Plant-Based Diets: Thyroid Problems And Nutrition

A plant-based diet is one where the majority of what you eat comes from plants. It is associated with a decreased risk of morbidity and mortality from a range of chronic diseases. However, there are concerns that such diets may lack calcium, vitamin D, vitamin B12, and zinc. Iodine is another critical nutrient that may be lacking in plant-based diets as it is mainly found in iodized salt, breads, and dairy. Iodine deficiency can lead to hypothyroidism, skin problems, weight gain, and increased cholesterol levels.

Some plant foods, such as cruciferous vegetables, may also affect iodine consumption due to the presence of thiocyanates. However, there is insufficient evidence to suggest that plant-based diets cause thyroid problems. In fact, studies have shown that a plant-based diet may be protective against hypothyroidism.

The impact of iodine deficiency on thyroid health

Iodine is an essential element for normal growth and brain development. Iodine deficiency occurs when the body does not have enough iodine, usually due to insufficient iodine intake in the diet. This can lead to an enlarged thyroid gland (goiter) and hypothyroidism, as the thyroid works harder to produce thyroid hormones. The thyroid uses iodine to make thyroid hormones, which control heart rate, digestion, and other important functions.

Iodine deficiency is the most common cause of thyroid problems and is especially prevalent in pregnant or breastfeeding individuals, as well as unborn or newborn babies. It can also increase the risk of thyroid autoimmune disease, thyroid cancer, and pregnancy-related high blood pressure. In children, iodine deficiency can lead to learning disabilities and stunt physical and mental growth.

To prevent iodine deficiency, it is recommended to include iodine-rich foods in the diet, such as seafood, iodized salt, and packaged bread. Iodine supplements can also be taken, especially for those planning a pregnancy. However, it is important not to exceed the recommended dosage.

While a vegan diet has been associated with a lower risk of hypothyroidism, vegans can still be at risk of iodine deficiency due to the exclusion of animal products, which tend to be rich in iodine. Soy products, often used as a protein replacement for meat, may also adversely affect thyroid function by interfering with the absorption of thyroid medication. Therefore, it is crucial for vegans to ensure adequate iodine intake through diet or supplements.

In conclusion, iodine deficiency can have a significant impact on thyroid health, leading to hypothyroidism and other related health issues. A well-balanced diet that includes iodine-rich foods or supplements is essential for maintaining optimal thyroid function.

The role of soy in thyroid function

Soy has been a staple in Asian diets for centuries and has been part of Western diets since the 1950s. Soybeans are a healthy and complete source of protein, packed with vitamins, minerals, fibre, and heart-healthy polyunsaturated fat. Soy also contains bioactive compounds known as isoflavones, a phytoestrogen similar to the hormone oestrogen.

Soy and thyroid function

Soy was first classified as a goitrogen in the 1930s—a category of foods and supplements that may alter thyroid hormone production and cause the thyroid gland to enlarge. Laboratory and animal studies found that soy isoflavones affect thyroid hormones in the following ways:

• Prevent the action of thyroid hormones, causing hypothyroidism
• Reduce the absorption of thyroid medications from the intestines
• Stimulate thyroid growth, leading to goitre
• Trigger autoimmune thyroid disease

However, human studies have not shown the same results. A 2019 meta-analysis of 18 clinical trials found that soy has no effect on overall thyroid function. Soy supplementation was linked to a slight rise in thyroid-stimulating hormone (TSH) levels, but this does not appear to have clinical significance. A 2022 review of 417 studies also found that soy isoflavones do not negatively affect thyroid function, thyroid hormone levels, or reproductive hormones.

Soy and iodine

Soy may alter thyroid function in people deficient in iodine. Soy is believed to inhibit thyroid hormone production by interfering with the entry of iodine into the thyroid gland. This can trigger a feedback mechanism that stimulates the pituitary gland to secrete more TSH. However, iodine deficiency is rare in the United States due to universal salt iodization.

Soy and thyroid medication

Soy may prevent the optimal absorption of thyroid replacement medications like levothyroxine. In general, thyroid medication should be taken on an empty stomach to avoid irregular absorption. Soy-containing foods and beverages should be avoided for four hours before and after taking your dose. People taking radioactive iodine (RAI) therapy should also avoid soy products for the duration of the treatment.

Eating soy in moderation does not impact thyroid health, according to current research. Excessive soy consumption, however, may alter thyroid hormone levels and interfere with the production of thyroid hormones. The FDA recommends adults consume 25 grams of soy protein daily. Additional research suggests limiting soy isoflavone consumption to 100 mg or less a day.

The importance of iron for thyroid health

Iron is an essential mineral that plays a crucial role in maintaining thyroid health. It is required for various physiological functions, including the production of thyroid hormones. A deficiency in iron can lead to adverse effects on the thyroid gland and thyroid function.

The Link Between Iron and Thyroid Function

Iron deficiency is a common nutritional disorder worldwide, affecting approximately two billion people, with pregnant women and women of childbearing age being the most vulnerable. This deficiency can impair the synthesis and function of thyroid hormones. Iron is a key component of hemoglobin, which carries oxygen from the lungs to tissues and organs in the body. It is also essential for enzymes and proteins involved in energy production and cell function, including thyroid peroxidase, an enzyme that plays a vital role in thyroid hormone synthesis.

