Dr Brennan Spiegel (physician, gastroenterologist, and author of Pull) and Dr Lachlan Kent (cognitive scientist and founder of Mental Gravity) explore serotonin as a gravity-management molecule, reframing it not simply as a “happiness chemical,” but as a fundamental biological system that allows life to stand up, move fluids, regulate balance, and remain psychologically buoyant in a gravitational field.

Together, Brennan and Lachlan unpack new research on serotonin’s role across the gut, cardiovascular system, lymphatics, vestibular system, reproduction, and mood—showing how 95% of serotonin is produced in the gut, in symbiosis with the microbiome. They trace serotonin’s evolutionary origins from ocean life to land, altitude, and even space, and discuss practical implications for diet, exercise, sunlight, microbiome care, and mental health.

1. What Is Serotonin?

A whole-body gravity resilience molecule, not just a brainneurotransmitter

Exists in two largely separate compartments: brain and gut
Central to movement, circulation, balance, mood, and vitality
Evolutionarily conserved across plants, animals, and humans

Serotonin as a Gravity-Management System

Gut & DigestionMotility against gravity in any body orientation

Pumps & Tubes
Blood pressure regulation, cardiac contractility, lymphatic return

Balance& OrientationVestibular function; dizziness during SSRI withdrawal

Reproduction
Retrograde uterine contractions that move sperm upward against gravity

Mood &Energy
Mental elevation, vitality, resilience, and time perception

The Microbiome–Serotonin Alliance

Trillionsof microbes are required to trigger serotonin production
The gut as a “dark, sulfurous, hydrothermal” evolutionary niche
A symbiotic bargain: microbes get mobility; humans get serotonin
Changes in altitude, microgravity, and spaceflight rapidly alter serotoninbiology

STACK TEN: The Anti-Gravity Diet (introduced)

A practical framework from Pull for supporting serotonin production via tryptophan-rich foods.

Core principles:Tryptophan as substrateMicrobiome diversityDietary balance rather than supplementation alone

Therapeutic & Self-Care Implications

Dietary modification (tryptophan-rich foods, microbiome-supportive diets)Exercise and movementSunlight and time outdoorsWorking with dietitians for GI and mood conditions (e.g., low-FODMAP when indicated)Understanding limits and side effects of SSRIsNaturally supporting serotonin across body and mind

Metaphor & Meaning

The gutmicrobiome as the “spice factory” of human biologySerotonin as the true “spice of life”—powerful, regulating, and double-edgedGravity as the organizing principle linking biology, psychology, and medicine

Timecodes

00:00 —Welcome & why serotonin matters
01:10 — Serotonin beyond the “happiness chemical”
02:20 — Gut vs brain serotonin compartments
03:20 — Pumps, tubes & whole-body effects
04:25 — Lymphatics, reproduction & balance
06:20 — Evolutionary origins & gravitation
08:10 — Microbiome symbiosis metaphor
10:15 — Altitude, spaceflight & serotonin disruption
11:30 — STACK TEN diet introduced
12:45 — Diet, microbiome & mood disorders
13:50 — Dune, spice & serotonin metaphor
15:45 — SSRIs: benefits, limits & side effects
17:00 — Natural serotonin support & integration
17:45 — Closing reflections & next steps

Resources

The Gravity Doctors website: https://thegravitydoctors.com
Dr Brennan Spiegel: https://brennanspiegelmd.com
Dr Lachlan Kent: https://lachlankent.au
Book — Pull: How Gravity Shapes Your Body, Steadies the Mind, and Guides Our Health