Dr. Karan Rajan on Fiber Fermentation, Sodium Myths, and What Your Poop Reveals About Disease Risk

Your poop is more predictive than almost any other health signal, and you are flushing that data away every single day without a second look.

Watch this episode on YouTube for the full video experience:

https://www.youtube.com/@DaveAspreyBPR

Host Dave Asprey sits down with Dr. Karan Rajan, a practicing NHS gastrointestinal surgeon, best-selling author, and Chief Science Officer at Throne, who has built a following of over 12 million people by making gut science accessible and actionable. He has spent his career removing colon cancers, treating digestive disease, and now studies how gut bacteria drive nearly every system in the body, from hormone metabolism to brain optimization.

They break down why fibermaxxing can backfire without the right mix of fast, medium, and slow fermenting fibers, and why generic "eat more fiber" advice ignores what your gut bacteria actually need. The conversation covers protein absorption limits and how much your body can really use, the truth about saturated fat and metabolism, and why the sodium-to-potassium ratio matters more than sodium alone. They also dig into fasting and the gut's natural cleaning cycle, the estrobolome and testobolome and their role in hormone balance and longevity, and how AI is starting to reshape personalized health data, supplements, and functional medicine. Dr. Rajan shares some of the strangest objects he has surgically removed from patients, and explains what your poop's color, shape, and consistency reveal about liver function, inflammation, and disease risk long before symptoms show up anywhere else.

This is essential listening for anyone serious about biohacking, gut health, human performance, longevity, mitochondria function, nootropics, ketosis, carnivore and fiber-based diets, sleep optimization, anti-aging, and hacking your metabolism from the inside out.

You'll Learn:

Why fibermaxxing can cause bloating instead of better gut health
The real difference between fast, medium, and slow fermenting fibers
How much protein your gut can actually absorb and digest
Why low sodium may be more dangerous than high sodium for most people
How fasting triggers your gut's natural cleaning cycle, the migrating motor complex
What your poop's color and consistency can reveal about liver and metabolic health
How gut bacteria influence hormone metabolism through the estrobolome and testobolome
Where AI and functional medicine are headed in personalized gut health tracking

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Dave Asprey is a four-time New York Times bestselling author, founder of Bulletproof Coffee, and the father of biohacking. With over 1,000 interviews and 1 million monthly listeners, The Human Upgrade brings you the knowledge to take control of your biology, extend your longevity, and optimize every system in your body and mind. Each episode delivers cutting-edge insights inhealth, performance, neuroscience, supplements, nutrition, biohacking, emotional intelligence, and conscious living.

New episodes are released every Tuesday, Thursday, Friday, and Sunday (BONUS). Dave asks the questions no one else will and gives you real tools to become stronger, smarter, and more resilient.

Keywords: Karan Rajan, gut surgeon, fibermaxxing, gut microbiome, Bristol stool chart, poop health, Throne, fermentation geography, soluble fiber, insoluble fiber, prebiotics, inulin, oxalates, estrobolome, testobolome, migrating motor complex, sodium potassium ratio, saturated fat, ghee, collagen, protein absorption, keto, carnivore, fasting, gut bacteria, flatulence science

Resources:

• Dr. Karan's Newsletter: https://drkaran.kit.com

• Check Out Dr. Karan’s YouTube: https://www.youtube.com/c/DrKaran

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Timestamps:

00:00 – Trailer

00:55 – Meet Dr. Karan Rajan

04:04 – Kellogg's History & Farts

11:53 – Throne Poop Tracking

19:35 – Poop Colors & Wild Stories

28:02 – Worst Foods & Saturated Fat

36:26 – Fiber Fermentation Geography

46:57 – Sodium & Salt Myths

59:03 – Keto, Carnivore & Fasting

01:04:45 – AI, Misinformation & Closing

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Everything You Need To Know About Your Poop | Gut Surgeon Explains : 1533

The Human Upgrade: Biohacking for Longevity & Performance

Everything You Need To Know About Your Poop | Gut Surgeon Explains : 1533