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Goitrogens are foods which suppress thyroid function. In normals, goitrogens can induce hypothyroidism and goiter. In hypos, goitrogens can further depress thyroidal function and stimulate the growth of the thyroid (goiter).

In hyperthyroids, goitrogens may help suppress thyroidal function until normal thyroidal functioning can be restored. However, this may not be a good strategy. Goitrogens work by interfering with the thyroidal uptake of iodine. While many hypers try to limit thyroid output by iodine restriction, this strategy can backfire. Iodine restriction will cause the thyroid to increase in size (goiter) in an effort to filter more blood to get more iodine. When iodine is then re-introduced to the diet or accidentally ingested, the now larger thyroid gland has the capacity for greater thyroid hormone production.

I do not believe that iodine restriction is a good long-term method for controlling thyroid hormone production. Therefore the consumption of goitrogens is not a good strategy. It is better to increase copper metabolism by supplementation of copper and the assisting nutrients. Once copper is replenished and copper metabolism is working properly, the body will tolerate iodine without increasing thyroid hormone production.

Many goitrogens are generally members of the brassica family. These include:

Brussel Sprouts

Rape seed (Canola Oil)

Other goitrogens include: 

Pine nuts

Brassica family vegetables not only inhibit thyroid production, but they also inhibit cancer growth. We know that sulfur, copper, and iron work closely together and that excessive sulfur can deplete copper and/or iron. The following study mentions that excessive kale consumption will cause anemia in cattle. Generally anemia is the result of low iron and/or copper. Also, foods and drugs that cause anemia also reduce cancer growth, indicating that the brassica vegetables might reduce cancer by inducing anemia.

Because copper and iron are so important for thyroid function, I don't think that it is advisable to eat plants of the brassica family. We have seen that the primary pre-condition for the production of thyroid disease is the onset of anemia. Brassica vegetables, with their high sulfur content, may be foods which induce anemia and consequently thyroid disease. Don't consider this the final word on these vegetables, but we will continue to look at this possibility.

Food Chem Toxicol 1995 Jun;33(6):537-43

Bioactive organosulfur phytochemicals in Brassica oleracea vegetables--a review.

Stoewsand GS.

Department of Food Science and Technology, New York State Agricultural Experiment Station, Cornell University, Geneva 14456, USA.

Sulfur-containing phytochemicals of two different kinds are present in all Brassica oleracea (Cruciferae) vegetables (cabbage, broccoli, etc.). They are glucosinolates (previously called thioglucosides) and S-methyl cysteine sulfoxide. These compounds, which are derived in plant tissue by amino acid biosynthesis, show quite different toxicological effects and appear to possess anticarcinogenic properties. Glucosinolates have been extensively studied since the mid-nineteenth century. They are present in plant foods besides Brassica vegetables with especially high levels in a number of seed meals fed to livestock. About 100 different kinds of glucosinolates are known to exist in the plant kingdom, but only about 10 are present in Brassica. The first toxic effects of isothiocyanates and other hydrolytic products from glucosinolates that were identified were goitre and a general inhibition of iodine uptake by the thyroid. Numerous studies have indicated that the hydrolytic products of at least three glucosinolates, 4-methyl-sulfinylbutyl (glucoraphanin), 2-phenylethyl (gluconasturtiin) and 3-indolylmethyl (glucobrassicin), have anticarcinogenic activity. Indole-3-carbinol, a metabolite of glucobrassicin, has shown inhibitory effects in studies of human breast and ovarian cancers. Kale poisoning, or a severe haemolytic anaemia, was discovered in cattle in Europe in the 1930s, but its link with the hydrolytic product of S-methyl cysteine sulfoxide was only shown about 35 years later. S-methyl cysteine sulfoxide and its metabolite methyl methane thiosulfinate were shown to inhibit chemically-induced genotoxicity in mice. Thus, the cancer chemopreventive effects of Brassica vegetables that have been shown in human and animal studies may be due to the presence of both types of sulfur-containing phytochemicals (i.e. certain glucosinolates and S-methyl cysteine sulfoxide).


Eur J Endocrinol 1994 Aug;131(2):138-44

Antithyroid effects in vivo and in vitro of babassu and mandioca: a staple food in goiter areas of Brazil.

Gaitan E, Cooksey RC, Legan J, Lindsay RH, Ingbar SH, Medeiros-Neto G

University of Mississippi School of Medicine, Jackson.

Babassu (Orbignya phalerata), a palm-tree coconut fruit, mixed with mandioca (Manihot utilissima) is the staple food of people living in the endemic goiter area of Maranhao in Brazil, where goiter prevalence among schoolchildren was still 38% in 1986 despite an adequate iodine intake in most of the population. Therefore, the question arose as to whether or not the ingestion of babassu alone or mixed with mandioca contributed to the persistence of endemic goiter in this area of Brazil. In this investigation we examined the potential antithyroid effects of babassu and mandioca by means of in vivo studies in Sprague-Dawley rats, in vitro studies in porcine thyroid slices and using a purified porcine thyroid peroxidase (TPO) system. Samples of various edible parts of babassu and mandioca flour were homogenized and extracted in goitrogen-free water (GFW) for in vivo experiments, and in methanol (100 g/l), GFW or 0.06 mol/l phosphate buffer (pH 7.0) for in vitro experiments. The edible parts of babassu produced significant in vivo antithyroid effects (p < 0.05- < 0.001) in rats on a high iodine intake (14 micrograms I- day-1.rat-1), as well as distinct and reproducible antithyroid and anti-TPO activities in both in vitro systems, their action being similar to that of the thionamide-like antithyroid drugs propylthiouracil and methimazole.