IBS and Thyroid: How Hypothyroidism and Hashimotos Affect Your Gut

May 24, 2026

IBS and Thyroid: How Hypothyroidism and Hashimoto's Affect Your Gut

By Dr. Onikepe Adegbola, MD PhD — Johns Hopkins-trained physician-scientist and founder of Casa de Sante

Key Takeaways

Thyroid disease and IBS overlap significantly — hypothyroidism causes constipation, bloating, and motility changes that mimic IBS-C
Up to 50% of patients with hypothyroidism report IBS-like symptoms. Many IBS patients have undiagnosed thyroid dysfunction.
Hashimoto's thyroiditis (autoimmune hypothyroidism) has a gut connection: increased intestinal permeability, molecular mimicry, and microbiome disruption
Thyroid hormone directly regulates gut motility — T3 receptors are present on intestinal smooth muscle cells
Optimizing thyroid function often improves IBS symptoms, and improving gut health may reduce Hashimoto's antibody levels

The Thyroid-Gut Connection

Thyroid Hormone and Motility

Hypothyroidism (low thyroid): Slow motility → constipation, bloating, abdominal distension. Reduced gastric acid → impaired digestion, SIBO risk. Slowed biliary function → fat malabsorption. These symptoms are often diagnosed as IBS-C when the thyroid hasn't been checked.
Hyperthyroidism (high thyroid): Accelerated motility → diarrhea, urgent bowel movements, malabsorption. Can mimic IBS-D.
Subclinical hypothyroidism: TSH is mildly elevated but T3/T4 are "normal." GI symptoms may still be present because tissue-level thyroid hormone action is impaired before blood levels change.

Hashimoto's and the Gut

Hashimoto's thyroiditis is an autoimmune condition where the immune system attacks the thyroid. The gut connection:

Intestinal permeability: Hashimoto's patients have significantly increased intestinal permeability compared to healthy controls. "Leaky gut" allows food proteins and bacterial fragments to cross into the bloodstream, triggering immune responses.
Molecular mimicry: Gliadin (a wheat protein) structurally resembles thyroid tissue. In genetically susceptible individuals, the immune response against gliadin may cross-react with thyroid tissue — driving Hashimoto's.
SIBO: Hypothyroidism-induced slow motility creates a breeding ground for small intestinal bacterial overgrowth. SIBO worsens gut symptoms AND may perpetuate the autoimmune process.
Microbiome: Hashimoto's patients have reduced microbial diversity, lower Lactobacillus and Bifidobacterium, and increased Prevotella.

What to Do

Get Tested

If you have IBS (especially IBS-C) and have NOT had thyroid testing, request:

TSH: Screening test. Optimal range 0.5-2.5 mIU/L (not just "normal range" of 0.5-4.5)
Free T4: Active thyroid hormone
Free T3: The most metabolically active form
TPO antibodies: Screen for Hashimoto's autoimmunity
Thyroglobulin antibodies: Additional Hashimoto's marker

Gut Strategies for Thyroid Patients

Treat SIBO if present: Breath testing → treatment → motility improvement
Consider gluten removal: The molecular mimicry between gliadin and thyroid tissue is well-documented. Many Hashimoto's patients see antibody reduction on a gluten-free diet. This is not proven for all patients but is worth a 3-month trial.
Support the microbiome: Probiotics with Lactobacillus and Bifidobacterium specifically. These strains are depleted in Hashimoto's.
Address intestinal permeability: Collagen, glutamine, zinc, vitamin D — the standard gut barrier repair protocol.
Selenium: 200 mcg/day. Selenium is essential for thyroid hormone conversion (T4→T3) and has been shown to reduce TPO antibodies in Hashimoto's patients.
Optimize vitamin D: Vitamin D deficiency is strongly correlated with Hashimoto's severity. Target 40-60 ng/mL.

🛒 Thyroid-Gut Support

Daily Vitamin — Selenium, zinc, vitamin D, and iodine are all critical for thyroid function. Many thyroid patients are deficient in multiple nutrients. A comprehensive daily vitamin addresses the foundation.
FODMAP Enzymes + Probiotics — Restores the Lactobacillus and Bifidobacterium populations depleted in Hashimoto's. Supports the microbiome-immune axis that drives autoimmune thyroid disease.
Collagen Peptides — Repairs the intestinal permeability documented in Hashimoto's. Sealing the gut barrier may reduce the antigen exposure driving autoimmune activation.
Regularity Companion — Hypothyroid constipation is notoriously resistant to standard treatments. Motility support addresses the slow transit directly.

Medical Disclaimer: This article is for educational purposes only. Thyroid conditions require proper diagnosis and treatment by an endocrinologist. Do not self-treat thyroid disease. Thyroid medication (levothyroxine) should be taken on an empty stomach, 30-60 minutes before food and other supplements. Dr. Adegbola is the founder of Casa de Sante.

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