Which Foods Inhibit and Promote Thyroid Function?

Thyroid Physiology and Metabolic Regulation

The thyroid gland, a small butterfly-shaped glad that hugs the trachea, exerts substantial influence over metabolic processes throughout the body. It's controlled by the pituitary gland, which releases TSH when thyroid levels get low. The thyroid is responsible for taking in iodine and converting it to thyroid hormone T4, which is converted to T3 that is stronger. Yet, synthetic T4 is the most commonly prescribed thyroid hormone, and provides almost no effect for many people, or even worsens their symptoms. This continues despite the established medical research showing that the diagnostic measures for determining low thyroid are inadequate, effectivly ignoring those who have have Hashimoto's or trouble with converting T4 to T3. Naturopaths, and other alternative medical providers should run a full thyroid panel that tests for all the hormones, including Reverse T3, and other antibodies that can indicate Hashimoto's. 

The thyroid's secretions are involved in cerebral functions, gastrointestinal tract operations, cardiovascular health, lipid and cholesterol metabolism, hormone synthesis, and both gallbladder and hepatic activities. Alarmingly, approximately 20 million Americans contend with thyroid disorders, with 60 percent remaining undiagnosed. One in every eight women is likely to develop a thyroid condition during her lifetime. Disruptions in thyroid functionality can precipitate extensive health ramifications.

According to Dr. Spurlock MD: 

"Every cell in your body depends upon thyroid hormones for the regulation of its metabolism. A healthy thyroid gland generally produces about 80% T4 and about 20% T3, however, T3 possesses about four times the hormone “strength” as T4. T3 and T4 control your body’s metabolism. If you don’t have enough hormones, then your metabolism slows down. Your metabolic rate dictates how quickly you process food, how fast your heart beats, how much heat your body generates, and even how quickly you can think. In short, T3 and T4 are in charge of how your body uses energy. Despite T3 being the stronger of the two, taking synthetic T4 hormone is considered the “standard” treatment for hypothyroidism, with the reasoning being that the body will take T4 and turn it into T3. However, this is not always the case and it can often occur that when T4 is taken very little T3 is produced. This is why some people have little to no effect from taking common thyroid treatments as they are a synthetic T4 and their body is not effectively transforming it into T3. "

What Are Goitergenic Foods?

The term "goitrogenic" pertains to entities that induce "goiter," characterized by enlargement of the thyroid gland. Goitrogens impede iodine uptake by the thyroid, hampering its ability to synthesize adequate levels of thyroid hormones T4 and T3. In response to deficient T4 levels, the hypothalamus releases thyroid-stimulating hormone (TSH)-releasing hormone, inciting the pituitary gland to produce TSH. The thyroid, in turn, attempts to augment hormone production. Should this compensatory mechanism falter, glandular hypertrophy ensues.

Goitrins, thiocyanates, and nitriles, derived from glucosinolates—natural plant-derived pesticides—are prominent goitrogenic chemicals. During digestion, enzymatic breakdown of glucosinolates yields both goitrogenic and non-goitrogenic byproducts. Identified goitrogenic foods encompass cruciferous vegetables such as bok choy, broccoli, Brussels sprouts, cabbage, canola, cauliflower, and Chinese cabbage, among others. Additionally, the Rosaceae family—almonds, apricots, cherries, peaches, pears, plums, raspberries, and strawberries—exhibits goitrogenicity. Other notable examples include bamboo shoots, millet, soy, spinach, sweet potato, tapioca, and yuca (cassava or manioc).

Environmental Agents

Environmental chemicals and certain pharmacological agents also possess goitrogenic properties, including amiodarone, antibiotics, bromides, dioxins, heavy metals, NSAIDs, lithium, benzodiazepines, oxazolidines, perchlorates, pesticides, and thiocyanates.As noted by Ryabuka 2022,

"The main causes of thyroid disorders include iodine deficiency in the environment, exposure to a number of widely used chemicals (thyrodisruptors), heavy metal ions. A variety of physical environmental factors are important. A significant increase in thyroid cancer is frequently associated with local or general exposure to ionizing radiation. Prolonged exposure to electromagnetic fields can lead to disorders in the gland's homeostasis. The functional capacity of the gland is also impaired by unsanitary living conditions, some bacteria and viruses, and improper nutrition."

At even low concentrations, environmental toxins and goitergens curtail iodine assimilation by the thyroid, a condition often ameliorated by iodine supplementation. However, elevated goitrogen exposure obstructs iodine incorporation into thyroid hormones, precluding effective usage by the gland and rendering iodine supplementation ineffectual.

Preparation of Goitrogenic Foods

Despite potential health risks, goitrogens do not unequivocally negate the benefits of consuming kale and broccoli. Fruit and vegetable intake is associated with reduced chronic disease risk. Crucially, the goitrogen content of foods varies significantly and can be modulated through cooking. Cruciferous vegetables, particularly kale, collard greens, and Brussels sprouts, are the primary goitrogenic sources. Progoitrin levels per dry weight in Russian kale exceed those in Chinese cabbage by approximately 150 times. 

Top Foods To Avoid:

Gluten and other Grains

A range of autoimmune diseases can be traced to gluten sensitivity. For example, Addison's disease, Sjogren's syndrome, and autoimmune thyroid disease have been linked to gluten allergies. Women with autoimmune hypothyroidism have been helped by eliminating grains like wheat, rye, oats, and barley. 

