158 : IBS, finding and treating the root cause of irritable bowel syndrome

Dr. Jenn Simmons speaks with pharmacist turned integrative health author Dr. Isabella Wentz about the hidden drivers of IBS, why so many people get mislabeled without answers, and how gut issues can connect to autoimmune disease, hormones, and chronic inflammation. Dr. Wentz shares her own path from conventional pharmacy into root-cause medicine, including how her personal experience with fatigue, IBS, and Hashimoto’s changed everything.We discuss the limits of standard IBS care, the most useful testing strategies, and the major causes she sees in practice, from SIBO and food sensitivities to protozoal infections and hormone disruption. This conversation is especially useful for anyone who has been told their digestive symptoms are “just IBS” and wants a more complete framework. Key topics Dr. Wentz shares how she entered pharmacy school wanting to invent drugs, not practice natural medicine, and how her own illness redirected her career. Her first major gut issue began in pharmacy school with fatigue and severe IBS symptoms, which improved after removing certain soy-based meal replacements. She explains IBS as a wastebasket diagnosis, not a true root-cause diagnosis, and says it often reflects a much bigger underlying problem. She notes that IBS can precede autoimmune conditions by 5 to 10 years, which is why gut symptoms should be taken seriously. She outlines red flags that should prompt further testing, including rectal bleeding, blood in stool, weight loss, fever, and new IBS symptoms after age 35 to 40. She recommends functional testing such as SIBO breath testing and comprehensive stool analysis like GI Map or Gut Zoomer to look for dysbiosis, low enzymes, and infections. She explains why SIBO often comes back if the true driver is not addressed, such as low thyroid function, low stomach acid, H. pylori, or protozoal infection. She cautions against overly restrictive diets, saying many people end up with “gluten-free junk food” patterns or elimination diets so strict they create new problems. She discusses food sensitivity testing, saying results vary widely by method, but she has seen strong practical value in IgG testing for symptom tracking. She highlights the role of parasites and protozoa, especially microscopic organisms like Giardia and Blastocystis, and her preference for testing rather than guessing. She and Dr. Simmons discuss hormone effects on digestion, including how progesterone decline and estrogen dominance may contribute to constipation and IBS symptoms. Dr. Wentz emphasizes that healing should support real life, not perfection, so people can travel, eat normally sometimes, and still feel well. Timestamps 00:00 - Why Dr. Wentz wrote her fifth book on IBS 03:29 - From pharmacy school to the first signs something was wrong 04:42 - Fatigue, IBS, and the soy lecithin discovery 06:57 - When Hashimoto’s changed the entire direction of her career 08:21 - Why root-cause medicine became impossible to ignore 10:51 - How she found answers before functional medicine was mainstream 13:54 - Why IBS is often the wrong label for the real problem 18:39 - Red flags that should never be written off as IBS 21:26 - The two tests she relies on most: SIBO and stool analysis 23:15 - Why SIBO keeps returning when the root cause remains 26:53 - Protozoa, infections, and why SIBO is often secondary 28:18 - Movement, walking, and improving gut motility 29:06 - What IBS still gets wrong today 30:17 - Why gluten and dairy are often the first foods to remove 31:33 - When elimination diets become too extreme 33:30 - Processed “healthy” foods, artificial sweeteners, and gut irritation 36:27 - Birth control, IBS risk, and hidden hormone effects 42:26 - Progesterone, estrogen dominance, and constipation cycles 45:04 - Gut con