Fix your gut.
I had IBS for years before I understood what was actually wrong with me. This is the guide I wish I'd had back then.
It follows a meal from your mouth right through to the other end, covers every system that controls the journey, and works through the common things that go wrong: IBS, SIBO, coeliac, IBD, food intolerances, constipation, and all the rest. Every claim is weighted by how strong the evidence behind it actually is.
Delivered as a PDF, readable on any device.
Written and referenced by me.
Four things you've probably been told about your gut.
Each one of these has a grain of truth in it that's been stretched way past what the research actually supports. The guide works through all four properly (and more), backed up by the supporting science.
"90% of your serotonin is made in your gut, so your gut determines your mood."
The verdictMost of your serotonin is made in your gut, but this is almost entirely misinterpreted by most people. The serotonin made in your gut never reaches your brain, and the job it's actually doing down there is a completely different one.
"Your gut is your second brain."
The verdictYour gut essentially has its own autonomous nervous system of around 200 million neurons, and it can digest a meal with the brain disconnected entirely. That is incredible. But the "second brain" nickname is overselling it.
"Leaky gut is behind your fatigue, your brain fog and your autoimmune disease."
The verdictIncreased permeability is real and measurable, but on its own it rarely produces disease. Plenty of people have increased permeability and never develop a problem. But a strong gut barrier still matters, and I cover that thoroughly in the guide.
"Send off a stool sample and you'll find out what your microbiome needs."
The verdictResearchers have tested these companies: they posted them identical portions of a single stool sample, but the results they got back from each company were entirely different.
The guide works this way throughout. Where the evidence is strong, I tell you it's strong. Where a finding comes from mice, or from a trial of ten people with no control group, I tell you that too. I absolutely believe there's value in anecdotal evidence and mechanistic speculation ("bro-science"), but we have to acknowledge where evidence isn't as strong.
Follow a meal from one end of the gut to the other.
The guide is built around the route your food takes through the digestive system. Each stage gets its own chapter covering how it works, what goes wrong with it, and what you can do about that.
The mouth
Digestion starts well before you swallow. Your mouth primes your entire digestive tract through the vagus nerve, and it houses the second most diverse microbial community in your body, with consequences almost nobody thinks to trace back to their mouth.
The stomach
Stomach acid does three non-negotiable jobs, and suppressing stomach acid will cost you all three. I go through acid reflux, including why the standard reflux drugs ease the symptom but leave the root causes completely untouched.
The small intestine
Almost everything you eat is absorbed here in the small intestine, across a lining one cell thick that rebuilds itself every few days. This chapter covers how each macronutrient crosses into your blood, and the specific points where iron and B12 absorption fail.
The colon
The colon reclaims nearly all the fluid that reaches it, and it's the one major tissue in your body that has evolved to run on a bacterial metabolite rather than on glucose. The microbiome chapters are located in this section, the longest part of the guide.
Stool and defecation
The final stage. What your stool looks like and how long it took to get there are two of the most useful diagnostics available to you, and both are free.
Those five stages are the spine of this guide.
Eight systems controlling the gut.
These decide how well every stage of the journey works. Each one gets its own chapter.
The gut barrier
Four layers stand between your gut contents and your bloodstream. The chapter sets out exactly what damages each layer, and what rebuilds it.
The microbiome
Which species matter and why microbial diversity is something you want.
Bacterial metabolites
Your bacteria produce compounds that reach your liver, arteries and brain. Many of them help you, some don't.
Fibre
There are 4 different main types of fibre doing four different jobs. Total grams of fibre per day tells you very little on its own.
Motility
What moves food along, the housekeeping wave that sweeps the gut between meals, and what happens when motility stops working properly.
The gut immune system
The gut is where the majority of your body's immune system is located, It decides thousands of times a day what to tolerate and what to attack.
The gut-brain axis
Five real communication routes between the gut and the brain, and what each of them can and cannot do.
Circadian rhythm
The same meal is handled differently at 8am and at 10pm. Your gut and your microbiome both operate on a biological clock.
11 gut disorders.
Most gut advice stops at general principles. This guide works through the specific conditions one at a time: what each one is, how it's properly diagnosed, and the evidence-supported practices for managing it.
Irritable bowel syndrome
Recurring abdominal pain tied to your bowel movements, with nothing visible on a scan or a scope. IBS is the most common gut disorder in the world, and the most frequently misunderstood.
SIBO
Bloating and distension that start high up and early, because bacteria are fermenting your food before you've finished absorbing it. SIBO is almost always downstream of something else.
Coeliac disease
An immune attack on your own intestinal lining, triggered by gluten. Close to 1 in 100 people have it, and many of them have no idea.
