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The Seaweed Gatherers, Paul Gaugin
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Iodine Research
Resource Network of The Iodine Movement
GOITROGENS
GOITROGENIC FOODS - pg 1
(continued on pg 2 )
(return to overview)
There are two primary categories of food that are commonly seen as goitrogenic: (1) soy products
and (2) vegetables of the Brassica family (e.g., broccoli, cauliflower, kale, cabbage, collard greens,
kohlrabi, radish, turnips, mustard greens, Brussels sprouts, and rutabagas).
Soy
Brassica
Other foods
Factors mediating the effects of goitrogens
Other effects of goitrogens
Goitrogen Research
Chandra, et al have researched plants containing cyanogenic goitrogens (glucosinolates,
glucosides, and thiocyanates). When studying radishes (a cruciferous plant containing cyanogenic
goitrogens), they found (1) increased weight of the thyroid gland, (2) decreased thyroid peroxidase
activity, (3) reduced thyroid hormone profiles and (4) elevated level of thyrotropin -- even after
supplementation of adequate iodine.
Daniel has written a highly recognized book on soy that includes useful information on the
goitrogens found in soy: isoflavones and saponins.
Doerge has established that soy isoflavones and many dietary flavonoids inhibit TPO.
Gaitan, et al, have researched a variety of antithyroid compounds and environmental goitrogens.
They have presented strong evidence that C-glycosylflavones in millet inhibits TPO. They have
investigated antithyroid effects of babassu and mandioca and the goitrogenic effects of coal-water
extracts. They have also looked at the antigoitrogenic effect of casein.
Mary Shomon has written on the glucosinolates in vegetables that act as goitrogens.
Masterjohn discusses goitrogenic foods, including soy, millet, cruciferous vegetables, cassava,
lima beans, flax seeds, almonds, and fruits and fruit seeds of the Rosacea family. Especially
interesting is his discussion of the effects of cooking and fermenting.
Elnour discusses millet as a goitrogen.
Kaplan discusses the goitrogens that create problems for green iguanas.
CHANDRA
Effect of radish (Raphanus sativus Linn.) on thyroid status under conditions of varying iodine intake
in rats.
Chandra AK, Mukhopadhyay S, Ghosh D, Tripathy S.
Indian J Exp Biol. 2006 Aug;44(8):653-61.
[abstract only]
Cruciferous plants viz. cabbage, cauliflower, turnip, radish, mustard etc. that contain
goitrogenic/antithyroid substances, constitute a portion of regular human diet. The effect of chronic
feeding of fresh and cooked radish, R. sativus under varying state of iodine intake on
morphological and functional status of thyroid in albino rats was evaluated by thyroid gland
morphology and histology, thyroid peroxidase activity, serum triiodothyronine, thyroxine and
thyrotropin levels. The consumption pattern of iodine and goitrogens of cyanogenic origin was
evaluated by measuring urinary iodine and thiocyanate levels respectively. After chronic radish
feeding, increased weight of thyroid gland, decreased thyroid peroxidase activity, reduced thyroid
hormone profiles and elevated level of thyrotropin were observed resembling a relative state of
hypoactive thyroid gland in comparison to control even after supplementation of adequate iodine.
Goitrogenic content of Indian cyanogenic plant foods & their in vitro anti-thyroidal activity.
Chandra AK, Mukhopadhyay S, Lahari D, Tripathy S.
Indian J Med Res. 2004 May;119(5):180-5.
