Hypothyroidism and Goitrogens

By: Claire Georgiou, Reboot Naturopath, B.HSc ND

A question that has come up often on our community page Ask the Nutritionist is ‘what fruits and vegetables should I avoid if I have a thyroid condition?’ It has been shown that some vegetables can interfere with the way thyroid hormones are manufactured by the thyroid gland.

Your thyroid is a butterfly-shaped gland that sits near your vocal cords and produces thyroid hormones that control your metabolism. Symptoms of an under active thyroid gland can be low body temperature, constipation, weight gain, hair loss, dry flaky skin and nails, fluid retention, slow reflexes, fatigue and slow thoughts and cognition. Thyroid problems can develop for a number of reasons, but the most common causes of thyroid problems are nutrient deficiencies such as iodine and selenium deficiency, autoimmune disease, genetics, stress and environmental factors. The most common type of thyroid problem is hypothyroidism (under active gland).

Goitrogens are substances that suppress the function of the thyroid gland by interfering and blocking the enzyme that allows your thyroid to use iodine, this can cause an enlargement of the thyroid (goitre). Iodine is important in the formation of thyroid hormone. So by inhibiting iodine, there will be a decrease in thyroid hormone.** Iodine deficiency has re-emerged in Australia in recent years.

If your diet is deficient in iodine and/or selenium, or you have an underactive thyroid, known as hypothyroidism, eating raw cruciferous vegetables can further suppress your thyroid hormone function. So it is suggested to avoid consuming LARGE amounts of RAW cruciferous vegetables such as broccoli, cauliflower, Brussels sprouts, bok choy, broccolini, chinese cabbage, kale, kohlrabi, radish, mustard greens, collard greens, choy sum, horseradish and turnips. Isothiocyanates are the category of substances in cruciferous vegetables that have been associated with decreased thyroid function.

Soy contains goitrogens, although fermenting soy disables the goitrogenic isoflavones found in soy foods. Other foods containing smaller amounts are spinach, strawberries, peaches and peanuts.

It remains important to consume the foods listed above for their health promoting properties at least a few times per week. Cruciferous vegetables have been shown in studies to decrease the risk of many types of cancer, particularly bowel and breast cancer. Cruciferous vegetables are high in vitamins, minerals and phyto-nutrients. The American Cancer Society suggests eating one serving of cruciferous vegetables every day.

During your Reboot, the goal is not to eliminate goitrogenic foods from the meal plan, but to limit intake so that it falls into a reasonable range.

Since cooking has been shown to inactivate the goitrogenic compounds, for individuals with deficient thyroid hormone production, cooking of cruciferous vegetables is highly recommended. Isothiocyanates found in cruciferous vegetables appear to be heat-sensitive, and cooking appears to lower the availability of these substances. Avoid consuming these goitrogenic vegetables in a juice, as the goitrogenic properties are fully intact in their raw state. You can consume small amounts raw in a meal, but it is advised to consume the majority of these vegetables cooked. 

It is very important to note that if you have a normal thyroid function and consume adequate amounts of iodine, these compounds will have no effect on your thyroid.

Food sources of iodine include iodized sea salt, seaweed, saltwater fish, shellfish and eggs. Food sources of selenium are brazil nuts, sunflower seeds, garlic, mushroom, onions and seafood.

A Thyroid Juice
1 Apple
½ cup Pineapple
½ Beetroot with tops
2 Stalks Celery
1 Carrot

Other Substititions for cruciferious vegetables: celery, celery leaves, silverbeet (chard), beetroot (beet), beetroot leaves, cos (romaine) lettuce, Courgette (zucchini), cucumber, grapefruit, lemon, limes, orange and watermelon to name a few.

REFERENCES
http://www.livestrong.com/article/494669-anti-goitrogenic-diet-for-hypothyroidism/#ixzz1l12PuKiT
http://www.whfoods.com/genpage.php?tname=george&dbid=47
http://en.wikipedia.org/wiki/Goitrogens
PubMed: Hypothyroidism
Diet.com: Iodine
http://www.liverdoctor.com/index.php?page=is-your-thyroid-gland-letting-you-down
http://en.wikipedia.org/wiki/Hypothyroidism
http://www.nutritionaustralia.org/national/resource/iodine-facts
http://en.wikipedia.org/wiki/Selenium

Comments:

Most cruciferious vegetables are eaten cooked. Other foods that contain goitrogens include flax seed and garlic. Usually there is no problems with eating these because they are used in such small quantities. Garlic is usually cooked as well.

If you do not have low thyroid function there is no reason why you should avoid these otherwise extremely healthy foods.