What dietary recommendations are suggested for individuals with hypothyroidism (underactive thyroid)?

Dietary Recommendations for Hypothyroidism

Individuals with hypothyroidism should ensure adequate iodine intake (150 mcg/day) while following a balanced, nutrient-dense diet that supports overall health, with particular attention to avoiding excessive iodine, ensuring adequate selenium and iron, and timing meals appropriately around levothyroxine administration. 1

Essential Micronutrient Considerations

Iodine Requirements and Monitoring

• Ensure adequate but not excessive iodine intake of at least 150 mcg/day, with an upper limit of 300 mcg/day. 1
• Iodine deficiency impairs thyroid hormone synthesis, while excess iodine (particularly in iodine-deficient populations transitioning to adequate intake) can paradoxically worsen hypothyroidism and increase thyroid autoimmunity. 1
• In populations with high prevalence of thyroid disorders, iodine status should be assessed by 24-hour urinary excretion combined with thyroid function testing. 1
• Avoid excessive iodine from non-dietary sources including iodinated contrast agents, topical iodine disinfectants, amiodarone, and kelp supplements, as chronic excess induces autoimmune thyroiditis and can worsen hypothyroidism. 1

Critical Supporting Nutrients

• Iron and selenium are essential for normal thyroid function at any age. 1
• Iron deficiency specifically impairs thyroid metabolism, as the conversion of T4 to T3 by the liver depends on Type 1 5'-deiodinase, a selenoenzyme. 1
• Selenium supplementation has shown benefit in specific populations, though evidence for generalized supplementation in all hypothyroid patients is limited. 2
• Zinc supplementation may be beneficial in deficient patients, though routine supplementation lacks strong evidence. 2

Vitamin D and Calcium

• Monitor and supplement vitamin D (cholecalciferol) and calcium as needed, particularly in patients with severe hypothyroidism who may have urinary losses of vitamin D-binding protein. 1
• Adequate calcium intake (1200 mg/day) and vitamin D (1000 units/day) are particularly important for patients on thyroid hormone replacement to prevent bone demineralization. 3

General Dietary Pattern Recommendations

Core Dietary Principles

Follow a nutrient-dense dietary pattern emphasizing:

• Vegetables of all types (dark green, red, orange, legumes, starchy vegetables) 1
• Fruits in variety 1
• Whole grains (at least half of grain intake) 1
• Fat-free or low-fat dairy products 1
• Lean proteins including poultry, seafood (at least 2 servings weekly), eggs, and legumes 1
• Healthy oils and unsaturated fats from vegetables, fish, legumes, and nuts 1

Dietary Restrictions and Limitations

• Limit saturated fat to less than 10% of daily calories 1
• Restrict added sugars to less than 10% of daily calories 1
• Reduce sodium intake to less than 2,300 mg per day 1
• Limit trans fats and avoid partially hydrogenated oils 1

Controversial Dietary Restrictions: What to Actually Avoid

Soy Products

• Hypothyroid patients need not avoid soy foods, but should maintain consistent intake patterns. 4
• In euthyroid, iodine-replete individuals, soy foods and isoflavones do not adversely affect thyroid function based on 14 clinical trials. 4
• Critical caveat: Soy may inhibit levothyroxine absorption, potentially increasing the required dose in patients on thyroid hormone replacement. 2, 4
• Patients with marginal iodine intake or compromised thyroid function should ensure adequate iodine consumption if consuming soy regularly. 4

Cruciferous Vegetables

• Avoidance of cruciferous vegetables (broccoli, cauliflower, cabbage, kale) has little proven benefit in patients with hypothyroidism. 2
• These vegetables can be consumed as part of a healthy diet without significant concern for thyroid function. 2

Gluten and Dairy

• Gluten avoidance benefits only patients with concomitant celiac disease or gluten sensitivity, likely by improving levothyroxine absorption. 2
• Dairy avoidance is only beneficial in patients with documented lactose intolerance or dairy sensitivity. 2
• Routine elimination of these foods in hypothyroid patients without documented sensitivities is not evidence-based. 2

Levothyroxine Administration and Dietary Timing

Critical Absorption Considerations

• Take levothyroxine on an empty stomach, typically 30-60 minutes before breakfast, to optimize absorption. 3, 5
• Certain foods and supplements can interfere with levothyroxine absorption, including calcium supplements, iron supplements, soy products, and high-fiber foods when taken simultaneously. 2, 4
• Maintain consistent timing and dietary patterns around levothyroxine administration to ensure stable thyroid hormone levels. 5

Weight Management and Energy Balance

Metabolic Considerations

• Match energy intake to energy expenditure, with appropriate caloric adjustments for weight management when indicated. 1
• Hypothyroidism can reduce metabolic rate, making weight management more challenging; however, adequate thyroid hormone replacement should normalize metabolism. 5
• Regular physical activity is essential for maintaining healthy weight and overall cardiovascular health. 1

Common Pitfalls to Avoid

• Do not pursue extreme dietary restrictions (elimination of entire food groups) without documented medical necessity, as this may lead to nutritional deficiencies. 2
• Avoid excessive supplementation with vitamins and minerals beyond documented deficiencies, as many popular supplements for thyroid health lack evidence of benefit. 6, 2
• Do not rely on dietary modifications alone to manage hypothyroidism; levothyroxine replacement remains the primary treatment. 5
• Avoid iodine megadoses from supplements or kelp, as excess iodine can worsen autoimmune thyroid disease. 1
• Do not assume "thyroid-supporting" supplements (such as ashwagandha, low-dose naltrexone, or various herbal preparations) have proven efficacy, as evidence is lacking or minimal. 2

Special Population Considerations

Pregnancy and Hypothyroidism

• Pregnant women with hypothyroidism require increased levothyroxine doses (typically 25-50% above pre-pregnancy doses) and should not rely on dietary modifications alone. 3, 5
• Adequate iodine intake (150 mcg/day supplementation) is particularly critical during pregnancy for fetal neurodevelopment. 1

Elderly Patients

• Older patients (>70 years) should follow the same general dietary principles but may require more conservative levothyroxine dosing adjustments. 3
• Ensure adequate calcium and vitamin D intake to prevent osteoporosis, particularly in patients on long-term thyroid hormone replacement. 3