Podcast Summary: The Human Upgrade — How Gravity Shapes Your Body, Brain, and Health (Ep. 1338)

Host: Dave Asprey
Guest: Dr. Brennan Spiegel (Professor of Medicine & Public Health, Cedars-Sinai/UCLA)
Date: October 2, 2025

Episode Overview

In this episode, Dave Asprey explores gravity as a fundamental and often ignored force that constantly impacts our biology, mental state, and health. Guest Dr. Brennan Spiegel, author of the new book Pull: How Gravity Shapes Your Body, Steadies the Mind, and Guides Your Health, breaks down how gravity underpins nearly every aspect of human physiology—from our musculoskeletal systems to consciousness itself. The duo connect gravity not just to obvious issues like bone health, but also to topics like depression, serotonin production, gut function, and even the challenges of space travel.

Key Discussion Points & Insights

1. Gravity: The Hidden Variable in Health and Biohacking

• Asprey positions gravity as the “missing link” in biohacking, overshadowed by more talked-about variables like light, sound, food, or vibration.

  "Gravity is one of...the most ignored of all of the signals because it's always present and we just assume it's there." — Dave Asprey (03:01)

• Dr. Spiegel describes humans as “fish in water,” so well-adapted to gravity we forget it’s there—yet every organ, system, and cell is shaped to resist it.
• Evolution made us bipedal, which changed how gravity stresses the spine, viscera, and connective tissues. Back pain, chronic pain, and even emotional states often signify “gravity intolerance” (04:45–06:30).

2. How Medicine Overlooks Gravity

• Medicine studies organs in isolation, ignoring the shared goal of withstanding gravity to keep fluids moving and brains oxygenated:

  "Physics came first and biology second. Nowhere in medical school did I hear that we came out of the Earth...and evolved all these pumps and tubes to keep the hydraulics so you can stay awake." — Dr. Spiegel (06:32)

• Low blood pressure, dizziness, ankle swelling, and even depression/anxiety are recast as symptoms of poor “gravity management.” (07:14–07:36)

3. Physiology and Structure: Musculoskeletal, Fascia, and Interstitium

• Chronic pain, especially low back pain, is reframed as a form of gravity intolerance.

  "It's a way of your body telling you you're literally not aligned with this downward pull...of the planet." — Dr. Spiegel (09:48)

• Fascial and interstitial tissue (the connective “in-between” spaces recently recognized as their own functional organ) play a huge role. Disease often starts at connection points (“seams”), which must be resilient against gravity (11:32–12:54).
• Ancient Chinese systems like qigong/nigong directly train this interstitial strength, even if with different terminology.

4. Practical Experimentation: Weighted Vests & Proprioception

• Spiegel describes wearing a weighted vest plus 20 lb. ankle weights for 8 weeks to challenge his gravity management systems (13:09–14:40).

  “At first it was exhausting, but...I found this strength from within...much stronger in my interscapular space, the fascia, the tendons. I realized I was standing up, much straighter.” — Dr. Spiegel (14:26)

• Both Asprey and Spiegel point to the importance of proprioceptors and “graviception”—the body and brain’s dynamic sense of gravity, integrated in regions like the anterior insula (15:41–16:42).
• Use of balance boards and micro-movements at work amplify these proprioceptive and graviceptive systems.

5. Gravity in Space, Airplanes, and Microbiome

Space/Air Travel:

• In space, fluid redistribution causes vision loss, cognitive issues, and mitochondrial/microbiome dysregulation for astronauts (21:31–23:17).
• Atmospheric pressure, not just gravity, matters during air travel—high altitude or airplane cabins stretch internal organs and can affect gut/brain health (23:17–24:07).
• Practical tips while flying:
  • Use of compression gear (tights, shirts) can restore some of the “pressure” absent at altitude (24:21).
  • Hydration, sodium-based electrolytes, and dietary adjustments help maintain gravitational and pressure homeostasis (25:42–27:16).

Microbiome:

• Gravity, motion, and microbiome diversity are deeply intertwined. Both humans and gut microbes co-evolved with gravity, and healthy serotonin production (which is gravity-linked) depends on the microbiome (27:58–29:10).

6. Gravity and Serotonin: The Chemistry of Uprightness

• 95% of serotonin is produced in the gut, not the brain. Serotonin primes pumps and tubes, aids vascular tone, and calibrates blood pressure, baroreceptor reflexes, and even inner ear function (29:40–31:18).
• Without serotonin: "You would be a flaccid sac right now." Babies can't move because they lack serotonin and a mature microbiome.
• Psychologically, upward movement represents “elevation” (happiness/high), and downward movement or “being pulled down” correlates with depression—both linguistically and biologically (31:35–32:24).
• Even antidepressants/psychedelics (“gravity drugs”) create the phenomenology of lightness or floating.

7. Disease as Gravity Intolerance

• Orthostatic disorders like POTS and symptoms such as lightheadedness, GI issues, and even chronic diseases are connected to collagen structure, membrane “seams,” and gravity (32:55–34:32).
• “Leaky gut” and many systemic diseases arise where bodily systems connect, especially if those are gravity-stressed (34:17–35:18).

8. Movement, Grounding, and Gravity Training

• Barefoot or minimal footwear builds the gravity management surfaces of the foot, improving fascia and full-body alignment (36:53–38:39).

  "Gravity management begins with the feet." — Dr. Spiegel (37:39)

• Techniques like the Alexander technique trace back healing voice/breath/posture issues to gravity alignment.