BACKGROUND & OBJECTIVES: Consumption of cyanogenic foods has been considered as one of
the etiological factors in certain instances for the persistence of endemic goitre. The present study
was undertaken to study the cyanogenic glucosides, glucosinolates and thiocyanate content in
edible portion of certain selected plant foods of Indian origin. Further in vitro anti-thyroidal activity
using raw, boiled and cooked extracts of these plants with and without excess iodide was also
studied. METHODS: Cyanogenic plant foods generally vegetables were collected from different
areas of West Bengal and Tripura. Cassava was obtained from Meghalaya and Kerala and their
cyanogenic glucosides, glucosinolates and thiocyanate were estimated. Thyroid peroxidase activity
(TPO) of human thyroid was assayed from microsomal fraction following I3- from iodide. The anti-
TPO activities of the plants were assayed after adding raw, boiled and cooked extracts in the assay
medium with and without extra iodide. Relative antithyroidal potency of the plant extracts was also
evaluated in terms of the concentration (IC50) necessary to produce 50 per cent inhibition of TPO
activity. PTU equivalence of the plant foods was also determined. RESULTS: Cabbage and
cauliflower were rich in glucosinolates, bamboo shoot and cassava were rich in cyanogenic
glucosides, mustard, turnip and radish were relatively rich in thiocyanate however all the
constituents were present in each plant. Boiled extracts showed maximum inhibition of TPO activity
followed by cooked and raw extracts. Excess iodide was found relatively effective for raw extract but
less effective for boiled and cooked extracts in reversing anti-TPO activity. Inhibition constant
(IC50) was found highest with bamboo shoot and least with cabbage. INTERPRETATION &
CONCLUSION: Raw, boiled and cooked extracts of the plants showed anti-thyroidal activity in vitro.
Excess iodide reversed the anti-TPO activity to same extent but could not neutralise it.
Effect of bamboo shoot, Bambusa arundinacea (Retz.) Willd. on thyroid status under conditions of
varying iodine intake in rats.
Chandra AK, Ghosh D, Mukhopadhyay S, Tripathy S.
Indian J Exp Biol. 2004 Aug;42(8):781-6.
[abstract only]
Young shoots or sprouts of common bamboos are used as food in third world countries. Evidences
suggest the presence of cyanogenic glucoside like anti-thyroidal substance in bamboo shoots (BS)
but effect of prolonged BS consumption on thyroid status under conditions of varying iodine
nutriture remains unexplored. The study was undertaken to evaluate goitrogenic content, in vitro
anti thyroid peroxidase (TPO) activity and in vivo anti thyroid potential of BS with and without extra
iodide. Fresh BS contains high cyanogenic glucoside (551 mg/kg), followed by thiocyanate
(24mg/kg) and glucosinolate (9.57mg/kg). In vitro inhibition in TPO activity was found with raw, raw
boiled and cooked extracts. Inhibition constant (IC50) and PTU equivalence of fresh BS were 27.5
+/-0.77 microg and 3.27 respectively. Extra iodide in the incubation media reduced TPO inhibition
induced by BS but could not cancel it. Thyroid weight, TPO activity and total serum thyroid
hormone levels of BS fed animals for 45 and 90 days respectively were determined and compared
with controls. Significant increase in thyroid weight as well as higher excretion of thiocyanate and
iodine along with marked decrease in thyroid peroxidase activity, T4 and T3 levels were observed
in BS fed group. Chronic BS consumption gradually developed a state of hypothyroidism. Extra
iodide had reduced the anti-thyroidal effect of BS to an extent but could not cancel it because of
excessive cyanogenic glucoside, glucosinolate and thiocyanate present in it.
Dietary supplies of iodine and thiocyanate in the etiology of endemic goiter in Tripura.
Chandra AK, Ray I.
Indian J Pediatr. 2001 May;68(5):399-404.
[abstract only]
In the post-salt iodization phase, a study on iodine nutriture status was conducted in Tripura of
North East India. The clinical variable of the study was goiter and the biochemical variables were
urinary iodine and thiocyanate. Random sampling methodology was followed for selecting the study
areas in the State. In each study area, the studied population consisted of school children of both
sexes in the age group 6-15 years. The total study areas were 22 and the total number of the
population was 10,801. The total number of urine samples were analysed for iodine and
thiocyanate were 1,032 (about 10%). The total goiter rate was 21.63%. Population of most of the
studied areas had no biochemical iodine deficiency as evidenced by median urinary iodine
excretion levels. However, the per capita consumption of iodine of about 40% population was
inadequate. A large number of cyanogenic plants (SCN precursors) are used as common
vegetables. This study ensures that the existing goiter prevalence in the region could possibly due
to non-uniform adequate iodine supply along with the thiocyanate load.
