How Fiber Shapes Your Gut — and Your Brain with Dr. Will Bulsiewicz

This one dietary shift can influence gut health, inflammation, and cognition. In this episode, Dr. Annie Fenn is joined by Will Bulsiewicz—known to many as Dr. B—to explore the powerful connection between the gut microbiome, inflammation, and brain health. Dr. B is a triple board-certified gastroenterologist, lifestyle medicine physician, and author of Fiber Fueled and Plant Powered Plus. They discuss why fiber is one of the most important—and most overlooked—nutrients for long-term health, how gut microbes produce anti-inflammatory compounds that influence the brain, and why plant diversity matters more than obsessing over specific nutrients. Annie and Dr. B also explore the gut barrier, chronic inflammation, the vagus nerve, and how modern habits like ultra-processed foods and alcohol may disrupt gut and immune health over time. This is part one of a two-part conversation focused on the gut-immune-brain connection and what everyday habits can do to support a healthier gut and brain. Chapters 00:00 Introduction to Dr. Will Bulsiewicz 02:45 Why fiber became the missing piece of modern health 06:44 What fiber actually does in the gut 09:21 Short-chain fatty acids and brain inflammation 10:18 Why some people struggle with fiber-rich foods 11:57 Beans, resistant starch, and rebuilding the microbiome 15:52 Plant diversity and the “30 plant rule” 18:23 Fiber supplements and filling the gaps 24:00 How quickly the gut microbiome can change 26:13 The gut barrier, immune system, and inflammation 32:36 The vagus nerve and gut-brain communication 35:28 Leaky gut, LPS, and chronic inflammation 38:53 Alcohol’s impact on the gut microbiome 44:16 Jenny & Annie’s Review and Do 47:24 Practical steps to support gut and brain health Links & Resources Dr. Will Bulsiewicz: https://theplantfedgut.com/ Plant Powered Plus: https://theplantfedgut.com/book/ Fiber Fueled: https://theplantfedgut.com/fiber-fueled/ 38TERA: https://38tera.com/ Brain Health Kitchen Substack: https://brainhealthkitchen.substack.com/ Better Brain: https://betterbrain.com/annie NeuroReserve: https://neuroreserve.com Code: BHKPodcast