Leaky Gut

What is leaky gut?

Leaky gut — clinically known as intestinal permeability — describes a state in which the tight junctions between cells lining the small intestine loosen, letting particles cross into the bloodstream that should have stayed in the gut.

The gut lining is meant to be selectively permeable: nutrients pass through, while bacteria, toxins, and undigested food particles are kept out. When this barrier is compromised, those particles leak through and the immune system — which lives largely in the gut wall — reacts. Over time, this systemic immune activation drives inflammation, food sensitivities, and autoimmune disease.

Intestinal permeability used to be considered fringe. It is now a well-described phenomenon in mainstream gastroenterology, with measurable markers like zonulin (a regulator of tight junctions) and lactulose-mannitol urine testing.

Why leaky gut matters

Leaky gut is one of the most consequential upstream drivers in Functional Medicine because it links seemingly unrelated symptoms to a single mechanism.

Common contributors include:

• Gluten — the strongest known trigger of zonulin release, in everyone, not just celiacs (see Gluten And Thyroid)
• Chronic stress and HPA axis activation — see Hpa Axis
• Gut infections and dysbiosis — overgrowth of unfavorable bacteria, yeast, or parasites
• NSAIDs, frequent antibiotics, and certain medications
• Alcohol and ultra-processed food intake
• Low stomach acid and impaired digestion
• Nutrient deficiencies — especially zinc, vitamin A, and L-glutamine

When the barrier is leaky, downstream effects include:

• Autoimmune disease — including Hashimotos Thyroiditis and other thyroid autoimmunity
• Food sensitivities that seem to multiply over time
• Skin conditions — eczema, rosacea, acne
• Joint pain and unexplained inflammation
• Brain fog, anxiety, and mood symptoms (the gut-brain axis)
• Nutrient malabsorption — especially iron, B12, magnesium, and zinc

How MTC applies leaky gut

For any woman with autoimmune thyroid disease, leaky gut is assumed to be playing a role until proven otherwise. The research is too consistent to ignore: you cannot have autoimmunity without intestinal permeability somewhere in the picture. Repairing the gut lining is foundational to calming the autoimmune fire.

At Modern Thyroid Clinic, the gut work usually layers in this order:

• Remove triggers — typically gluten first, often dairy and processed foods, sometimes individualized food sensitivities
• Repair the lining — L-glutamine, zinc carnosine, vitamin A, collagen, deglycyrrhizinated licorice, slippery elm
• Reinoculate — targeted probiotics and fermented foods to rebuild a healthy microbial community
• Address infections — SIBO, yeast overgrowth, H. pylori, parasites, when present, with appropriate testing and treatment
• Restore digestion — adequate stomach acid, digestive enzymes, bile flow
• Calm the nervous system — chronic stress keeps the gut leaky no matter what supplements you take

This work pairs naturally with the broader Gut Thyroid Connection. Many women find that as the gut heals, thyroid antibodies fall, food sensitivities ease, and the systemic inflammation that fueled fatigue, joint pain, and brain fog quietly resolves. The thyroid medication may stay the same — but the experience of being in your body changes.