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About This Book

Why does this book exist?

Vee the vagus nerve Because a teen living with a gut condition, or anyone scrolling past "heal your gut" posts, deserves a clear, honest, free explanation of how the gut and brain actually talk.

The problem

The gut-brain connection is everywhere online, and much of it is oversold. Real research shows that the gut's own nervous system, the vagus nerve, gut microbes, and the immune system all send signals to the brain. But many claims built on that research go far beyond it, often to sell a supplement, a test kit, or a diet.

Teens with gut conditions rarely get the science explained. Inflammatory bowel disease, IBS, and celiac disease often travel with stress, pain, anxiety, and low mood. Patient guides are helpful but short, and research books are written for graduate students and cost money.

I could not find a free, textbook-length, high-school-level, interactive book on the neuroscience of the gut-brain axis. General textbooks teach digestion and the nervous system in separate chapters. Searching is not proof that nothing exists, so if you know of one, please tell me.

What this book does

  • Grades the evidence. Every popular claim gets a Hype Meter grade, and every study is labeled as mouse or human, correlation or cause.
  • Explains the idea before the vocabulary. Every new idea starts with an everyday comparison.
  • Lets you try things. Every chapter has an interactive simulation, with a note on what the model leaves out.
  • Includes the patient and family side. Every chapter has a fictional case that covers mood, stress, sleep, and school, plus sidebars for families and for teens living with a gut condition.
  • Gives you practice. Every chapter has a Your Gut Check section, exercises at every level of Bloom's Taxonomy, and a quiz.
  • Stays free. It's licensed CC BY-NC-SA 4.0 and hosted on GitHub Pages.

Who it's for

  • High school students (grades 9 to 12) curious about the brain, the body, and medicine
  • Teens living with Crohn's disease, ulcerative colitis, IBS, celiac disease, or stress-related gut symptoms
  • Parents, siblings, and friends who want to understand (see For Families)
  • Teachers running a biology, health, or neuroscience unit or club (see For Teachers)

The only prerequisite is one year of high school biology.

About the author

Aaryav Sharma (ORCID 0009-0006-3333-0809) is a high school student in Minnesota who plans to study neuroscience and medicine. He also wrote From Neuron to Bedside, a free interactive neuroscience textbook. A close family member lives with ulcerative colitis, which is a big part of why this book exists.

How this book was made, and how AI was used

I chose the topic, set the structure and the rules for every chapter, and decided how the book would grade evidence. I used Claude Code and Dan McCreary's open-source intelligent-textbook skills to help research, draft text, and build the simulations, and to run several separate rounds of fact-checking and editing.

Because AI helped write this book, mistakes are possible, and accuracy matters a lot in a book about health. The Accuracy and Corrections page explains how the book is checked and lists every fix. If you find an error, please tell me through the Contact page.

Acknowledgements

Disclaimers

  • This book is for education only. It is not medical advice and cannot diagnose any condition. Talk to a doctor about symptoms, treatments, diets, or supplements.
  • The people in the cases, including Riya, Sam, and Leo, are fictional composites.
  • Gut Check is an independent student project. It is not affiliated with or endorsed by any patient organization, hospital, university, or company.