DANIEL
The whole soy story: the dark side of America's favorite health food.
Daniel KT
Book. New Trends Publishing, Inc, 2005
Soy foods always enter the body carrying their cargo of other anti-nutritional factors--saponins,
soyatoxin, phytates, protease inhibitors, oxalates, goitrogens and estrogens, all of which have
shown the potential to cause harm." (p 236)
Although the best known goitrogens in soy are the isoflavones, the Japanese researcher Shuichi
Kimura discovered back in the mid-1970s that saponins can also spur enlargement of the thyroid."
(p 240)
Soybeans contain goitrogens. Goitrogens are substances that block the synthesis of thyroid
hormones. As their name suggest, they can cause goiter, which is a pronounced swelling in the
neck caused by an enlarged thyroid gland." (p 311)
Soy is not the only goitrogenic food. Broccoli, cabbage, Brussels sprouts, cassava, rapeseed,
turnips, mustard, radish, peanuts and millet also contain goitrogens. However, few adults--and
even fewer children--eat these foods to excess. Furthermore, the goitrogens in most of these
foods are easily neutralized by cooking or fermentation.
Soy foods are different. The principal goitrogens in soybeans are the estrogenic plant hormones
known as isoflavones. The antinutrients known as saponins in soy may also be goitrogens....
Cooking and processing methods using heat, pressure and alkaline solutions will neither deactivate
nor remove isoflavones or saponins. Only solvent extraction can do that. So far, the soy industry
has resisted using these processes--even for soy destined for babies, who are highly vulnerable to
their estrogenic and goitrogenic effects." (pp 311-2)
The causes of so much thyroid disease appear to be many and synergistic. Radiation, mercury,
fluoride, plastics, pesticides, dioxins, solvents and estrogens (and estrogen mimickers) found in
commercial meats, plastics and hormone replacement therapies (HRT) have all been implicated.
And so has soy.
The United Kingdom's Committee on Toxicity (COT) has identified several populations at special
risk for soy-induced thyroid disease--infants on soy formula, vegans who use soy as their principal
meat and dairy replacements, and men and women who are self medicating with soy foods and/or
isoflavone supplements in an attempt to prevent or reverse menopausal symptoms, cancer or high
cholesterol. As early as 1980, British government researchers pointed out that soy-consuming
vegans were at risk." (pp 313-4)
Although iodine deficiency increases the antithyroid effects of goitrogenic foods, iodine sufficiency
does not offer complete protection in the face of high soy consumption." (p 315)
The first report in medical journals of enlarged thyroid glands in rats and chickens fed soybean
rations appeared in the 1930s. In 1961, researchers discovered that spiking the chow with iodine
could prevent goiter. But this quick-fix solution to a serious problem turned out to be simplistic.
Rats and chickens fed soybean-based chows required twice as much iodine to prevent thyroid
enlargement as animals fed soy free diets. Even then, their thyroid glands showed abnormal cell
proliferation. When iodine is largely absent, soy can provoke malignant hyperplastic goiter.
