Serotonin is widely known as a “feel-good” neurotransmitter in the brain, but surprisingly, about 90-95% of the body’s serotonin is actually made in the gut [1]. So what does this mean for your digestion and mood? Specialized cells lining the intestines synthesize serotonin in response to food and other stimuli, effectively making the gut our largest serotonin factory [1]. Far from just influencing mood, this gut-derived serotonin plays crucial roles in regulating digestive functions: it stimulates intestinal muscle contractions, modulates fluid secretion, and even helps sense pain or fullness in the gut [1,2].
As you may expect, if you’re a recurring reader of this blog, the serotonin produced in our digestive tract also communicates with the nervous and immune systems, forming a key link in the “gut-brain axis” that connects our gastrointestinal health with our mental state [1,3]. Although the details of the gut-brain conversation are still unfolding, one message is already loud and clear: serotonin made in the gut plays a starring role in both digestion and mood. In the sections ahead, we’ll explore how it guides bowel movements, how it connects with the brain, and what everyday choices can help keep this system in balance.
The Role of Serotonin in Bowel Movements
In the gastrointestinal tract, serotonin works much like a conductor, orchestrating how the intestines move and function. When the tempo is too fast, the rhythm becomes disordered; when it slows too much, movement stalls. This same chemical messenger not only keeps digestion in tune, but also affects our emotional state.
Scientifically, the process begins when food enters the gut: enterochromaffin cells release serotonin, which then stimulates nearby nerves and intestinal muscles to propel contents forward (peristalsis) and to secrete fluids. In this way, serotonin helps determine the pace of intestinal transit. High levels accelerate motility, sometimes producing cramping, while low levels slow transit, contributing to constipation [4]. Clinical observations reinforce this: people with irritable bowel syndrome (IBS) often show serotonin imbalances. Those with diarrhea-predominant IBS (IBS-D) may have excessive serotonin release after meals, while those with constipation-predominant IBS (IBS-C) tend to show reduced serotonin signaling [4]. These differences help explain their symptoms: whether the intestines move too quickly or too sluggishly.
Beyond motility, serotonin in the gut shapes how we feel things like bloating or abdominal pain. It even helps maintain the health of the gut lining and supports the immune system in the intestines. That’s why drugs for gut problems, and even common antidepressants, often affect digestion. Too much or too little serotonin can throw off bowel rhythms [3,4].
The Gut-Brain Axis: Serotonin and Mood
The influence of gut-derived serotonin extends well beyond digestion. Although serotonin produced in the intestines does not cross the blood-brain barrier, it communicates with the brain through the gut-brain axis: a complex network of neural pathways, signaling molecules, and immune mechanisms connecting the two. When serotonin is released in the gut, it can activate vagus nerve endings and enteric neurons that send signals up to the brain, effectively letting our central nervous system know what’s happening in the GI tract [2]. This is one reason we experience “butterflies” or urgency when we’re nervous: our gut “feels” stress and sends signals to the brain, and vice versa. Notably, a large proportion of people with chronic digestive disorders also experience anxiety or depression, underscoring the bidirectional link between gut health and mental health [5,6]. For instance, IBS (which affects around 10% of the population worldwide) frequently coexists with mood disorders, and psychological stress can trigger or worsen symptoms. Therefore, digestive conditions are now classified as disorders of gut-brain interaction rather than purely “bowel” conditions [3].
When serotonin signals in the gut are out of balance, they can disrupt communication with the brain, affecting mood and even cognition [2,3]. Conversely, disturbances in the brain (such as chronic stress or anxiety) can alter serotonin release in the gut, potentially provoking bowel symptoms. The gut microbiome is another piece of this puzzle. Trillions of bacteria in our intestines can affect serotonin levels by producing certain metabolites and even some neurotransmitters themselves. In fact, some gut microbes help increase the host’s serotonin production by boosting intestinal tryptophan metabolism (tryptophan is the amino acid precursor to serotonin) and by stimulating enterochromaffin cells to release serotonin [2]. Scientific studies have shown that altering the gut’s microbial composition can change serotonin activity: for example, certain probiotic bacteria have been found to improve mood and reduce anxiety, potentially by increasing gut-derived serotonin availability [2,9]. Some probiotics have been linked to benefits beyond digestion. Early studies suggest that certain strains, sometimes called “psychobiotics,” may help ease stress and low mood by supporting the gut’s ability to produce calming brain chemicals like serotonin. For example, Bifidobacterium longum has been shown in people to modestly improve symptoms of depression and stress, presumably by positively influencing gut neurotransmitter systems such as serotonin production [2].
Together, these findings show that the gut’s serotonin network is a two-way street: it influences how we feel, and our mental state in turn shapes digestion. This makes caring for both gut and mind essential: a theme we’ll translate into everyday strategies in the next section.
What Can I Do Today?
Understanding the dual impact of gut-derived serotonin on our digestion and mood naturally brings up the question: how can we support a healthy serotonin balance through everyday choices? Fortunately, several lifestyle and dietary strategies can help nurture both gut and mental health:
- Eat a gut-friendly, tryptophan-rich diet: Plenty of fibre from vegetables, fruits, whole grains, and legumes supports a diverse microbiome and healthy serotonin production [2,7]. Soluble fibre, such as oats, barley, or psyllium, can ease constipation and overall symptoms, while too much insoluble fibre may worsen bloating for sensitive people [7]. Include fermented foods like yogurt, kefir, sauerkraut, and kimchi, and add tryptophan-rich foods such as poultry, eggs, dairy, nuts, seeds, and mango [4]. Limit ultra-processed, high-fat, high-sugar foods [4]. If you have ongoing gut issues, a short-term low-FODMAP plan with a dietitian might reduce symptoms and improve quality of life [7,8].
- Consider probiotics: Certain strains, sometimes called psychobiotics, may support both digestion and mood. For example, Bifidobacterium longum has shown benefits for stress and mild depression in early studies [2,9]. Even adding probiotic-rich foods like kefir or yogurt can help maintain microbial diversity.
- Move your body: Exercise keeps the gut moving and can reduce stress. Regular activity boosts serotonin and endorphins, improving both digestion and mood. Studies link exercise to fewer IBS symptoms and better quality of life [10]. Aim for at least 20-30 minutes most days.
- Manage stress and sleep well: Stress disrupts serotonin and gut sensitivity, while poor sleep harms both microbiome and mood. Mindfulness, deep breathing, or therapy can calm gut-brain feedback loops. Consistent, restful sleep supports a daily reset for both body and mind [2].
- Seek professional guidance: If gut or mood issues persist, consult a healthcare professional. Because IBS, anxiety, and depression often overlap, treatment may need to address both the body and the mind: a holistic approach that combines medical care with lifestyle and psychological support.
Your Gut, Your Mood, Your Move
Your gut makes most of your serotonin, and the way you eat, move, and manage stress shapes how well that system works. Taking small, daily steps can help you support both digestion and mood.
Learn more about serotonin in the blogs below:
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