For years, we've associated serotonin solely with the brain. We call it "the happiness hormone." We link it to mood, motivation, and well-being.

But there's a fact that changes the perspective:
Approximately 90% of the body's serotonin is produced in the gut. Not in the brain.

Understanding this isn't about simplifying emotional well-being. It's about broadening it. Because mood isn't just mental: it's also biological. And the gut microbiota is a key part of that system.

What exactly is serotonin?

Serotonin is a neurotransmitter: a molecule involved in cell communication and the regulation of essential functions.

Among others, it's related to:

• Mood regulation
• The sleep-wake cycle
• Appetite and the feeling of satiety
• Intestinal motility
• The stress response

Why is so much serotonin produced in the gut?

The gut is not just a digestive organ. It's a neuroendocrine center and an integration point for the immune, hormonal, and nervous systems. And it's where your microbiota lives: an ecosystem made up of billions of microorganisms.

In the gut, there are specialized cells (enterochromaffin cells) that produce a large part of the body's serotonin. And this production doesn't happen in a vacuum: it's influenced by the state of the gut ecosystem.

Factors influencing this production

• Availability of tryptophan (amino acid precursor to serotonin)
• Intestinal inflammation and immunological signals
• Integrity of the intestinal barrier (permeability and defense)
• Composition and diversity of the microbiota

Simply put: it's not just about "producing serotonin," but about in what biological context it's produced.

Microbiota and the gut-brain axis

The gut and the brain are connected by the gut-brain axis: a bidirectional communication network that integrates nervous, immunological, and metabolic signals.

This communication occurs, among other ways, through:

• The vagus nerve
• Immunological signals (inflammation, cytokines)
• Metabolites produced by the microbiota
• Hormones and neurotransmitters

When the microbiota is balanced, signaling tends to be more stable. When there is dysbiosis (imbalance), signals related to energy, appetite, rest, and stress tolerance can be altered.

Does more gut serotonin mean a better mood?

It's important to clarify here. Serotonin produced in the gut does not directly cross the blood-brain barrier into the brain.

So, why does it matter? Because gut balance influences variables that do impact how the nervous system is regulated:

• The availability of tryptophan for the brain
• Low-grade systemic inflammation
• The stress response and neuroendocrine signaling
• Metabolic stability (energy, appetite, satiety)

It's not about pursuing "more serotonin" as a number. It's about creating an internal environment where biological signals work towards balance.

Microbiota, inflammation, and emotional well-being

When the gut ecosystem loses diversity or becomes altered, inflammatory signals can increase, and the intestinal barrier can be compromised. This has chain effects: metabolism, the immune system, and the nervous system are interconnected.

That's why emotional well-being isn't just approached from the mind. It's also approached from the body. And, especially, from the root: the gut ecosystem.

Caring for the microbiota is caring for the system

At Andala, we don't look for "quick fixes" or simplistic messages. Caring for the microbiota is a fundamental, sustained, and realistic effort. Some levers that modulate the gut ecosystem:

• Dietary diversity (real variety throughout the week)
• Sufficient and well-tolerated fiber
• Polyphenols (fruits, vegetables, pure cocoa, EVOO, tea...)
• Rest and sleep regularity
• Stress management (because the axis is bidirectional)
• Daily movement
• Fewer ultra-processed foods (due to their impact on the ecosystem)