Dr. Mieko Kimura of Kyoto University writes: "It is well known that a goiter is induced by simple
iodine deficiency, but it was noteworthy that hyperplastic goiters can be induced in rats in a high
percentage by the administration of soybean factor(s) under iodine-deficient conditions, together
with accurate signs of malignancy such as invasiveness and metastasis formation in the lungs." (p
315)
Likewise, the soy estrogens known as the isoflavones can inhibit the action of thyroid drugs. to
ensure their efficacy, many health professionals recommend that they not be taken at the same
time as food or supplements high in soy." (p 316)
Boosting the thyroid with drugs like Synthroid, then depressing it with thyroid inhibitors like soy
foods or isoflavone supplements can put extreme stress on the thyroid. Environmental scientist
Mike Fitzpatrick, Ph.D., points out that this is the classic way that researchers induce thyroid tumors
in laboratory animals. The fact that soy is "natural" does not make it safe or weak. A serving of
soy food provides up to three times the goitrogenic potency of the pharmaceutical thyroid-inhibiting
drugs methimazole and 6-propylthiouracil." (p 316)
Mechanisms of action. Plant estrogens interact with the thyroid gland in several ways. Genistein
and daidzein (the key isoflavones in soy) and biochanin A (found in clover and alfalfa) are potent
inhibitors of thyroid peroxidase (TPO), an enzyme involved in the synthesis of T3 and T4. In vitro
experiments have shown that soy isoflavone's inhibition of thyroid peroxidase interferes with a
critical stage in thyroid hormone production--the iodinization of the amino acid tyrosine.
This interference occurs whether or not sufficient or extra iodine is present. As a result, the body
produces useless mono-, di- and tri-iodoisoflavones and not the mono, di, and tri and quarto forms
of thyroid hormone. In the human body, this interference can cause a drop in thyroid hormone
levels, an increase in thyroid stimulating hormone and stress on the thyroid gland." (p 317)
Another way goitrogens damage thyroid function is by increasing concentrations of thyroid binding
globulin (TBG), a plasma protein involved in the inactivation and transport of T3 and T4. This
lowers free thyroxine concentrations and increases TSH secretions." (pp 317-8)
The first reports of thyroid damage suffered by human infants on soy formula appeared during the
1950s. Most cases involved goiter, with no overt signs of hypothyroidism. Although iodine
supplements helped, they did not entirely solve the problem. Researchers found that matters
improved considerably if the processing of the soy formula included extraction with an organic
solvent as well as heating. Although no one at the time identified the principal goitrogens as the
isoflavones, alcohol solvent extraction is, in fact, the only way to remove them. Heat, pressure and
alkaline treatments used in ordinary soy processing will not remove the isoflavones." (p 318)
Autoimmune thyroid disease is far more likely to occur in children who were fed soy formula." (p
318)
The most powerful evidence of soy's adverse effects on the adult thyroid emerged from a study
carried out at the Ishizuki Thyroid Clinic in Japan. Dr. Yoshimochi Ishizuki of Aichi Medical
University demonstrated that 30 grams of pickled soybeans per day, given to healthy adult men
and women, induced thyroid disruptions in only 30 days. All subjects consumed seaweed daily to
ensure adequate iodine intake." (p 320)
Soy eaters are at risk for thyroid damage not only because of the goitrogens in soy but also
because phytates contribute to zinc deficiency and an "anti-vitamin factor" results in greater needs
of the body for vitamin B-12." (pp 322-3)
Soybeans naturally contain goitrogens, allergens, protease inhibitors and other antinutrients and
toxins that damage the digestive, immune and neuroendocrine systems, putting consumers at
increased risk for many health problems, including cancer." (p 381)
The Whole Soy Story -- Website
GOITROGENIC FOODS - pg 1
(continued on pg 2 )
(return to overview)
There are two primary categories of food that are commonly seen as goitrogenic: (1) soy products
and (2) vegetables of the Brassica family (e.g., broccoli, cauliflower, kale, cabbage, collard greens,
kohlrabi, radish, turnips, mustard greens, Brussels sprouts, and rutabagas).
Soy
- Isoflavones -- especially genistein -- in soy block TPO (Thyroid Peroxidase), an enzyme
critical to the transformation process that results in the creation of thyroid hormones from
iodide.
