Most people think serotonin is a brain chemical. The "happy hormone" that antidepressants target, something produced up in your head. But here is the part that quietly changes everything: the vast majority of your body's serotonin is made in your gut — not your brain.
This is not a fringe theory. The 90% figure appears widely in scientific reviews, even though how gut serotonin relates to mood is still being researched. And yet the conversation around mood, mental health, and daily energy rarely starts with the stomach. That deserves to change.
Serotonin is a neurotransmitter — a chemical messenger. In the brain, it helps regulate mood, sleep, and appetite. In the gut, it plays a completely different set of roles: coordinating digestion, moving food through your intestines, and signalling back to the brain via the vagus nerve.
That last part is key. The gut and brain are in constant two-way communication through what researchers call the gut-brain axis. Think of it less like a one-way announcement and more like an ongoing conversation.
Specialised cells lining your intestines, called enterochromaffin cells, are the main producers of gut serotonin. They respond to chemical and physical signals in the gut, including what you eat and the products of your gut bacteria. Researchers are still working out how diet, stress, and the gut microbiome shape the way these cells behave.
Here is where it gets genuinely interesting. Your gut is home to trillions of bacteria, fungi, and other microorganisms collectively called the gut microbiome. These microbes do not just help digest food — they appear to influence how much serotonin your enterochromaffin cells produce.
Some research suggests that substances made by gut bacteria, such as short-chain fatty acids from fibre fermentation, can stimulate serotonin production in the gut lining. Much of this evidence comes from laboratory and animal studies, and human research is still developing.
This means your gut microbiome may influence mood in indirect ways. What you feed it is worth thinking about.
A few everyday habits may work against a healthy gut environment. The usual suspects:
There is also a cultural angle worth naming. Many people in Singapore tend to tahan — push through — when they feel off, attributing low mood or persistent fatigue to stress or not sleeping enough. The gut connection rarely comes up in that self-diagnosis.
Diet and lifestyle can influence the gut microbiome, and you do not need a dramatic overhaul — small, consistent shifts are a sensible place to start. Whether this changes mood is still being studied.
Diversity in your diet is linked to diversity in your microbiome. Aim for a wide variety of vegetables, legumes, and whole grains across the week. Adding fermented foods — yoghurt, kimchi, tempeh — has also been linked to a more diverse microbiome in some trials.
Tryptophan is the amino acid your body uses to make serotonin. It is found in eggs, poultry, tofu, nuts, and seeds. Your body needs tryptophan from food to make serotonin, and gut microbes also influence how tryptophan is used.
Serotonin and melatonin are chemically linked, and melatonin helps regulate the sleep-wake cycle. Irregular sleep patterns — common among those working long hours or keeping late nights — may interfere with this. A consistent wind-down routine is a sensible habit.
Some studies link regular physical activity with a more diverse gut microbiome, although results across studies are mixed and research is still developing.
It is important to be clear: gut health is one part of a complex picture. If you are experiencing persistent low mood, anxiety, or mental health challenges, the gut-serotonin connection is not a replacement for professional support. It is a contributing factor worth understanding — not a standalone solution.
Nutrition, movement, sleep, social connection, and professional care all play roles. The gut is one valuable piece of that puzzle.
This article is for general informational purposes only and does not constitute medical advice. If you are experiencing mood disorders, mental health concerns, or persistent digestive issues, please consult a qualified healthcare professional. Do not delay seeking medical attention based on information read here.
Ask Elaine how this applies to your goals and routine — free, no pressure.