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Soy And The Thyroid

Soy products provide variety on the menu. However, like hardly any other food, soybean has to be criticized, if not discredited. So she should u. contain the dangerous-sounding goitrogens and are therefore not good for the thyroid. Goitrogens are substances that can affect thyroid function. However, it has been known for a number of years that soy products – if you pay attention to two small things that are actually taken for granted – cannot harm the thyroid gland.

Soy and the Goitrogens

Soy products are extremely versatile because almost anything can be made from soybeans: soy milk, soy cream, soy ice cream, soy burgers, minced soy meat, soy schnitzel, soy sausages, and much more. Nevertheless, soy products by no means only have friends. On the contrary, there is a critical article on every corner of the Internet. Significantly, it is always the same that circulates through the Internet – with always the same sometimes ancient, sometimes questionable sources.

For example, soybeans are accused of containing so-called goitrogens or having a goitrogenic effect. Literally translated, “goitrogen” means “goitrous”. Soy products are said to have a negative effect on the thyroid gland and lead to an under the function of the same, yes, they are even said to be able to cause thyroid cancer.

Soy – only problematic if consumed in excess

In the anti-soy book by Kaayla T. Daniel (Soy – The Whole Truth), you will find several testimonials from people who had consumed soy products and allegedly developed thyroid problems after a few weeks or months. None of these individuals consumed normal amounts of soy products. In every field report, on the other hand, you will find passages like this:

“…So I ate tofu daily, drank decent amounts of soy milk, nibbled soy nuts instead of regular snacks, and made sure my supplements contained isoflavones.”
Or “…In the past year, I’ve eaten tons of tofu, edamame, soy meat substitutes, soy cheese, soy butter, soy sour cream, soy cream cheese, soy yogurt, and especially soy milk – preferably with a chocolate flavor. In the past three to six months I’ve had three to six Cups (= 750 to 1500 ml) of soy milk drunk daily…”
A 17-year-old also has her say, who was diagnosed with thyroid cancer at that young age. She reports that she was not breastfed as a baby but was fed soy formula. She also writes that she drank several bottles of soy sauce a week as a child (not soy milk!) – and did so for years (“Yes, I was a strange child,” says her report). In addition, she was a vegetarian before she reached puberty, which is why soy products made up a large part of her diet because she wanted to give her body enough protein.
What is clear from all these reports? These people are extreme exceptions. They were consuming absolutely abnormal amounts of soy products.

Also, how many youths are there who have cancer and have NOT eaten soy? And conversely, how many children, adolescents and adults are there who eat soy products (in normal amounts!) and are healthy? So it doesn’t help the cause to list individual cases that eat so strangely that their experiences can’t be extrapolated to normal people – unless you’re also prone to excessive soy binge eating.

Substances in soybeans with goitrogenic effects: isoflavones

The goitrogenic substances in soybeans are none other than isoflavones, i.e. those secondary plant substances that are praised elsewhere for the positive health effects of soybeans.

Incidentally, isoflavones belong to the large group of flavonoids. Surely you have already heard of these substances – and probably only the very best. Because flavonoids are those plant compounds that are considered great antioxidants, detoxifiers, cancer fighters, and anti-inflammatories.

Apart from the isoflavones of the soybean, the flavonoids also include the anthocyanins (blue, violet, and dark red plant pigments in berries, flowers, aubergines, etc.) and the famous epigallocatechin gallate (EGCG) in green tea. The latter is u. a. Used to prevent cancer, support detoxification, and inhibit Alzheimer’s and Parkinson’s disease.

And now exactly these substances are suddenly harmful? Yes, they are – if you take the substances in the isolated and highly concentrated form daily and permanently. Because that’s not what these fabrics are made for.

Therefore, there are also studies on EGCG that show that this substance, which is actually so healthy, can inhibit thyroid function. However, does drinking a cup or two of green tea a day inhibit thyroid function? Does it inhibit them if you take a course of green tea extract for detoxification? no EGCG inhibits the thyroid function if you take this substance permanently, isolated and highly concentrated or if you drink green tea or matcha in excess.

Exactly the same applies to the isoflavones of soybeans and thus also to soy products. Anyone who uses isoflavones e.g. B. in capsule form in high doses as a dietary supplement or eats a lot of soy products runs the risk – with the appropriate predisposition – of developing thyroid problems.