Brassica
- Isothiocyanates in the Brassica vegetables also block TPO. The cyanogenic glucosides,
glucosinolates, and thiocyanates all seem to be important. Thiocyanates block the NIS
symporter, interfering with iodide uptake to the thyroid and breast (keeping the iodide from
the breast milk).
Other foods
- A variety of other foods are also generally seen as goitrogens: e.g., millet, rape seed
(Canola Oil), pine nuts, peanuts, cassava, bamboo shoots.
Goitrogens are also found in clover and alfalfa (biochanin A -- a TPO inhibitor), grasses, and
water. Goitrogens eaten by animals can affect the iodine in animal products such as milk,
butter, cheese, eggs, meat, etc.
Factors mediating the effects of goitrogens
- Unfortunately, research has not yet firmly established exactly what compounds are
goitrogenic, how they operate, and how best to deactivate them.
Cooking seems to reduce the chemicals in the Brassica family, but does not eliminate them.
Fermentation is also thought to affect these chemicals, but it is not clear exactly what is
happening nor how effective it is.
The effects of these chemicals is significantly worse if iodine is deficient. However, adequate
iodine does not seem to completely protect against them.
Moreover, the effects on TPO do not seem to fully explain what is happening, since blocked
TPO does not always result in reduced thyroid function.
Other effects of goitrogens
- In addition to their effects on goiter, hypothyroidism, and hyperthyroidism, goitrogenic foods
also appear to be related to thyroid cancer and autoimmune thyroid diseases (Fort).
Goitrogen Research
Chandra, et al have researched plants containing cyanogenic goitrogens (glucosinolates,
glucosides, and thiocyanates). When studying radishes (a cruciferous plant containing cyanogenic
goitrogens), they found (1) increased weight of the thyroid gland, (2) decreased thyroid peroxidase
activity, (3) reduced thyroid hormone profiles and (4) elevated level of thyrotropin -- even after
supplementation of adequate iodine.
Daniel has written a highly recognized book on soy that includes useful information on the
goitrogens found in soy: isoflavones and saponins.
Doerge has established that soy isoflavones and many dietary flavonoids inhibit TPO.
Gaitan, et al, have researched a variety of antithyroid compounds and environmental goitrogens.
They have presented strong evidence that C-glycosylflavones in millet inhibits TPO. They have
investigated antithyroid effects of babassu and mandioca and the goitrogenic effects of coal-water
extracts. They have also looked at the antigoitrogenic effect of casein.
Mary Shomon has written on the glucosinolates in vegetables that act as goitrogens.
Masterjohn discusses goitrogenic foods, including soy, millet, cruciferous vegetables, cassava,
lima beans, flax seeds, almonds, and fruits and fruit seeds of the Rosacea family. Especially
interesting is his discussion of the effects of cooking and fermenting.
Elnour discusses millet as a goitrogen.
Kaplan discusses the goitrogens that create problems for green iguanas.
CHANDRA
Effect of radish (Raphanus sativus Linn.) on thyroid status under conditions of varying iodine intake
in rats.
Chandra AK, Mukhopadhyay S, Ghosh D, Tripathy S.
Indian J Exp Biol. 2006 Aug;44(8):653-61.
[abstract only]
Cruciferous plants viz. cabbage, cauliflower, turnip, radish, mustard etc. that contain
goitrogenic/antithyroid substances, constitute a portion of regular human diet. The effect of chronic
feeding of fresh and cooked radish, R. sativus under varying state of iodine intake on
morphological and functional status of thyroid in albino rats was evaluated by thyroid gland
morphology and histology, thyroid peroxidase activity, serum triiodothyronine, thyroxine and
thyrotropin levels. The consumption pattern of iodine and goitrogens of cyanogenic origin was
evaluated by measuring urinary iodine and thiocyanate levels respectively. After chronic radish
feeding, increased weight of thyroid gland, decreased thyroid peroxidase activity, reduced thyroid
hormone profiles and elevated level of thyrotropin were observed resembling a relative state of
hypoactive thyroid gland in comparison to control even after supplementation of adequate iodine.
