Problems with Soy Products?
Q&A with Bill Harris, M.D.

Q. I am guessing you know that I am a member of the VegSource family, and author, columnist, etc. I have quoted "Scientific Basis..." in my books and hold your work in high regard.

A. Dear Marie,

Yes, indeed I know about you and appreciate your quote: " According to Dr. William Harris, author of the compellingly persuasive "The Scientific Basis of Vegetarianism" the reply should be "How much [protein] do you think you need"?

I am also considered a soyfoods expert. I have a follow-up question regarding a recent VegSource Q&A regarding a vegan w/high cholesterol. You mentioned undercooked soyfoods as a possible cause of elevated cholesterol. I would love for you to expand on that for me. This is something I have not heard and would be an important topic and one that I should know about.

This was my quote: "Hypothyroidism is associated with elevated cholesterol levels and it in turn can be caused by overconsumption of undercooked soy products."

Then I checked and decided that you had caught me off base. When dinosaurs ruled the Earth and I was a first year med student I thought my biochem prof had said that raw soybeans cause goitre. But now my biochem and nutrition textbooks only mention soy as a trypsin inhibitor but say nothing about goitrogenic properties, although they do put the finger on kale, cabbage, Brussels sprouts, broccoli, rutabaga, strawberries, etc. as goitrogens.

So my immediate thought was "The three signs of old age: the first one is loss of memory and I've forgotten the other two."

Then I went on the web and found some anti-soy gossip that confirms my original position:


... Soy's effect on thyroid was first noticed when hypothyroid babies given soy formula became more severely hypothyroid. They were unable to overcome the anti-thyroid effects of soy. A report to this effect appeared in the New England Journal of Medicine in 1960. Since then many other small studies have confirmed that soy is a goitrogen, a substance that can cause enlarged thyroid (goiter). Soy is listed as a goitrogen in many nutrition books including "Super Nutrition for Menopause" by Ann Louise Gittleman, PhD. Endocrinologists (thyroid specialists) are frequently unaware of the potential anti-thyroid effects of soy on hypothyroid women who are in menopause and are often eating a lot of soy or popping soy isoflavone capsules to ward off hot flashes.

Definition: A substance or product that may cause thyroid enlargement and formation of a goiter, such as soy or millet.

Phytoestrogens Anti-thyroid agents

We're sick of hearing that there are no harmful effects of phytoestrogens. Phytoestrogens disrupt thyroid function.

Theodore Kay of the Kyoto University Faculty of Medicine noted in 1988 that 'thyroid enlargement in rats and humans, especially children and women, fed with soybeans has been known for half a century'.

In fact, thyroid problems associated with soy were also well known to bird-breeders, which is how Soy Online Service first became aware of the goitrogenicity of soy.

Well known, but that fact seemed to escape manufacturers of the first commercially available soy formulas. Those formulas were known to cause in goitre in infants and one can only wonder how many other infants were left hypothyroid or suffering from permanent thyroid damage by soy formulas.

The iodine levels in soy formulas were increased and instances of goitre in infants fed these products ceased. However, there appears to have been no attempt to isolate or remove the goitrogenic properties from soy formulas. This is of grave concern because, although elevated iodine levels would have helped to nullify the effects of the goitrogens, the goitrogens would still have been actively suppressing thyroid function in infants. Hence millions of babies (particularly in the United States where soy formula feeding is most common) have needlessly been exposed to goitrogenic agents; Soy Online Service believe that infants fed soy formulas unnecessarily risk abnormal thyroid function and a greater risk of thyroid disease in later life.

So just what are these goitrogenic agents? In 1997 research from the FDA's National Center for Toxicological Research (NCTR) showed that the darling of the soy industry, the isoflavone genistein, was a potent inhibitor of Thyroid Peroxidase (TPO); in fact genistein is a more powerful inhibitor of TPO than common anti-thyroid drugs! If genistein could inhibit TPO in vitro, it follows that it could result in an elevation of Thyroid Stimulating Hormone (TSH), and a subsequent decrease in thyroxine (T3) in vitro; in other words consumption of the soy isoflavone genistein might result in hypothyroidism and goitre.

Recent research leaves little doubt that dietary isoflavones in soy have a profound effect on thyroid function in humans. A study by Japanese researchers concluded that intake of soy by healthy adults for a long duration caused enlargement of the thyroid and suppressed thyroid function. These researchers studied the effects of feeding 30 g of soybeans per day on thyroid function and found that after one month there was a significant increase in thyroid stimulating hormone (TSH) levels in a group of 20 adults (group I) but no change in thyroxine levels.