Cruciferous Vegetables

According to Dr. Izabella Wentz, the glucosinolates in vegetables like broccoli, cabbage, and kale may act as goitrogens and impair the uptake of iodine into the thyroid. However, according to Dr Wentz, they are generally alright for those with Hashimotos disease, since they would have to be consumed in high amounts, uncooked, to become a problem. However, to be on the safe side, it might be advisable to eat them sparingly. 

Strawberries

Although many health website say that strawberries are a low concern, they are one of the highest goitergenic foods. Dr. Minkoff, MD, of LifeWorks Wellness Center, writes that strawberries can lead to enlarged thyroid or worsen other thyroid conditions. 

Soy

Isoflavones from soy are another problematic food for the thyroid, namely due to their ability to compete with thyroid hormones for iodine. Sufficient iodine levels are able to prevent this, but many people have sub-clinical deficiencies in iodine. Cooking soy, and combining it with iodine-rich foods can mitigate the negative impacts on thyroid function. It's best to avoid hydrolyzed soy protein. 

Heating and Processing Foods

Thermal processing, particularly steaming, diminishes goitrogenic content by two-thirds, while boiling for 30 minutes eliminates 90 percent of goitrogens through myrosinase activation, an enzyme deactivating goitrogenic glucosinolates. Nevertheless, boiling leads to some nutrient loss—45 percent of vitamin C, 20 percent of thiamin, and 40 percent of folate. Minerals, vitamin B12, and vitamin A remain relatively intact. Steaming retains more nutrients than boiling, generally rendering cooked goitrogenic foods beneficial. Conversely, fermentation increases cabbage's goitrogen levels but reduces nitriles, which are more detrimental, thus yielding a net positive effect. Moderate consumption of goitrogenic foods poses minimal risk. However, frequent intake of raw kale or spinach, especially in smoothies, warrants caution regarding thyroid function.

Patient Populations Vulnerable to Goitrogenic Effects

Certain patient groups warrant careful monitoring of goitrogenic food intake:

• Iodine-Deficient Individuals: Goitrogens exacerbate iodine deficiency, prevalent in up to 44 percent of Europe's population. Optimal iodine sources include seaweeds, cod, shrimp, and tuna, augmented by eggs and iodized salt. Simultaneous selenium intake from Brazil nuts, mushrooms, seafood, poultry, and other sources is advised.

• Patients with Thyroid Disorders: In hypothyroidism, goitrogens exacerbate symptoms. Limiting cooked cruciferous vegetables to one serving per day is recommended.

• Pregnant and Nursing Women: These individuals require 50 percent more iodine, rendering them susceptible to deficiency. Approximately 47 percent of Boston mothers' breast milk lacks adequate iodine. Limiting intake to three to five weekly servings of cooked cruciferous vegetables is advised.

Additional Dietary Considerations for Thyroid Health

• Oxalates: Found in plants, oxalates bind minerals, reducing bioavailability and increasing kidney stone risk, especially with dysbiosis. Cooking minimally reduces oxalate content.

• Immune Response Triggers: Eggs, nightshades, and dairy may exacerbate autoimmune thyroid disorder.

• Industrial Seed Oils: High omega-6 fatty acids in these oils contribute to inflammation.

• Very-Low-Carb or Low-Protein Diets: Insufficient carbohydrates and proteins impede T4 to T3 conversion. A minimum of 20 percent carbs and 10 percent protein is recommended.

Signs of Thyroid Disease

• Constipation
• Fatigue
• Irritability
• Memory lapses
• Sleep problems
• Thinning hair
• Weight gain  

To address thyroid disorders, further strategies include stress management—stress impairs thyroid function—gut health optimization, vitamin D monitoring, bromide avoidance, and toxin exposure minimization. For expanded insights, refer to my articles on thyroid-related cardiovascular, microbiome, and glucose interactions. Encouraging moderation in goitrogenic food consumption, particularly through steaming or boiling, is advisable for patients with thyroid conditions.

Top Foods to Consume

• Iodine-rich foods like seaweed, fish, oysters, clams, shrimp, eggs, and garlic. Lugol's Iodine is one of the most potent Iodine supplements available. 
• Zinc-rich foods like Oysters, meat, sunflower seeds and pumpkin seeds. 
• Iron-containing foods: Foods like beets, pumpkin, beans, carrots, and nutritional yeast can be high sources of iron. 
• Selenium-high foods: The highest source of selenium is Brazil nuts, with enough in one single nut for your daily requirement. Fish and other meats also contains some amounts. 
• B-Vitamins: Found in nutritional yeast, eggs, milk and dairy, and avocados, are high sources of B-vitamins. 
• Aloe Vera: According to Dr. Wentz, Aloe Vera taken orally can increase antibodies and thyroid function, among many other benefits. It is high in B12 unlike most other plants, and contains trace minerals like chromium, zinc, selenium, as well as the amino acid tyrosine, which is the main precursor amino acid for thyroid hormone. It has been found to be as effective as selenium for Hashimoto's. In studies, a mere 50ml of Aloe Vera juice per day was found to significantly decrease in TPO antibodies after 6 months. Another study found that aloe enhanced certain immune responses, inhibits proinflammatory cytokines, and stimulates white blood cells due to its high poly saccharides.  

Sources

Metro D, Cernaro V, Papa M, Benvenga S. Marked improvement of thyroid function and autoimmunity by Aloe barbadensis miller juice in patients with subclinical hypothyroidism. J Clin Transl Endocrinol. 2018;11:18-25. doi:10.1016/j.jcte.2018.01.00