What Is Leaky Gut? Symptoms, Causes and What I Start With
Roughly 70 to 80 percent of your immune system sits in and around your gut. I quoted that figure on the show, and it is the reason a gut lining that lets the wrong things through can be connected to more than a bloated stomach: skin flare-ups and brain fog can sit on the same list. Leaky gut is the everyday name for a lining whose tight junctions have loosened, and when clients bring me this picture, the first moves are sleep and stress, followed by a structured way of eating. Supplements and testing come after.
This is part two of my gut series on the Talking Nutrition podcast, episode 211, recorded solo. It follows part one on low stomach acid. Everything here is education and does not replace medical advice.
What Is Leaky Gut and Why Does the Gut Lining Matter?
Start with the word itself. On the show I said, "I don't even believe the medical field recognises this term as an official thing." The research name is intestinal permeability, and it remains an area of developing research. I use leaky gut as a lay shorthand for what I see with clients, and I hold it loosely.
Here is the picture I use:
I want you to think of your gut lining as a protective layer between your food, microbiota, and then your bloodstream.
Think of a security gate with selective entry. Nutrients hold the right pass and walk through. Toxins and undigested food proteins stay on the gut side. The gate is made of tight junctions, small connections between the cells of the lining, and they are built to open selectively. "That's the whole point of a security gate," I said. When those junctions loosen, particles that were meant to stay inside can reach the bloodstream, and the immune system treats them as invaders. Inflammation can follow.
Why Does a Loose Gut Lining Reach Beyond Digestion?
Because the immune system lives there. I gave the 70 to 80 percent figure, and I added that roughly 90 percent of serotonin is made in the gut, which is one reason mood and gut can be connected. So when a client lists fatigue and joint pain, I at least ask whether the gut is one of the factors. It is one lens, and plenty of other things can sit behind those symptoms.
The thyroid is where I see this most. With Hashimoto's I think about three pieces: genetics, triggers and intestinal permeability. In the clients I have worked with, the gut has been a big component, which is why I like to look at TPO antibodies on a blood panel alongside gut health. Reading that panel is a conversation for your doctor. I wrote more in my post on Hashimoto's disease.
If you would rather hear me talk it through, the full episode is right here.
Which Leaky Gut Symptoms Do I See in Clients?
The leaky gut symptoms women describe to me rarely arrive as one neat cluster. This is what I pay attention to:
Reactions to foods that should agree with you, including ordinary whole foods.
Brain fog and low mood.
Skin flare-ups such as eczema, acne or rashes.
Fatigue and joint aches.
Low iron or other nutrient markers when the diet looks solid on paper.
That last one carries a question I ask every time. When a nutrient comes back low, is it intake or absorption? Part one of the series explains how low stomach acid fits in, and this is where the two ideas meet.
On the show I said that eczema and acne are usually gut inflammation. Writing it down, I would put that more carefully. Skin flare-ups can be connected to the gut and the liver, and skin has other causes too, which is why I think of the gut first and a cream second. Some people also feel nothing at all while the immune system is already reacting, so symptoms alone do not settle the question.
Ten symptom questions can show you where to start.
The Gut Repair Blueprint opens with ten symptom-based questions you score yourself. The result points to the section worth reading first, so you spend your energy in the right place.
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What Can Wear Down the Gut Lining?
I look for root causes, and in practice they stack on top of each other. Four come up most with the clients I work with.
Chronic stress. I said this on the show:
We need cortisol. It's the thing that gets you going in the morning. We literally need it to survive. But if it's chronically elevated, it can actually disrupt those tight junctions.
Stress also pulls blood flow away from the gut and towards your muscles, the run-from-the-bear response. Digestion and repair happen in rest and digest. My post on managing stress covers that side.
Food. Ultra-processed foods and refined sugar are the first things I check, with low fibre variety close behind. On seed oils, I asked on the show whether it is the oil or the food it comes packaged in. In client food logs I see butter, olive oil and avocado oil far more than seed oils, and I see a lot of fast food and packaged products. My list of high-fibre foods is a good place to widen the range.
Medication. Antibiotics clear out beneficial bacteria, and NSAIDs (painkillers such as ibuprofen) can damage the lining. Acid blockers called PPIs may increase bacterial overgrowth. Medication stays a decision between you and the doctor who prescribed it, and nobody should stop or change anything on their own. I said it plainly: "I'm not against doctors at all." Medications are necessary.
Low stomach acid. Poor protein breakdown leaves larger food particles and more fermentation, and that can contribute. For the wider picture, my post on improving digestion ties these pieces together.
What Do I Start With First?
Sleep. Before stress work, before food changes, before any supplement:
The very first thing I would have clients work on and lock in and just absolutely nail is their eight hours of sleep every night, allowing the body to heal.
I would take seven or eight hours on a steady schedule, weekends included, with morning sunlight and a tracker if you own one. "I think consistency is going to be the most important thing." I would rather see seven hours every night than five, six, then ten and eleven. My post on sleep deprivation goes deeper.
Then the stress load, which covers more than work. Financial worry, relationships, under-eating and overtraining all count. One client's DUTCH test showed high free cortisol through the day and very low melatonin. The useful question was why melatonin was low, and the cortisol pattern pointed to where to work.
I am the wrong person to preach about slowing down. I tend to push myself too hard if I don't pay attention. Without my Google Calendar I would work a full day and forget to eat. That is why I have a coach, a mentor, daily breathwork, and a walk after lunch and another in the evening. Until sleep and stress are in decent shape, I would hold off on supplements entirely, and I would give the basics at least four weeks before judging anything.
Which Foods and Supplements Do People Look At?
For food I lean towards Mediterranean-style eating, with salmon and other omega-3 sources, built around a plain day-to-day plan you can repeat. The structure matters. If something shows up after dinner, you can swap one food and watch what happens. Bone broth and aloe vera juice are two things I like to layer in, and the plan stays gentle on digestion because the gut has less work to do.
Gluten and dairy are the two foods people struggle with most. On the show I said some people need them out and some do not. In some cases a time-limited experiment makes sense. You pull them for a few weeks with a practitioner, log your symptoms, and then reintroduce one at a time. A strict plan followed by a sudden return to normal tells you very little, which is why a reintroduction plan matters as much as the removal. For several weeks I also ask clients to pull alcohol and ultra-processed foods.
Supplements come last. Glutamine, zinc carnosine, omega-3s and collagen are the ones I named, and I framed them as things people look at, under guidance. I will not give doses here. Which ones fit depends on your history and your medication.
When Do Testing and Extra Help Make Sense?
If symptoms hold steady or get worse after the basics, a GI map that includes zonulin is one test practitioners use, and some read zonulin as a marker linked to permeability. Blood markers such as CRP and TPO antibodies belong with your doctor. Testing works best inside a case you are working through with someone, because gut cases are difficult and the order of steps matters. My advice on the show was to bring a practitioner or doctor in "so that you're not left guessing, buying random supplements and doing things you shouldn't be doing in the wrong order."
The episode runs 36 minutes and covers more than this post could, including how I think about stress and the immune system.
Leaky gut is section two of four.
The free Gut Repair Blueprint covers low stomach acid, leaky gut, gut dysbiosis, and sluggish liver and bile, and the sections still to come in this series are already inside it. Its symptom questions tell you which one to read first.
Download the free Gut Repair Blueprint →
Written by Johan Vesters, functional health and nutrition coach (FNMS, HMCC L1, MMU L1, PN1, CFL1, NCI L1) and founder of Odyssey Coaching Systems.