Diffuse goitre and hypothyroidism appeared in some of these subjects and about half of another group of 17 adults (group II) that took soybeans for 3 months. This group also had increased TSH levels, especially in older subjects, but once again there was no significant change in plasma thyroxine. After three months of soy intake other relevant symptoms included constipation (in 53% of subjects), fatigue (in 53% of subjects), lethargy (in 41% of subjects). It should be noted that iodine intake (via seaweed) was normal in all subjects.

The goitre was a diffuse goitre (degrees I and II enlargement) and occurred in 3 of group 1 and 8 (47%) of group 2. One subject in group 1 developed sub-acute thyroiditis. Two of the 11 subjects with goitre showed no reduction in goitre size one month after cessation of soy but goitre size was reduced in the other 9 subjects. The two subjects received thyroxine treatment and their goiters reduced in size after two and six months respectively.

The combination of a moderately elevated TSH with a normal free thyroxine defines subclinical hypothyroidism, a condition which may evolve towards overt hypothyroidism especially in persons with anti-thyroid antibodies. The condition is defined as the state in which a reduction in thyroid hormone secretion is compensated for by an increased TSH production to order maintain a clinically euthyroid status. Subclinical hypothyroidism is of increasing importance and its prevalence appears to be growing such that studies to define both its evolution and strategies for its management are warranted. Thyroid experts have noted that dietary factors may well play a major role in the development of this condition since high goitrogen intake can increase TSH secretion.

We have already noted that isoflavones bioaccumulate in infants fed soy formulas. Hence, there is strong evidence from both in vitro and in vivo studies that persistent TPO inhibition will occur in infants subjected to soy formulas long-term (for more than three months). The work of Ishizuki indicates that this persistent exposure to the anti-thyroid agents in soy will result in variable and elevated levels of TSH, even if iodine levels are sufficient. There is a bounty of evidence showing that scenarios such as this can result in various thyroid diseases in humans.

Soy Online Service believe that it is utterly irresponsible for soy formula manufacturers to continue to place infants at risk of thyroid damage by refusing to remove isoflavones from their products. Soy Online Service also believe that it is totally irresponsible and a sign of moral corruptness to promote anti-cancer benefits of soy without any inference that there may be other health risks (for example to the thyroid).

There is an epidemic of thyroid disease in the United States. If you were fed a soy formula and suffer from a thyroid disorder, or have any reason to believe that soy may have caused you to develop a thyroid disorder, please contact us.

More information on developmental disorders caused by thyroid dysfunction is available here.


Useful advice for sufferers of thyroid abnormalities is at Krispin Sullivan's website

For more information on thyroid disease, visit Mary Shoman's thyroid website and also read the following article by Robert J. Thiel published on Also read Jennifer Phillips article on Thyroid Hormone Disorders.

"From 'Hippocrates Health' the popular Australian health resource website:

Read the testimonies of people who have suffered thyroid problems because of soy/isoflavone supplements and the shocking results of Larrian Gillespie's "self as a guinea-pig" experiment.

Also read our Big Ugly Bull Award to the FDA-CFSAN for endorsing the consumption of thyroid disease causing compounds. Introduction

Spreading the truth about soy.

Soy Online Service is a small group of private citizens with a mission to inform the public of the truth about soy. We have no membership as such and are not sponsored by industry or any other group, in fact our research is funded out of our own pockets. We do not seek the destruction of the soy industry or to stop people eating soy. We have no desire to stop you being Vegan or to cause you to switch to dairy products. Rather we seek to expose the deceit of the major soy companies and to uncover the truth about soy products. We do this by providing you with factual material that you can read for yourself, so that in the future you can make an informed choice about what you eat.

You are probably well acquainted with all the wonderful things soy is purported to do for you. That's because the multi-million dollar soy marketing machine has done its job on you. But are you aware that there is a darker side of soy?

For instance did you know that soy contains several types of natural toxins? The soy industry has known about them for years. If you were to ask the soy industry about the soy toxins you'd most likely be told that: (blah, blah, de blah...........)


Most of the nearly slanderous remarks above strongly smell of cow's with black Fedoras carrying violin cases, so I would like to know who really put this stuff out. However, I don't know of anyone who eats uncooked soy and see no reason to avoid tofu and other soy products in moderation. Being vegan isn't just about eating soy beans though, and there are plenty of other good plant protein sources.

Basically, I wanted the gentleman who asked about his high cholesterol and his thyroid problem to know that there could be a theoretical connection if he was one of the few who tries to eat raw soy products. It's not very likely though. Sincerely,

-Bill Harris, M.D.