Can Vegetables Put Your Thyroid Health at Risk?

Written by Katherine M. Coleman, M.N.T.

Recently a patient inquired if eating raw dark leafy vegetables and raw cruciferous vegetables could contribute to thyroid problems because they are considered by some to be “goitrogenic foods.” It is actually scientifically inaccurate to classify a group of foods as goitrogenic, as goitrogens are not a category of substances like proteins, carbs, fats, etc.

Cruciferous vegetables contain higher amounts of isothiocyanates, commonly made in the body from other phytonutrients, which, if consumed in high quantities alongside a selenium deficiency, have been shown to contribute to thyroid dysfunction. However there is no correlation between daily intake of cruciferous vegetables in ordinary amounts and risk to the thyroid.

Additionally, many vegetables including the dark leafy greens contain isoflavones, a flavonoid that at a molecular and biochemical level may interfere with an enzyme known as thyroid peroxidase (TPO). TPO helps attach iodine to an amino acid called tyrosine and this iodine-tyrosine combination forms the basis for production of thyroid hormones. It’s known that most flavonoids possess the ability to interfere with TPO, although research findings on isoflavones show a limited impact on thyroid function.

In summation, the health consequences of raw dark leafy and cruciferous vegetables do not outweigh their benefits, and cannot be deemed automatic or guaranteed, but rather may be dependent upon the contribution of supplementary health conditions, such as an iodine or selenium deficiency. If you are still concerned about isothiocyanates and isoflavones, know that cooking inactivates the goitrogenic substances in both by as mush as one third because these compounds are heat sensitive.

References:
Dal Maso L, Bosetti C, La Vecchia C et al. Risk factors for thyroid cancer: an epidemiological review focused on nutritional factors. Cancer Causes Control. 2009 Feb;20(1):75-86.
de Souza dos Santos MC, Goncalves CFL, Vaisman M et al. Impact of flavonoids on thyroid function. Food and Chemical Toxicology, Volume 49, Issue 10, October 2011, Pages 2495-2502.
Doerge DR and Chang HC. Inactivation of thyroid peroxidase by soy isoflavones, in vitro and in vivo. Journal of Chromatography B, Volume 777, Issues 1â “2, 25 September 2002, Pages 269-279.
Vanderpas J. Nutritional epidemiology and thyroid hormone metabolism. Annu Rev Nutr. 2006;26:293-322.

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