The current state of knowledge related to diet in Hashimoto Thyroiditis (HT) is far from satisfactory, as many HT subjects experience several disorders and report reduced quality of life.
Chronic lymphocytic thyroiditis (Hashimoto thyroiditis, Hashimoto, HT) is the most frequent autoimmune disorder and the cause of hypothyroidism in iodine-sufficient countries. Diagnosed hypothyroidism affects 1%–3% of the population, while subclinical hypothyroidism is more common (estimated at 4%–10%). Abnormal functioning of the thyroid gland is diagnosed in 22% of the population. Women had thyroid gland disease almost nine times more often than men and diagnosis since 2004 has increased possibly due to more accurate measures and barrowing the range.
Thyroid hormones control growth, metabolism, and body development and take part in the production of structural proteins, enzymes, and other hormones. The majority of subjects with thyroid disease experience problems in maintaining normal body weight and have a higher body mass index and waist circumference than healthy subjects. Some studies show that the total metabolic rate can be lowered by up to 50% in serious cases of hypothyroidism which supports body weight gain and predisposes patients to obesity, even when a patient’s physical activity and dietary energy load are the same as before diagnosis. The process of converting energy foods, carbohydrates, protein and fat, to energy worsens, including glucose metabolism. Studies have shown in some populations where HT is high such as Poland, that it co-occurred with diagnosed diabetes in 27% of HT subjects and fasting blood glucose level or impaired glucose tolerance in about 17% of HT subjects. Furthermore, even after normalizing thyroid function via hormonal replacement, many HT individuals persist with numerous symptoms, such as chronic fatigue and irritability, dry skin, hair loss, nervousness, and impaired quality of life.
Medical management with thyroid hormone replacement is the fundamental treatment in HT. Nutrition can support the treatment and the impact of diet on thyroid function cannot be denied, as dietary micronutrients play a role in thyroid hormones synthesis. To date, there is limited information from well-evidenced studies, and none of the scientific societies have developed comprehensive dietary recommendations on HT. (1)
A summary of diet and HT (1)
The consumption of vegetables is recommended several times a day, which is in line with the recommendation for the general population. Various kinds of vegetables are recommended, although attention should be paid to the consumption of soybean-related foods and raw cruciferous vegetables. The special function of vegetables for HT subjects can be attributed to phytosteroles. These compounds are present in vegetables in moderate amounts and have shown immunomodulatory and anti-inflammatory properties. Both functions can have a positive and a negative effect on health.
Foods Rich in Calcium
Foods rich in calcium (e.g., milk, fermented milk drinks, curd cheese, cheese), the recommended consumption frequency is several times a day, which is in line with the recommendation for the general population. Calcium deficiencies can have serious consequences for the health of women with hypothyroidism. The main role of thyroid hormones is metabolism regulation, but it also participates in bone tissue reconstruction. One consequence of hypothyroidism is a reduction in the processes of bone tissue reconstruction resulting from the inhibition of bone mineralization. Therefore, the diet of patients with hypothyroidism should be rich in dietary calcium, such as milk, yoghurt, cheese, low-, regular-, or high-fat dairy, and small fish eaten along with bones. Some studies on HT have focused on lactose intolerance diagnosed with an elimination diet, hydrogen tests, lactose tolerance tests, or small intestinal biopsies. It was found that 75% out of 84 patients with HT, all of whom were residents of the Mediterranean Sea region and Turkey, had lactose intolerance. Other studies have found that lactose elimination from the diet of HT patients decreased the TSH level without a modification dose of levothyroxine suggesting that lactose testing might be a good precaution.
Fruit consumption is recommended at least once a day, similar to the recommendation for the general population. Fruits and vegetables are an abundant dietary source of polyphenols and micronutrients in the human diet and well known for their anti-inflammatory, immunomodulatory, and antioxidant effects in the body. Studies have reported an association of a vegan diet (rich in fruits and vegetables) and a lower risk of hypothyroidism.
The recommended consumption of whole grains, e.g., buckwheat, wholemeal wheat, and rye bread, at least once a day, is in line with the recommendation for the general population. A gluten-free diet has been given a lot of attention with respect to HT and the literature shows that celiac disease (CD) is associated with an increased prevalence of autoimmune thyroid disease (AITD) and vice versa, with a prevalence of up to 9% of adults with AITD. It is because CD has shown a prevalence of hypothyroidism in 2% to 5%, that the suggestion of going gluten-free diet may bring clinical benefits to subjects with autoimmune thyroid disease. Authors of a number of studies have debated these findings, arguing that there is little evidence to support the findings. It still remains a controversial as to its effectiveness with thyroid issues but mandatory for celiac disease. Currently, the recommendation for whole grains results from the content minerals, vitamins, and dietary fiber supplied by these foods and especially selenium.
