Show notes
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 Thank you to our sponsors! - Butcher Box | Go to ButcherBox.com/HUMANUPGRADE to get $20 off your first box, plus your choice of free ground beef for life, or free chicken thigh - Download Dave’s Free Peptide Guide at daveasprey.com/peptide-guide. - Caldera + Lab | Go to calroy.com/dave for the research, a discount, and a 45-day money back guarantee. - Kenetik | Instead of pushing your system harder, Kenetik feeds your brain the ketones it craves to fuel calm clarity and steady focus. Go to drinkkenetik.com/DAVE and use code DAVE for a discount. 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 • Get My 2026 Clean Nicotine Roadmap | Enroll for free at https://daveasprey.com/2026-clean-nicotine-roadmap/ • Dave Asprey's Latest News | Go to https://daveasprey.com/ to join Inside Track today. • Danger Coffee: https://dangercoffee.com/discount/dave15? • My Daily Supplements: SuppGrade Labs (15% Off) • Favorite Blue Light Blocking Glasses: TrueDark (15% Off) 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 See Privacy Policy at https://art19.com/privacy and California Privacy Notice at https://art19.com/privacy#do-not-sell-my-info.