Impact on Thyroid Hormones

Iron deficiency can negatively affect thyroid hormone production and reduce the proliferation of erythrocyte precursors, both directly and by reducing erythropoietin secretion from the kidneys. It can also interfere with the hypothalamic-pituitary-thyroid axis, leading to altered thyroid hormone levels. Additionally, iron is necessary for the activity of thyroid peroxidase, which catalyzes the iodination of tyrosine residues in thyroglobulin, a precursor protein for thyroid hormone synthesis.

Prevalence in Thyroid Conditions

Several studies have reported a high prevalence of iron deficiency in patients with thyroid diseases, particularly hypothyroidism and thyroid autoimmunity. This deficiency can increase the risk of developing thyroid disorders and is associated with impaired thyroid function. The production of thyroid hormones is negatively impacted by iron deficiency, and this can lead to a decrease in thyroid hormone levels and a reduced response to thyroid-stimulating hormone.

Treatment and Prevention

Treating iron deficiency can be done through iron supplementation and/or an iron-rich diet. Iron supplements are typically prescribed, with doses ranging from 60 mg to 120 mg per day, depending on lab results and symptom severity. It is important to note that iron supplements can interfere with the absorption of thyroid medication, so they should be taken separately. An iron-rich diet can also help boost iron intake and includes foods such as red meats, oysters, mollusks, pumpkin seeds, sesame seeds, and iron-fortified foods.

In summary, iron plays a critical role in thyroid health, and its deficiency can have detrimental effects on thyroid function. Treating iron deficiency and maintaining adequate iron levels are important for optimal thyroid health and overall well-being.

The effect of goitrogens on thyroid health

Goitrogens are natural plant chemicals found in some plant foods, such as cruciferous vegetables (broccoli, kale, cabbage, cauliflower, and Brussels sprouts) and soy products. These chemicals are thought to reduce thyroid hormones when consumed in excess.

There is some evidence that goitrogens may lower thyroid hormones, but the research is inconclusive, and the health benefits of these vegetables may outweigh any potential negative effects. For example, broccoli is an excellent source of vitamin C and folate, which may play a role in cancer prevention.

While there is no need to avoid these healthy vegetables, cooking and lightly steaming them can deactivate the goitrogens. This is especially important for those with hypothyroidism or a family history of the condition, as well as those who consume a Western diet high in fast food, processed products, and salt.

Soy-based products, such as tofu, soy protein, tempeh, and edamame, contain isoflavones, which inhibit thyroid peroxidase (TPO), an enzyme involved in thyroid hormone production. However, soy products also have many health benefits, including potential anti-inflammatory effects. Therefore, it is recommended to consult a registered dietitian to determine the appropriate level of soy intake for your individual needs.

In summary, while goitrogens may affect thyroid health, the overall benefits of a plant-based diet rich in fruits, vegetables, and fiber may outweigh the potential risks. A well-rounded, balanced diet is crucial for thyroid health, and unnecessary dietary restrictions should be avoided.

The influence of diet on Hashimoto's thyroiditis

Hashimoto's thyroiditis, also known as chronic lymphocytic thyroiditis, is an autoimmune disorder of the thyroid gland. It is more often diagnosed in women than in men. The disease is characterised by the presence of antibodies in the thyroid gland and infiltration of lymphocytes into thyroid tissue. Treatment includes the replacement of thyroid hormones for hypothyroidism associated with the disease.

The Influence of Diet

Diet can be a complementary treatment for Hashimoto's disease by affecting thyroid function and anti-inflammatory properties. Research shows that diet and lifestyle changes may drastically improve symptoms. There is no specific diet plan proven to treat the disease, but several diets have evidence of having helped people with the condition.

Gluten-Free or Grain-Free Diet

Many people with Hashimoto's experience food sensitivities, especially to gluten. A gluten-free diet may hinder the absorption of vitamin D into the blood and thus hinder therapeutic support in lowering thyroid antibodies.

Sugar-Free Diet

Eating too much sugar can increase inflammation, provoke autoimmune thyroid flares, throw blood sugar out of balance, create gut health issues, and create hormone deficiencies and excesses.

Dairy-Free Diet

Dairy is one of the most problematic foods for people with Hashimoto's, and eliminating it can help reduce bloating, diarrhea, and acid reflux.

Low Glycemic Index Diet

A low glycemic index diet can help keep blood sugar levels in balance. Blood sugar imbalances are common in people with Hashimoto's, and some research indicates that people with this condition are more prone to spikes in blood sugar followed by reactive hypoglycemia after eating a carbohydrate-rich meal.

Foods to Eat

• Fruits
• Non-starchy vegetables
• Healthy fats
• Animal protein
• Gluten-free grains
• Seeds, nuts, and nut butters
• Beans and lentils
• Dairy and non-dairy substitutes (fortified with calcium and/or vitamin D)
• Spices, herbs, and condiments
• Beverages

Foods to Avoid

• Added sugars and sweets
• Fast food and fried foods
• Refined grains
• Highly processed foods and meats
• Gluten-containing grains and foods
• High-glycemic fruits
• Nightshades
• Soy
• Lectins

Frequently asked questions