What foods should a patient with hypothyroidism (underactive thyroid) avoid or limit?

Foods to Avoid or Limit in Hypothyroidism

Patients with hypothyroidism should primarily avoid excessive iodine intake, soy products that interfere with levothyroxine absorption, and certain supplements that impair thyroid hormone medication effectiveness. 1

Iodine-Related Restrictions

While iodine is essential for thyroid hormone production, excessive intake can paradoxically worsen hypothyroidism in iodine-sufficient individuals:

• Limit iodine to approximately 150 μg/day for adults, with an upper limit of 300 μg/day to prevent worsening of thyroid function 1
• Avoid iodine-containing medications and supplements, as these can interfere with thyroid function 1
• Use iodized salt in moderation rather than avoiding it completely, as adequate (not excessive) iodine is still necessary 1
• Be cautious with seaweed and kelp products, which contain extremely high iodine concentrations 2
• Consume seafood, especially shellfish, in moderation due to naturally high iodine levels 2

Soy Products and Levothyroxine Interference

Soy products significantly interfere with levothyroxine absorption and should be avoided or consumed several hours away from thyroid medication:

• Soy formula, soy milk, and soy-based foods can prevent adequate absorption of levothyroxine, leading to persistent hypothyroidism despite appropriate medication dosing 3, 4
• Clinical cases demonstrate that infants and children with congenital hypothyroidism consuming soy products required dramatically increased levothyroxine doses and remained clinically hypothyroid until soy was discontinued 4
• If soy foods cannot be avoided entirely, they should be consumed at least 4 hours away from levothyroxine administration 3
• Hypothyroid patients do not need to completely eliminate soy if their iodine intake is adequate, but timing separation from medication is critical 3

Protein Supplements and Additives

Over-the-counter protein supplements, particularly whey protein, can impair levothyroxine absorption:

• Whey protein supplements delay gastric emptying and reduce ileal nutrient absorption, interfering with thyroid hormone medication 5
• Additives in protein supplements such as papain enzyme and soy lecithin may further impair levothyroxine absorption 5
• Patients on stable levothyroxine doses who introduce protein supplements may experience TSH elevation and return of hypothyroid symptoms 5
• If protein supplementation is necessary, take it at least 4 hours away from levothyroxine 5

General Dietary Considerations

Focus on cardiovascular-protective foods, as hypothyroid patients have increased cardiovascular risk:

• Limit processed foods high in sodium, which compound cardiovascular risk in hypothyroidism 1
• Emphasize whole foods including fruits, vegetables, whole grains, lean proteins, and healthy fats 1
• Include iodine-rich foods in moderation such as fish, dairy products, and iodized salt 1
• Be aware that organic milk and plant-based milk alternatives contain less iodine than conventional dairy 1

Critical Medication Timing

The most important dietary consideration is timing food intake away from levothyroxine administration:

• Take levothyroxine on an empty stomach, at least 30-60 minutes before breakfast or other medications 6
• Avoid calcium supplements, iron supplements, and multivitamins containing minerals within 4 hours of levothyroxine 6
• Coffee and high-fiber foods may also impair absorption and should be separated from medication timing 6

Common Pitfalls to Avoid

• Do not assume all "healthy" supplements are safe - many interfere with thyroid medication absorption 5
• Do not consume soy products near medication time - even if soy is part of your regular diet, timing is critical 4
• Do not take excessive iodine supplements thinking more is better - this can worsen hypothyroidism 1
• Do not ignore TSH changes after introducing new dietary supplements or protein powders 5