonin comes in — it’s the star player in this gut-brain axis drama!

Serotonin: The Super Hormone

Serotonin is one of four “happy hormones” your body produces, along with dopamine, oxytocin, and endorphins. Each of these hormones perform different functions and provide those cozy, happy feelings we all love.

For example: 

• Endorphins are released when exercising. They are our body's natural pain reliever. 

• Oxytocin is released when you show affection to others or animals and gives you those warm and fuzzy feelings of love. 

• Dopamine is what makes you feel proud when you complete a task. 

• Serotonin is the mood regulator. However, it does so much more.

Serotonin acts as both a hormone and neurotransmitter. It is produced in the body. However, your body makes this hormone from the amino acid tryptophan, commonly found in protein-based foods such as turkey.

Not having enough serotonin is linked with depression and in some cases, anxiety. Consequently, many antidepressant medications are designed to block your brain’s serotonin reabsorption. You see, by blocking serotonin reuptake, more of this feel-good hormone is available in your brain. 

Now, let’s get into the relationship between serotonin and the gut. Your gut health has a strong influence on your body’s serotonin levels. As I mentioned earlier, your gut manufactures up to 95% of your body’s serotonin. (3) 

For example, if you’re dealing with chronic digestive issues like IBS, leaky gut, Candida overgrowth, or SIBO, there’s a likely chance your serotonin production is being impaired. 

Having low serotonin creates a vicious cycle. You see, serotonin plays a crucial role in ensuring your body absorbs nutrients properly. 

This interplay between serotonin and the gut is important for your health — both physical and mental. Don’t worry, I’ll tell you how you can boost your serotonin levels in just a minute. First, let me tell you more about serotonin’s role in your body.

What Does Serotonin Do? 

Serotonin is used by your body for many processes. To illustrate, it’s involved in regulating sleep, digestion, and your mood. Here are some of the tasks this super hormone performs in your body:

Serotonin Regulates Your Mood

This “feel-good chemical” is best known for its positive effects on your mood. For example, healthy serotonin levels help you feel calmer, happier, more focused, and less stressed. 

But here’s the thing: Life loves to throw curve balls. When stress hits, your body pumps out cortisol from your adrenal glands to deal with it. 

Let’s face it. Small amounts of stress are just a fact of life. They’re unavoidable. The problem is, when you’re under constant stress, cortisol levels are at their highest. Consequently, this leads to adrenal fatigue.

Serotonin is the hormone that regulates cortisol levels. However, constant stress exhausts your body and impairs the ability of serotonin to function properly. 

The result? You start feeling down, overwhelmed, and even stuck in a funk. As a result, this could lead to full-on depression.

Serotonin Supports Digestion

Now, let’s talk about the gut and brain connection. Remember, serotonin is used to move food through your digestive system and get rid of waste. So, low levels of serotonin may lead to constipation, while high levels may cause loose, watery stools. 

Serotonin also influences mucous secretion in your intestines and appetite. In fact, it helps your body recognize when it’s full. The role of serotonin in digestion is proof of the gut-brain axis. 

Some nerve receptors are responsible for signaling nausea, bloating, and pain. Serotonin is what blocks these signals. However, serotonin levels rise when you eat something toxic or have food poisoning to expel food from your body by vomiting or diarrhea quickly.

The relationship between serotonin and the gut can be seen in those with irritable bowel syndrome (IBS). For example, people with IBS who experience constipation often have lower levels of serotonin. Alternatively, their muscles are less reactive to serotonin causing hard or lumpy stools. Those with IBS that have high levels of serotonin can have diarrhea. (4)

Serotonin Supports Optimal Sleep

Serotonin plays a role in maintaining healthy sleep-wake cycles. To demonstrate, your pineal gland produces the sleep hormone melatonin from serotonin. If you’re low on serotonin, your body will lack the building blocks needed for proper melatonin production. This is why many people suffering from depression experience insomnia as well. (5)

Serotonin Helps With Blood Clotting

Your body releases serotonin to encourage wound healing. Serotonin triggers the narrowing of arteries, which stimulates blood clotting.

Serotonin Supports Bone Health

Research suggests that high levels of serotonin may negatively impact bone health. This is associated with people taking medications designed to elevate serotonin levels. These studies reveal that patients who take antidepressants have lower bone density and are more likely to have osteoporosis. (6)

What Is Serotonin Syndrome?

For optimal health and well-being, you want your serotonin levels just right — not too low or too high. A simple blood test can measure the amount of serotonin in your blood. The normal range for serotonin is 50 to 200 ng/mL.

While low serotonin can lead to many behavioral and mood disorders, high serotonin poses issues as well. For example, when you take medications that increase serotonin action in your body, it can lead to serotonin syndrome. Some of the medications that increase serotonin include: (7)

• Analgesics (tramadol, oxycodone, etc.)

• Anticonvulsants

• Antidepressants (SSRIs, SNRIs, MAOI inhibitors, tricyclic antidepressants)

• Antiparkensonian agents

• Antipsychotics

• Buspirone (used to treat anxiety)

• OTC cold and cough medicines containing dextromethorphan

Serotonin syndrome can cause many side effects. Common symptoms of serotonin syndrome include:

• Shivering

• Heavy sweating

• Brain fog

• Mild headaches

• High blood pressure

• Muscle twitches

• Diarrhea and nausea

Signs of Low Serotonin

If you experience depression or anxiety regularly, you likely have low serotonin levels. Here are common signs you have low serotonin levels:

• Changes in sleep (too little or too much)

• Chronic pain

• Memory loss or dementia

• Little or no appetite

• Cuts that do not heal quickly

• Unable to focus

• Anxiety

• Depression

If you feel you have low serotonin levels, ask your functional medicine doctor to order a serotonin blood test. Now that you understand serotonin’s role in your body and the signs you have too much or too little, let’s talk about how you can boost your serotonin levels naturally.