Inflammatory bowel disease
Crohn's and ulcerative colitis. These involve real, visible destruction of the gut wall - this is the one condition in this guide where the wellness industry's typical approach can become genuinely dangerous.
Lactose intolerance
Declining lactase, and undigested milk sugar reaching your colon. Lactose intolerance is frequently secondary to some other problem, which also means it's often reversible.
Fructose malabsorption
This is caused by a transport limit rather than a missing enzyme. Fructose malabsorption is present to some degree in at least a third of people, and it's strongly dose-dependent.
Histamine intolerance
Headaches, flushing, hives and gut upset from aged, cured and fermented foods. This is a sneaky issue that often hides under the radar.
Non-coeliac gluten sensitivity
Around 10% of people report having this. But when tested properly under blinded conditions, the culprit usually turns out to be something other than gluten itself.
Chronic constipation
Three distinct types needing three different fixes, and the one that gets missed most often isn't a problem with the colon at all.
Functional diarrhoea
Chronic loose stools without the pain that defines IBS-D. One common cause is missed constantly, and the treatment for it works dramatically well.
Diverticular disease
Small pouches bulging through the colon wall. A third of people have them by 60, and the standard advice about what to avoid has been formally overturned.
Recognise yourself in any of these?
Each one gets a full section: what it is, how it's properly diagnosed, and what the evidence actually supports in terms of treatment and management.
Get the Guide — R$ 173,00You should be able to see how firm the ground is.
Gut science moves quickly and a great deal of it is still early. Most of what you read online is cell studies, mouse studies, or pure mechanistic speculation.
I've tried to make the strength of evidence clear throughout this guide, so you know which claims you can most put your trust in.
Every recommendation is graded
The tables carry a strength-of-evidence rating alongside each intervention, so you can see which ones rest on solid human trials and which are promising but thin.
Mouse studies are labelled as mouse studies
A lot of microbiome research is done in rodents, and rodent guts differ from ours in ways that matter. Where a finding hasn't been demonstrated in humans, the text says so.
Weaknesses and conflicts are stated
Where a trial ran without a control group, or an author held equity in the company funding it, that's stated in the text right next to the finding.
273 scientific references
There's a full bibliography at the end with DOIs, so you can go and read any of the studies for yourself rather than taking my word for it.
Who this is for
Buy this guide if
- You've had gut symptoms for a while and you want to understand what's actually driving them before you try another protocol.
- Your gut is fine and you'd like to keep it that way.
- You want the physiology explained properly, rather than a list of rules to follow blindly.
- You've been handed contradictory advice about fibre, dairy, gluten or meat, and you want to know what's true.
- You'd rather know how strong the evidence behind a recommendation is than be told "trust me bro".
Don't buy it if
- You have red flag symptoms: blood in the stool, unintentional weight loss, a persistent change in bowel habit. Those need a doctor.
- You're looking for a natural alternative to medical treatment for inflammatory bowel disease. I'm explicit in the guide that IBD needs a gastroenterologist.
- You want a quick fix protocol with no explanation attached to it.
- You're hoping the answer is a supplement stack.
Before you decide.
How is this different from the gut health section in your Complete Nutrition Guide?
This guide started out as that small section but it kept growing until it was obvious it needed to be its own book, so here it is. My Complete Nutrition Guide gives you the overview of gut health as part of a much wider picture. This is the full treatment.
Do I need to have a gut problem to get anything out of it?
No. Well over half of the guide is about how a healthy gut works and what keeps it healthy. The disorders section is there for the people who need it, and the rest is there whether you have symptoms or not.
How technical is it? Do I need a science background?
No background needed. I build the mechanisms up from the ground and define the technical terms as they come up. It is detailed though. This is a book to work through rather than a quick-reference sheet.
Is it a diet plan?
No. There's a practical guidelines chapter at the end that tells you what to actually do, but most of the guide is spent explaining why, so you can make your own decisions instead of following someone else's rules just on trust.
Will it tell me what's wrong with me?
It will help you narrow it down a lot, and it will tell you which tests are worth asking for. But it's not a clinical diagnosis tool. For anything on the red flag list, see a doctor.
Does it cover the fibre and carnivore argument?
At length. I go through why some people genuinely feel better after cutting out plants, and what's usually going on underneath when that happens.
What do I get, and how quickly?
A 124-page PDF that's available to download the moment you order, with the link emailed to you as well. It reads fine on a phone, a tablet or a laptop.
The gut isn't one thing so there's no "one-size-fits-all" answer.
It's a barrier, an ecosystem, a nervous system, an immune organ and a chemical reactor, all in constant conversation with each other and with the rest of your body. No single supplement can fix the whole thing. Understanding it properly is a different matter.
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Written, researched and referenced by Ben Winney.