Goitrogenic content of Indian cyanogenic plant foods & their in vitro anti-thyroidal activity.
Chandra AK, Mukhopadhyay S, Lahari D, Tripathy S.
Indian J Med Res. 2004 May;119(5):180-5.
BACKGROUND & OBJECTIVES: Consumption of cyanogenic foods has been considered as one of
the etiological factors in certain instances for the persistence of endemic goitre. The present study
was undertaken to study the cyanogenic glucosides, glucosinolates and thiocyanate content in
edible portion of certain selected plant foods of Indian origin. Further in vitro anti-thyroidal activity
using raw, boiled and cooked extracts of these plants with and without excess iodide was also
studied. METHODS: Cyanogenic plant foods generally vegetables were collected from different
areas of West Bengal and Tripura. Cassava was obtained from Meghalaya and Kerala and their
cyanogenic glucosides, glucosinolates and thiocyanate were estimated. Thyroid peroxidase activity
(TPO) of human thyroid was assayed from microsomal fraction following I3- from iodide. The anti-
TPO activities of the plants were assayed after adding raw, boiled and cooked extracts in the assay
medium with and without extra iodide. Relative antithyroidal potency of the plant extracts was also
evaluated in terms of the concentration (IC50) necessary to produce 50 per cent inhibition of TPO
activity. PTU equivalence of the plant foods was also determined. RESULTS: Cabbage and
cauliflower were rich in glucosinolates, bamboo shoot and cassava were rich in cyanogenic
glucosides, mustard, turnip and radish were relatively rich in thiocyanate however all the
constituents were present in each plant. Boiled extracts showed maximum inhibition of TPO activity
followed by cooked and raw extracts. Excess iodide was found relatively effective for raw extract but
less effective for boiled and cooked extracts in reversing anti-TPO activity. Inhibition constant
(IC50) was found highest with bamboo shoot and least with cabbage. INTERPRETATION &
CONCLUSION: Raw, boiled and cooked extracts of the plants showed anti-thyroidal activity in vitro.
Excess iodide reversed the anti-TPO activity to same extent but could not neutralise it.
Effect of bamboo shoot, Bambusa arundinacea (Retz.) Willd. on thyroid status under conditions of
varying iodine intake in rats.
Chandra AK, Ghosh D, Mukhopadhyay S, Tripathy S.
Indian J Exp Biol. 2004 Aug;42(8):781-6.
[abstract only]
Young shoots or sprouts of common bamboos are used as food in third world countries. Evidences
suggest the presence of cyanogenic glucoside like anti-thyroidal substance in bamboo shoots (BS)
but effect of prolonged BS consumption on thyroid status under conditions of varying iodine
nutriture remains unexplored. The study was undertaken to evaluate goitrogenic content, in vitro
anti thyroid peroxidase (TPO) activity and in vivo anti thyroid potential of BS with and without extra
iodide. Fresh BS contains high cyanogenic glucoside (551 mg/kg), followed by thiocyanate
(24mg/kg) and glucosinolate (9.57mg/kg). In vitro inhibition in TPO activity was found with raw, raw
boiled and cooked extracts. Inhibition constant (IC50) and PTU equivalence of fresh BS were 27.5
+/-0.77 microg and 3.27 respectively. Extra iodide in the incubation media reduced TPO inhibition
induced by BS but could not cancel it. Thyroid weight, TPO activity and total serum thyroid
hormone levels of BS fed animals for 45 and 90 days respectively were determined and compared
with controls. Significant increase in thyroid weight as well as higher excretion of thiocyanate and
iodine along with marked decrease in thyroid peroxidase activity, T4 and T3 levels were observed
in BS fed group. Chronic BS consumption gradually developed a state of hypothyroidism. Extra
iodide had reduced the anti-thyroidal effect of BS to an extent but could not cancel it because of
excessive cyanogenic glucoside, glucosinolate and thiocyanate present in it.
