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Gut Check: The Neuroscience of How Your Gut and Brain Talk

Gut Check: The Neuroscience of How Your Gut and Brain Talk. What is real, what is hype.

A free, interactive neuroscience textbook for teens, patients, and families. What is real, what is hype.

Your gut has its own network of hundreds of millions of neurons, trillions of microbes, and a large share of your body's antibody-making cells, and all of them send signals to your brain. That conversation helps explain why stress can upset your stomach, why gut diseases so often travel with anxiety and depression, and why so many "heal your gut, fix your mind" posts sound convincing. Among adults with inflammatory bowel disease, about one in three report anxiety symptoms and about one in four report depression symptoms.1 In 2025, about one in three US high school students (33.3%) reported persistent feelings of sadness or hopelessness.2 This book teaches the real neuroscience behind the gut-brain connection, and it grades every popular claim for how strong the evidence actually is.

Hi, I'm Vee!

Vee the vagus nerve waving hello I'm a cartoon vagus nerve, the long nerve that carries messages between your gut and your brainstem. Most of my real-life fibers carry news up from the gut, so I hear a lot of gossip from down there. Let's check what the gut is really telling the brain!

Five ways your gut talks to your brain

The gut and brain stay in touch through several routes at once. Each one has its own chapter.

flowchart LR
    G["Gut wall<br/>(enteric nervous system)"]
    B["Brain"]
    G -- "1. Vagus nerve (Ch. 2)" --> B
    G -- "2. Spinal nerves: pain and stretch (Ch. 8)" --> B
    G -- "3. Gut hormones such as GLP-1 (Ch. 2)" --> B
    G -- "4. Immune messengers: cytokines (Ch. 4)" --> B
    G -- "5. Microbe-made chemicals such as short-chain fatty acids (Ch. 6)" --> B
    B -- "Stress hormones and nerve signals back down (Ch. 7)" --> G

The arrows run both ways, which is why stress can upset your stomach and a flare can change your mood. The strength of the evidence differs a lot between routes; the Hype Meter shows which links are solid in people and which come mostly from mice.

What makes this book different

  • The Hype Meter

    Every popular claim gets a visible grade: Strong, Moderate, Preliminary, or Hype. You'll always know whether a finding comes from mice or people, and whether it shows correlation or cause.

  • Hands-on simulations

    Every chapter has an interactive MicroSim. Build a wave of peristalsis, turn up the stress dial, amplify a pain signal, or run a fake probiotic trial and watch chance fool you.

  • The patient and family side

    Each chapter has an At the Bedside case that includes mood, stress, sleep, and school, plus sidebars for families and for teens living with a gut condition.

  • Free and open

    No account, no ads, no paywall. Licensed CC BY-NC-SA 4.0, works on a phone, and anyone can suggest a fix on GitHub.

Start here

What's inside
20 chapters in 5 parts From the gut's own nervous system to reading health claims like a scientist
20 interactive MicroSims Simulations you control, plus an interactive learning graph
Hype Meter grades On the most common gut-brain claims, from "90% of serotonin" to "leaky gut"
A case in every chapter Crohn's disease, IBS, celiac disease, Parkinson's disease, depression, and more
200 quiz questions Ten per chapter, each with an explanation
A learning graph 337 concepts mapped so you learn prerequisites first
Appendices A mock exam, a glossary, a teacher guide, a club kit, a pilot study kit, and a printable list of questions to ask your doctor

Part of a series

Gut Check is the second book by the same author. The first, From Neuron to Bedside, teaches how the brain works. This one teaches how the brain is wired to the rest of the body. You don't need to read the first book, but chapters link to it when a refresher helps.

Important

This book is for education only. It is not medical advice, and it cannot diagnose anything. The people in the cases, including Riya and Sam, are fictional. Never start, stop, or change a medicine, diet, or supplement because of something you read here; talk to your doctor. If you are in crisis, call or text 988 in the US.

Gut Check is an independent student project. It is not affiliated with or endorsed by any patient organization, hospital, university, or company.

  1. Barberio B, Zamani M, Black CJ, Savarino EV, Ford AC. (2021). Prevalence of symptoms of anxiety and depression in patients with inflammatory bowel disease: a systematic review and meta-analysis. The Lancet Gastroenterology & Hepatology, 6(5), 359-370. PubMed ↩

  2. Kiplagat SJ, Verlenden JV, et al. (2026). Unmet need for mental health counseling or therapy among US high school students with persistent sadness or hopelessness: Youth Risk Behavior Survey, United States, 2025. MMWR Supplements, 75(1), 35-43. CDC ↩