81. Dr. Zain Kassam: How Your Gut Bacteria Control Your Brain, Weight, and Longevity

Jul 29, 2025

Join Dr. Zain Kassam, a leading gastroenterologist and microbiome researcher, as he explores the fascinating world of gut health. He shares how your gut bacteria influence your mood, weight, and overall longevity, making them far from mere bystanders. Dive into the gut-brain connection, the surprisingly complex nature of probiotics, and the revolutionary potential of microbiome science. Kassam also discusses the impact of diet, fiber, and innovative therapies for conditions like IBS, highlighting the importance of personalized approaches to gut health.

Ask episode

AI Snips

Chapters

Transcript

Episode notes

ANECDOTE

Microbiome Meets Medicine

Dr. Zain Kassam met the microbiome through a patient with severe C. diff colitis.
A fecal transplant cured her quickly when antibiotics failed, showing the microbiome's power.

INSIGHT

Gut Microbiome as Invisible Organ

The human gut microbiome has more cells than the Milky Way has stars and acts like an invisible organ.
Gut bacteria affect digestion, immunity, mood, metabolism, and longevity, not just presence but active players.

ADVICE

Use Narrow Antibiotics Wisely

Always question if you truly need an antibiotic and seek narrow-spectrum options when possible.
Be vigilant about antibiotics' consequences to protect your beneficial gut bacteria.

Get the Snipd Podcast app to discover more snips from this episode

Get the app

What if I told you there's an organ in your body with more cells than the Milky Way has stars—and most doctors barely think about it? In this episode of Extend, I sit down with Dr. Zain Kassam, a gastroenterologist turned microbiome researcher who's pioneering how we understand the trillions of organisms living in and on us.

We dive into why your gut bacteria aren't just bystanders—they're actively producing molecules that affect your mood, metabolism, immune system, and even longevity. We also explore the gut-brain connection, why not all probiotics are created equal, and how the microbiome influences everything from depression to skin health.

Dr. Zain Kassam is a gastroenterologist, microbiome researcher, and Chief Medical Officer at Seed Health. He trained at McMaster University, Harvard, and MIT, where he pioneered clinical applications of microbiome science. He's led groundbreaking research on fecal transplants and develops evidence-based probiotic therapies.

We Also Discuss:

The Microbiome Revolution: From Forgotten to Life-Saving
Why Your Gut Has More Cells Than the Milky Way Has Stars
How Gut Bacteria Control Your Brain and Mood
The Butyrate Connection: Your Microbiome's Master Molecule
Why Most Probiotics Are Marketing Hype (And How to Choose Better)
The 4D Framework: Diversity, Delivery, Do-Gooders, and Data
Microbiome Testing: Crystal Ball or Expensive Guesswork?
From C. Diff to Cancer: When Gut Health Becomes Life or Death
The GLP-1 Secret: How Your Gut Makes Its Own Ozempic
Post-Antibiotic Recovery: Rebuilding After the Nuclear Bomb

Thank You for Our Sponsors:

Pendulum: Use code DARSHAN or use the link https://pendulumlife.com/discount/DARSHAN to get 20% off

IM8: Try IM8 today with a 30-day money back guarantee. You can get 20% off your first order with code DRSHAH at https://im8health.com/discount/DRSHAH.

Learn more about Dr. Shah:

Website: https://www.drshah.com/

Clinic: https://www.next-health.com/

Instagram: https://www.instagram.com/darshanshahmd/

Learn more about Dr. Zain Kassam:

X: https://x.com/DrZainSays/

Instagram: https://www.instagram.com/seed/

Get 25% off DS-01 with code EXTEND25 at Seed.com