Your Gut Is Running Your Thyroid And Possibly Making Your Hashimoto's Worse

By Anca Vereen, Integrative Dietitian, Somatic Psychotherapist

When people first hear me talk about gut health in the context of Hashimoto's, I often get a quizzical look. "I came here about my thyroid," they say. And I understand that reaction completely. We have been conditioned to think of these things in isolation. But the more I work with Hashimoto's patients, the more convinced I am that the gut is where so much of the action is happening.

Let me explain why.

Hashimoto's Starts in the Gut (At Least Partly)

For an autoimmune disease to develop, three things must be present: a genetic predisposition, a trigger, and intestinal permeability, what is commonly called leaky gut. Remove any one of those three legs, and the autoimmune process cannot take hold.

Leaky gut occurs when the tight junctions that line the intestinal wall become compromised. Instead of selectively allowing nutrients through while keeping bacteria, undigested food particles, and toxins out, the barrier breaks down and allows things through that should not be there. These particles enter the bloodstream, activate the immune system, and in genetically predisposed individuals, can trigger the autoimmune cascade that becomes Hashimoto's.

Research published in 2024 confirmed that Hashimoto's patients show significantly increased serum zonulin levels, which is a key marker of intestinal permeability, positively correlated with TPO antibody levels. In plain language: the leakier the gut, the higher the antibodies. This is not a coincidence. It is a mechanism.

The Microbiome Difference in Hashimoto's

Research has consistently found that the gut microbiome of Hashimoto's patients looks distinctly different from that of healthy individuals. There is lower diversity of bacterial species and meaningful differences in the specific strains present.

What does this mean in practice? The gut microbiome performs critical functions for thyroid health. It activates thyroid hormones, assists in T4 to T3 conversion, modulates the reabsorption of thyroid hormones, and regulates iodine metabolism. A disrupted microbiome impairs all of these processes.

Research published in Frontiers in Nutrition in 2024 identified specific bacterial strains including Akkermansia, Ruminococcaceae, and Butyrivibrio that have protective effects against hypothyroidism. Akkermansia in particular, which plays a crucial role in maintaining the integrity of the gut lining and regulating immune function, is commonly depleted in autoimmune conditions.

When the microbiome is disrupted, the downstream effects compound. Reduced short-chain fatty acid production impairs the gut barrier further. Elevated bacterial endotoxins (LPS) increase systemic inflammation. The immune system becomes hyperactivated. And the thyroid takes the hit.

The Gut and Hashimoto's Web

Hypothyroidism itself impairs gut function in ways that make the whole situation worse. Reduced intestinal motility, meaning the gut moves too slowly, creates conditions for bacterial overgrowth (SIBO). Reduced gallbladder contraction impairs fat digestion and fat-soluble vitamin absorption. Digestive enzyme production decreases, leading to malabsorption. Intestinal secretory IgA, which is the gut's first line of immune defence, becomes suppressed.

You end up in a situation where Hashimoto's impairs gut function, and impaired gut function worsens Hashimoto's. Each feeds the other. Without intervening on both sides simultaneously, it is very hard to make meaningful progress.

The liver is part of this picture too. The thyroid and liver have an intimate reciprocal relationship: thyroid hormones regulate liver metabolism, and the liver activates and clears thyroid hormones. In Hashimoto's, reduced thyroid hormone activity leads to liver hypometabolism, impaired bile acid production, reduced gallbladder contraction, impaired clearance of cholesterol, and reduced phase I and phase II detoxification. Toxins, excess hormones, and metabolic byproducts accumulate. This adds another layer of inflammatory burden to an already strained system.

What I Focus on for Gut Health in Hashimoto's

The most important dietary change I see making a consistent difference is gluten elimination. Gluten is a driver of intestinal permeability in susceptible individuals, and there is a well-established cross-reactivity between gluten proteins and thyroid tissue. Beyond gluten, dairy proteins (particularly casein and casomorphin) are the next most common reactants. A 2024 study using comprehensive food immune reactivity testing also flagged coffee, chocolate, and certain grains as common triggers in Hashimoto's, though individual responses vary.

Healing the gut lining requires adequate protein, which provides the building blocks for tissue repair. Zinc, vitamin A, and bone broth or collagen peptides all support intestinal barrier integrity. Probiotic supplementation, particularly with strains that have been specifically researched for Hashimoto's, shows promising effects on antibody levels and thyroid function. A 2025 double-blind trial on Lactiplantibacillus plantarum 299v showed improved outcomes in women with Hashimoto's.

Supporting the liver alongside the gut is essential. This means cruciferous vegetables for glucosinolate support of detoxification pathways, adequate fibre for hormone clearance, and ensuring sufficient B vitamins for methylation.

And selenium deserves special mention. A 2024 meta-analysis confirmed that selenium supplementation significantly reduces both TPO and thyroglobulin antibodies. Selenium is both a key component of the enzymes that activate thyroid hormones and a major antioxidant protector for the thyroid gland. Brazil nuts, sardines, and eggs are good food sources, or supplementation at around 200mcg per day under practitioner guidance.

The gut is not a side issue in Hashimoto's. For many of my clients, it is the most important issue. And when we address it properly, the results are often remarkable.

Anca Vereen is an integrative dietitian specialising in autoimmune and hormonal health. Visit ancavereen.com to work together.