Dietary supplies of iodine and thiocyanate in the etiology of endemic goiter in Tripura.
Chandra AK, Ray I.
Indian J Pediatr. 2001 May;68(5):399-404.
[abstract only]
In the post-salt iodization phase, a study on iodine nutriture status was conducted in Tripura of
North East India. The clinical variable of the study was goiter and the biochemical variables were
urinary iodine and thiocyanate. Random sampling methodology was followed for selecting the study
areas in the State. In each study area, the studied population consisted of school children of both
sexes in the age group 6-15 years. The total study areas were 22 and the total number of the
population was 10,801. The total number of urine samples were analysed for iodine and
thiocyanate were 1,032 (about 10%). The total goiter rate was 21.63%. Population of most of the
studied areas had no biochemical iodine deficiency as evidenced by median urinary iodine
excretion levels. However, the per capita consumption of iodine of about 40% population was
inadequate. A large number of cyanogenic plants (SCN precursors) are used as common
vegetables. This study ensures that the existing goiter prevalence in the region could possibly due
to non-uniform adequate iodine supply along with the thiocyanate load.
DANIEL
The whole soy story: the dark side of America's favorite health food.
Daniel KT
Book. New Trends Publishing, Inc, 2005
Soy foods always enter the body carrying their cargo of other anti-nutritional factors--saponins,
soyatoxin, phytates, protease inhibitors, oxalates, goitrogens and estrogens, all of which have
shown the potential to cause harm." (p 236)
Although the best known goitrogens in soy are the isoflavones, the Japanese researcher Shuichi
Kimura discovered back in the mid-1970s that saponins can also spur enlargement of the thyroid."
(p 240)
Soybeans contain goitrogens. Goitrogens are substances that block the synthesis of thyroid
hormones. As their name suggest, they can cause goiter, which is a pronounced swelling in the
neck caused by an enlarged thyroid gland." (p 311)
Soy is not the only goitrogenic food. Broccoli, cabbage, Brussels sprouts, cassava, rapeseed,
turnips, mustard, radish, peanuts and millet also contain goitrogens. However, few adults--and
even fewer children--eat these foods to excess. Furthermore, the goitrogens in most of these
foods are easily neutralized by cooking or fermentation.
Soy foods are different. The principal goitrogens in soybeans are the estrogenic plant hormones
known as isoflavones. The antinutrients known as saponins in soy may also be goitrogens....
Cooking and processing methods using heat, pressure and alkaline solutions will neither deactivate
nor remove isoflavones or saponins. Only solvent extraction can do that. So far, the soy industry
has resisted using these processes--even for soy destined for babies, who are highly vulnerable to
their estrogenic and goitrogenic effects." (pp 311-2)
The causes of so much thyroid disease appear to be many and synergistic. Radiation, mercury,
fluoride, plastics, pesticides, dioxins, solvents and estrogens (and estrogen mimickers) found in
commercial meats, plastics and hormone replacement therapies (HRT) have all been implicated.
And so has soy.
The United Kingdom's Committee on Toxicity (COT) has identified several populations at special
risk for soy-induced thyroid disease--infants on soy formula, vegans who use soy as their principal
meat and dairy replacements, and men and women who are self medicating with soy foods and/or
isoflavone supplements in an attempt to prevent or reverse menopausal symptoms, cancer or high
cholesterol. As early as 1980, British government researchers pointed out that soy-consuming
vegans were at risk." (pp 313-4)
Although iodine deficiency increases the antithyroid effects of goitrogenic foods, iodine sufficiency
does not offer complete protection in the face of high soy consumption." (p 315)
The first report in medical journals of enlarged thyroid glands in rats and chickens fed soybean
rations appeared in the 1930s. In 1961, researchers discovered that spiking the chow with iodine
could prevent goiter. But this quick-fix solution to a serious problem turned out to be simplistic.
