The cruciferous family of vegetables, also called brassicas, have been demonized for years as a cause of hypothyroidism. These foods are sometimes classified as goitrogens because over-consumption of these foods appears to block thyroid peroxidase (TPO), causing the thyroid to grow more thyroid tissue resulting in a goiter.
These foods contain sulfur-containing compounds called glucosinolates and when chewed are broken down (through hydrolysis) into biologically active, cancer-fighting antioxidants. Two of these compounds classified as goitrogenic are isothiocyanates and thiocyanates. However, there is little evidence that it’s the consumption of these otherwise healing compounds alone that cause the problem. It appears that they only interfere with TPO when there is a deficiency in iodine or selenium and other antioxidants.1
The truth is that foods from the brassica family are rich in antioxidants and eating them along with adequate iodine and selenium has been proven to reduce inflammation and reduce the risk of cancer—even thyroid cancer.2 Consumption of isothiocyanates along with selenium has been shown to boost glutathione peroxidase3 (a powerful antioxidant), which I talk about in Chapter 17 of The Thyroid Cure: Restore Your Liver.
As long as you correct any nutritional deficiencies you may have, you should have no reason to worry about these foods affecting your thyroid. If you are taking thyroid hormone replacement, these foods will not interfere with the action of these hormones. Remember that cooking and steaming reduces the goitrogenic (along with some of the antioxidant) properties of these foods.
However, if you feel these foods exacerbate your symptoms then please listen to your body. After all you are the one who knows your body the best. Ideally, when your antibodies are gone and you begin to wean off your medication, you will no longer be deficient in selenium, iodine or zinc and you may eat abundantly from this family of foods!
- Boyages S. Progress in Understanding the Clinical Consequences of Endemic Iodine Deficiency. Current Opinion in Endocrinology, Diabetes and Obesity 4.5 (1997): 320-327. http://www.researchgate.net/publication/232133920_Progress_in_understanding_the_clinical_consequences_of_endemic_iodine_deficiency
- Keck AS, Finley JW. Cruciferous Vegetables: Cancer Protective Mechanisms of Glucosinolate Hydrolysis Products and Selenium. Integr Cancer There March 2004 3: 5-12 http://www.ncbi.nlm.nih.gov/pubmed/15035868 –
- Barrera LN, Cassidy A, Wang W, et al. TrxR1 and GPx2 are potently induced by isothiocyanates and selenium, and mutually cooperate to protect Caco-2 cells against free radical-mediated cell death. Biochimica et Biophysica Acta (BBA) – Molecular Cell Research. Oct 2012, Vol. 1823, No. 10: 1914-192 http://www.ncbi.nlm.nih.gov/pubmed/22820176