How To Increase Serotonin Levels

Conventional medicine prescribes antidepressants to boost serotonin. However, as I mentioned, these medications have harmful side effects such as dizziness, insomnia, constipation, and increased feelings of anxiety. (8) They are also very difficult to stop taking and can cause really awful withdrawal symptoms. (9)

The good news is that you can boost your serotonin levels without using medications. Take advantage of the relationship between serotonin and the gut and make some diet changes. Some lifestyle changes can help as well. Here are four ways you can naturally boost serotonin levels:

Eat More Foods Rich in Tryptophan 

You can’t get serotonin directly from food. However, foods rich in tryptophan can boost your serotonin production. It’s a misconception that tryptophan itself makes you sleepy. 

Instead, tryptophan plays a role in producing serotonin, a mood neurotransmitter that relaxes you. It also supports the natural production of melatonin. Because it’s an amino acid, your body can only get it from your diet.

Foods rich in tryptophan include chicken, turkey, fish, and fruits such as bananas, apples, and prunes. Milk is also high in tryptophan. That’s why some people drink warm milk before bed to help them sleep. 

However, dairy is an inflammatory food that causes problems for many people. Dairy foods contain lactose, casein, and whey. Casein is a protein very similar to gluten. Most people who are sensitive to gluten are also sensitive to casein. I recommend everyone eliminate dairy from their diets.

Get More Exercise

As the saying goes, exercise releases endorphins and endorphins make you happy. However, exercise also increases your body’s ability to produce serotonin. While exercise itself does not directly activate serotonin production, it does boost serotonin production indirectly.

It works like this: When you exercise, your gut-brain axis communicates for your body to release tryptophan into your bloodstream and decrease the amount of other amino acids. This gut and brain connection makes it easier for this tryptophan to reach the brain and put you in a better mood.

Aerobic exercise such as swimming, bike riding, brisk walking, jogging, or hiking increases tryptophan levels in your bloodstream. Have you ever noticed that doing these types of activities puts you in a good mood?  That’s tryptophan at work. I love taking walks with my family on a cool fall evening.

Spend More Time in the Sun

One of the main root causes of seasonal depression, or seasonal affective disorder (SAD), is the overproduction of melatonin. Remember, your body produces melatonin from serotonin. Your pineal gland makes melatonin in your brain in response to darkness.

As it gets darker earlier, your body signals it’s time to release melatonin into your bloodstream. (10)

With longer periods of darkness in the winter months, your body uses more serotonin to make melatonin. This is why you may feel more depressed in the winter than in the summer. 

What can you do about it? Spending 10 to 15 minutes outside every day, especially when the sun is shining, has been shown to increase serotonin levels. (11)

Gut Bacteria and Serotonin

The gut and brain connection is critical to our health. Actually, your gut is home to bacteria that help produce serotonin. The fact that people with depression often lack certain species of gut bacteria demonstrates the relationship between serotonin and the gut. As a result, these imbalances in gut flora can lead to mood imbalances. (12)

This is why I recommend everyone take a probiotic to ensure a healthy balance of the good bacteria in their gut. In fact, probiotics are one of the four essential supplements that I recommend everyone take every day to support your gut and brain connection. 

Nevertheless, not all probiotics are created equal. Probiotic strength is measured in colony-forming units (CFUs). The CFU tells you how much bacteria is present in that probiotic. Unfortunately, many probiotics have a short shelf-life and require refrigeration, as CFUs can die off quickly.

That’s why I formulated Probiotic 30 Billion and Probiotic 100 Billion to support this relationship between serotonin and the gut. They each have 14 essential strains to support digestive health and immune function. So, Probiotic 30 Billion is great for daily maintenance, while Probiotic 100 Billion is perfect for rebalancing gut bacteria.

If you have SIBO, though, a soil-based probiotic is your best bet. For example, most probiotics contain lactobacillus or bifidobacterium, which can worsen SIBO by feeding bacteria in the small intestine. In contrast, soil-based probiotics, like Primal Earth Probiotics, are different—they’re designed to survive digestion and make it safely to your gut, helping to restore balance effectively.

The Final Word on Serotonin and the Gut

Your gut and brain are in constant communication through the gut-brain axis. It’s a fascinating system that impacts everything from your digestion to your mood. The connection between serotonin and the gut is a perfect example of how these two systems work together. 

When your gut is healthy and balanced, your serotonin can thrive, helping you feel happier and calmer. On the contrary, when your gut is struggling — whether from poor diet, digestive issues, or stress — it can disrupt this delicate balance between serotonin and the gut.

The good news is you can support this gut and brain connection naturally. For instance, getting regular exercise, eating tryptophan-rich foods, spending time in the sun, and taking a probiotic are all powerful ways to boost your serotonin levels and support your gut health. 

Probiotic 30 Billion is perfect for daily maintenance, while Probiotic 100 Billion offers extra support when your gut needs a reset. And for those dealing with SIBO, a soil-based probiotic like Primal Earth Probiotics is the best bet.

A healthier gut means a healthy you. Start supporting your gut-brain axis today and experience the benefits of a positive gut and brain connection!