Rats and chickens fed soybean-based chows required twice as much iodine to prevent thyroid
enlargement as animals fed soy free diets. Even then, their thyroid glands showed abnormal cell
proliferation. When iodine is largely absent, soy can provoke malignant hyperplastic goiter.
Dr. Mieko Kimura of Kyoto University writes: "It is well known that a goiter is induced by simple
iodine deficiency, but it was noteworthy that hyperplastic goiters can be induced in rats in a high
percentage by the administration of soybean factor(s) under iodine-deficient conditions, together
with accurate signs of malignancy such as invasiveness and metastasis formation in the lungs." (p
315)
Likewise, the soy estrogens known as the isoflavones can inhibit the action of thyroid drugs. to
ensure their efficacy, many health professionals recommend that they not be taken at the same
time as food or supplements high in soy." (p 316)
Boosting the thyroid with drugs like Synthroid, then depressing it with thyroid inhibitors like soy
foods or isoflavone supplements can put extreme stress on the thyroid. Environmental scientist
Mike Fitzpatrick, Ph.D., points out that this is the classic way that researchers induce thyroid tumors
in laboratory animals. The fact that soy is "natural" does not make it safe or weak. A serving of
soy food provides up to three times the goitrogenic potency of the pharmaceutical thyroid-inhibiting
drugs methimazole and 6-propylthiouracil." (p 316)
Mechanisms of action. Plant estrogens interact with the thyroid gland in several ways. Genistein
and daidzein (the key isoflavones in soy) and biochanin A (found in clover and alfalfa) are potent
inhibitors of thyroid peroxidase (TPO), an enzyme involved in the synthesis of T3 and T4. In vitro
experiments have shown that soy isoflavone's inhibition of thyroid peroxidase interferes with a
critical stage in thyroid hormone production--the iodinization of the amino acid tyrosine.
This interference occurs whether or not sufficient or extra iodine is present. As a result, the body
produces useless mono-, di- and tri-iodoisoflavones and not the mono, di, and tri and quarto forms
of thyroid hormone. In the human body, this interference can cause a drop in thyroid hormone
levels, an increase in thyroid stimulating hormone and stress on the thyroid gland." (p 317)
Another way goitrogens damage thyroid function is by increasing concentrations of thyroid binding
globulin (TBG), a plasma protein involved in the inactivation and transport of T3 and T4. This
lowers free thyroxine concentrations and increases TSH secretions." (pp 317-8)
The first reports of thyroid damage suffered by human infants on soy formula appeared during the
1950s. Most cases involved goiter, with no overt signs of hypothyroidism. Although iodine
supplements helped, they did not entirely solve the problem. Researchers found that matters
improved considerably if the processing of the soy formula included extraction with an organic
solvent as well as heating. Although no one at the time identified the principal goitrogens as the
isoflavones, alcohol solvent extraction is, in fact, the only way to remove them. Heat, pressure and
alkaline treatments used in ordinary soy processing will not remove the isoflavones." (p 318)
Autoimmune thyroid disease is far more likely to occur in children who were fed soy formula." (p
318)
The most powerful evidence of soy's adverse effects on the adult thyroid emerged from a study
carried out at the Ishizuki Thyroid Clinic in Japan. Dr. Yoshimochi Ishizuki of Aichi Medical
University demonstrated that 30 grams of pickled soybeans per day, given to healthy adult men
and women, induced thyroid disruptions in only 30 days. All subjects consumed seaweed daily to
ensure adequate iodine intake." (p 320)
Soy eaters are at risk for thyroid damage not only because of the goitrogens in soy but also
because phytates contribute to zinc deficiency and an "anti-vitamin factor" results in greater needs
of the body for vitamin B-12." (pp 322-3)
Soybeans naturally contain goitrogens, allergens, protease inhibitors and other antinutrients and
toxins that damage the digestive, immune and neuroendocrine systems, putting consumers at
increased risk for many health problems, including cancer." (p 381)
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