Animal Foods Rich in Zinc
The consumption of animal foods rich in zinc (e.g., meats and eggs) several times a week is recommended. There are reports that zinc deficiency is one of the causes of subclinical hypothyroidism and that zinc deficiency leads to a reduction in the level of FT4 and FT3 and the development of hypothyroidism symptoms. In humans, zinc supplementation brought the thyroid function back to normality in hypothyroidean patients. A zinc supplement is often been used for a time to bring levels up and ensure adequate dietary zinc rich foods are consumed.
Animal Foods Rich in Selenium
The findings that diets rich in selenium may increase the production of active thyroid hormone and reduce TgAb and TPOAb are well established. Studies often reveal that selenium intake and selenium status is suboptimal in European and Middle Eastern countries, with lower levels in the Middle East. The most recent meta-analysis found that the use of selenium supplements reduced serum TPOAb levels after 3, 6, and 12 months in HT patients treated with levothyroxine and after three months in untreated cases.
Plant sources of selenium, i.e., nuts and seeds, are also rich in zinc.
Fish and seafood are rich in selenium and omega 3 fatty acids and muscle and organ meats are rich in selenium.
Nuts and Seeds
Various kinds of nuts and seeds are recommended to be consumed several times a week. These foods are a good source of selenium and zinc (both important in thyroid metabolism) and also rich in dietary fiber. Brazil nuts are the richest food source of selenium, 2 nuts contributing 200mcg. In general, all nuts are a good source of zinc as well as some seeds such as black cumin. Pumpkin, sunflower and sesame seeds are also well studied for their nutrient benefits.
Foods with Limited Consumption
Raw Cruciferous Vegetables
The consumption of raw cruciferous vegetables, e.g., kale, bok choy, white cabbage, red cabbage, broccoli, brussels sprouts, and cauliflower should be limited (once a week or less). Cruciferous vegetables, as well as soybean-related foods, contain goitrogens, which interfere with thyroid hormone production and utilization. A goiter may be a response to an overactive or underactive thyroid gland. Unless there is a co-existing iodine deficiency, these foods are generally of no clinical significance according to the statement of the Institute of Medicine. Goitrogens are inactivated by heating and cooking—the thermal processing leads to inactivation of about 30% of goitrogens. Thus, it is important to educate patients on how to prepare these vegetables.
Sweets, Sugar, and Honey
Limiting the consumption of sweets, sugar, and honey including high-sweetened jam and fruits candied (once a week or less) is recommended, as these foods are a source of monosaccharides and many of these foods contain a large amount of saturated fatty acids and trans-isomers of unsaturated fatty acids. This recommendation is in line with the recommendations for the general population to prevent obesity, diabetes, and other diseases, including cancers. It should be underlined that the risk of the development of diabetes is greater in HT patients than people without thyroid diseases. Although the autoimmune character of the HT predisposes to type 1 diabetes, pro-inflammatory cytokines also have an influence on receptor insulins, which can lead to impairment of their function and the development of insulin resistance and type 2 diabetes.
Sweetened Beverages and Energy Drinks
Limiting the consumption of sweetened beverages energy drinks (once a week or less) regardless of the sweeteners type (sugar, glucose–fructose syrup or artificial sweeteners, etc.) is recommended. Sweetened beverages can affect hormonal levels in the blood by increasing T4 and parathyroid hormones, and lowering T3 and aldosterone levels. Animal studies report that artificial sweeteners affect the immune system and show that sucralose diminishes the thyroid axis activity. Energy drinks, regardless of whether they are standard or low-calorie drinks, commonly contain sugar substitutes such as saccharin, aspartame, sucralose, acesulphame K, and neotame. Clinical reports show that the intake of artificial sweeteners may play a role in AITD and lead to increased TSH.
Limiting the consumption of fast food (once a week or less) is recommended. The recommendation for the general population is to avoid fast food. There is a growing, alarming trend of fast food consumption associated with a worsening of cardiometabolic outcomes, including obesity. It was reported that the consumption of fast foods ≥2 times/week increased the risk of insulin resistance. In adults, every one-meal/week increase in fast food and sit-down restaurant consumption was associated with an increase in BMI.
Soybean and Millet
Soybean and millet—e.g., soya: seeds, sprouts, tofu, milk; millet groats—are controversial foods. Limiting the consumption of these foods (twice a month or less) is recommended, despite the potential human health benefits of soy in the prevention of cancer, cardiovascular diseases, the reduction of menopause symptoms, increased bone-mineral density, and decreased insulin resistance. Conversely, soy has raised concern about thyroid gland function. Some studies report the literature provides little evidence that the consumption of soy foods or isoflavones has adverse effects for euthyroid individuals with iodine deficiency. However, there is a theoretical concern based on in vitro and animal studies that individuals with impaired thyroid function and/or whose iodine intake is marginal are more likely to develop hypothyroidism with soy consumption. Thus, it is vital that consumers of soy-based foods be sure that their iodine intake is adequate. In addition, soy may hinder the absorption of thyroid drugs.
Limiting the consumption of alcohol (once a month or less) is recommended.