9. Sleep, Elevation, and Circadian Gravitational Effects

• Elevating the head of the bed, acid reflux, and glymphatic brain clearance are perspectives through which sleep’s gravitational aspects are examined (40:44–43:09).
• Historical evolution from sleeping in trees to ground sleeping may have had a gravity-related impact on human intelligence (42:22–43:09).
• Hospitalization: Keeping patients flat is shown to have consequences; movement and uprightness are needed for optimal health and recovery.

10. Gut Disease and Gravity

• Crohn's disease, IBS, and other GI issues can be exacerbated by altitude and minor gravity changes (44:48–45:40).
• Disease prevalence changes by latitude and altitude, possibly due to tiny differences in gravitational force—an underexplored area.

11. Vagus Nerve, HRV, and Gravity

• HRV (heart rate variability) is reframed as a “gravitational fitness” metric because of the interplay between respiratory and cardiac pumps, both managed in relation to gravity (46:03–48:49).
• Vagus nerve stimulation can affect serotonin release and manage GI/mental health through gravitational effects.

12. Piezoelectricity and Gravity Sensing

• All cells, especially membranes and bones, are piezoelectric (convert mechanical movement to electric signals).

  “Piezo channels...take gravity and convert it into electromagnetism in the body.” — Dr. Spiegel (49:57–50:19)

• Well-functioning piezo channels let the body sense “the map of the world,” turning gravitational data into nervous system signals.

13. A Gravity-Centric View of Human Reality

• Dr. Spiegel positions gravity as the ultimate frame, encouraging biohackers and clinicians alike to consider the gravity-electromagnetism axis in understanding and designing health interventions (51:30–52:24).

14. Obesity, Depression, and Mental Gravity

• Obesity increases effective gravity on tissue, making movement, circulation, and mood worse—“depression and obesity are gravity illnesses” (53:08–55:52).

  “If you feel like you’re on a planet that’s pulling you down, you can’t get up out of bed, you’re exhausted, those are the symptoms of depression...those are also the symptoms of too much gravity. It’s one and the same.” — Dr. Spiegel (54:41)

15. Training Gravity Intolerance and Benefits of Functional Movement

• Rucking, dead hangs, balance training, band resistance, and micro-movements all improve gravity management (56:06–59:53).
• Standing on one leg for 10 seconds is a powerful combined metric of gravity tolerance (58:12).
• Flotation therapy (float tanks) can alter not just sensation of weight and time, but possibly consciousness and flow states (56:57–57:49).

Notable Quotes & Timestamps

• On Gravity as Biohacking’s Blind Spot:

  "Gravity is the most ignored of all signals because it's always present and we just assume it's there."
  — Dave Asprey (03:01)

• On the Role of Serotonin:

  “Without [serotonin], you would be a flaccid sac right now.”
  — Dr. Spiegel (29:45)

• On Depression and Gravity:

  "If you feel like you’re on a planet that’s pulling you down...those are the symptoms of depression. Those are also the symptoms of too much gravity."
  — Dr. Spiegel (54:41)

• On Movement and Posture:

  "Gravity management begins with the feet."
  — Dr. Spiegel (37:39)

• On Changing How We See Health:

  “Piezo channels...take gravity and convert it into electromagnetism in the body.”
  — Dr. Spiegel (50:19)

• On Biohacking and Gravity’s Centrality:

  "It's literally a fundamental force of physics..."
  — Dr. Spiegel (52:21)

Timestamps for Key Segments

• 04:01 — Gravity’s role in shaping our biology/evolution
• 11:32 — Fascia, tensegrity, and “seam resilience”
• 13:09–14:46 — Spiegel’s weighted vest experiment
• 15:41 — Graviception and the brain’s anterior insula
• 21:31 — Gravity’s effects on astronauts and in airplanes
• 29:23–31:18 — Serotonin as a gravity management molecule
• 36:53–38:39 — Barefoot/minimal footwear and foot mechanics
• 42:22–43:09 — Gravity, sleep, and human evolution
• 46:03–48:49 — Vagus nerve, HRV, and gravity
• 49:36–51:09 — Piezoelectric membranes: gravity-to-electromagnetism translation
• 53:08–55:52 — Obesity and depression as gravity diseases
• 56:06–59:53 — Balance, micro-movements, and testing gravity resilience

Memorable Moments

• The reframing of common illnesses, depression, and obesity as “gravity intolerance” is novel and memorable.
• The idea that “being high” with psychedelics or antidepressants is literally an experience of altered gravity/serotonin.
• Asprey’s and Spiegel’s mutual nerding out about vibrant five-finger shoes, float tanks, and anti-gravity machinery bring the abstract back to practical and accessible biohacking tips.
• The connection between piezoelectricity and fundamental sensory data is a paradigm shift in understanding how the body translates physical forces into biological response.

Final Thoughts

This episode positions gravity as a foundational pillar in health, far broader in scope than its roles in bone density or basic movement. Dr. Spiegel’s insights invite us to reconsider everything from our mental health, posture, footwear, and microbiome, to how we should train, treat disease, and even design environments for healing and optimal performance. If you’ve never considered gravity as a crucial input to hack, this conversation may be your launch point.

Book Mentioned:
Pull: How Gravity Shapes Your Body, Steadies the Mind, and Guides Your Health by Dr. Brennan Spiegel

For more resources and the full episode, visit The Human Upgrade with Dave Asprey.