The thyroid study of the soy opponents

Since soy only has an unfavorable effect in certain cases and with certain consumption habits, it is no wonder that anti-soy sites can usually only cite a single human study as proof that soy is allegedly harmful to the thyroid gland. This dates from 1991, so it’s not exactly up-to-date anymore and it’s only available in Japanese. Only the tables of measured values ​​and the abstract (the summary) can be viewed: It describes that 37 people were divided into three groups:

  • Group 1 (20 participants) ate 30 g of pickled soybeans daily for one month.
  • Group 2 consisted of 7 younger subjects in their 30s who ate the soybeans for three months.
  • Group 3 (10 participants) also took the soybeans for three months but consisted of older people (around 60).

The result:

In all groups, the different serum levels of thyroid hormones remained unchanged even after soy consumption, but TSH levels increased but remained within the normal range.”

Do soy products harm the thyroid?

TSH is the control hormone released by the brain (the pituitary gland) when it thinks the body needs more thyroid hormone, e.g. B. is the case when the person does sports or when he suddenly gets cold. Because the metabolism always has to be activated – and the activation of the metabolism is the main task of the thyroid hormones.

Permanently elevated TSH values ​​can therefore indicate hypothyroidism since the TSH level would drop immediately if sufficient thyroid hormones were formed. Only when the thyroid gland cannot respond to the TSH signal does the TSH remain chronically elevated.

However, the officially applicable standard values ​​for TSH are often set from very low to very high, so that even TSH values ​​that are in the upper part of the standard values ​​lead to symptoms of hypofunction in a number of patients, but at the same time are still considered completely normal by quite a few doctors will.

So could hypothyroidism occur after just a few weeks on just 30g of soybeans a day? Not only that: but according to the Japanese researchers, half of the subjects in groups two and three also developed goiters.

Soy consumption and hypothyroidism: no connection

The number of subjects in the Japanese study was very small. Studies with this small number of participants are usually not considered representative.

Pickled soybeans in the quantities described are also a very traditional and classic part of Japanese cuisine. All of Japan – where between 25 and 100 mg of isoflavones are consumed per day (see list below) – would have to suffer from an underactive thyroid with goiter, which is not the case.

On the contrary. A 2009 study found that of the 1,818 Japanese adults studied, only 12 had symptomatic hypothyroidism and only two of those 12 had a palpable goiter.

For a better overview, here is a selection of soy products with the corresponding isoflavone content.

  • 100 g of tofu provides about 25 mg of isoflavones.
  • 100 g soy drink provides 7 – 9 mg isoflavones.
  • 100 g tempeh provides 43 mg isoflavones.
  • 100 g of soy provides 1.6 mg of isoflavones.

Germany: Little soy – many thyroid problems

Researchers from the University of Wurzburg examined the situation in Germany in 2004 and, in an examination of 96,000 randomly selected employees from various companies (aged between 18 and 65), discovered that around 33 percent had a goiter and/or thyroid nodules. Thyroid disorders are therefore widespread in Germany, the scientists wrote in the journal Thyroid.

However, it is completely impossible that a third of the population consumed soy products every day and therefore developed goiters – especially since a study from 2002 showed that soy products are consumed very little in Europe (less than 1 g per capita and day) so that the high number of thyroid diseases must clearly have other causes.

Further studies show a connection to iodine intake, for example – at least in Japan. The more iodine people take in there, the higher the risk of developing a marked hypofunction.

A vegan diet protects well against thyroid disorders

A 2013 study looked at how different diets affect the thyroid. A normal diet (with meat, fish, etc.) and a vegetarian diet (with eggs and dairy products) were found to be associated with a higher risk of hypothyroidism, while a vegan diet appeared to be more protective of hypothyroidism.

This surprised the researchers, as one would actually have expected the opposite. Because vegans in particular eat soy products, consume a lot of vegetables (and cabbage is also considered goitrogenic like soy), and also consistently avoid fish and seafood, which is why some “experts” always fear that vegans would suffer from an iodine deficiency.

Once again it showed

  • that a well-planned vegan diet is well supplied with all nutrients and vital substances, including iodine,
  • that soy products have no harmful effect on the thyroid gland and
  • that a vegan diet provides additional protective substances that can successfully ward off diseases or organ dysfunctions such as those of the thyroid gland.

Studies: Soy is not the cause of thyroid disorders

The current data confirm the assumption that soy products are not among the main causes of thyroid disorders. A great many scientists and universities have devoted themselves to this topic in recent years – and it is hard to believe that they were all paid for and bought by the “evil” soy industry, as is often claimed.

On the other hand, one would have to assume that all anti-soy studies are sponsored by the meat industry. And indeed: The aforementioned anti-soy article most likely comes from members of the Weston A. Price Foundation, an organization whose statutes the promotion of milk consumption and the consumption of plenty of animal fats is an important point. Kaayla T. Daniel – author of the 500+ page anti-soy book mentioned above – is also a member of the Board of Directors of the Weston A. Price Foundation. But now to the study results of the last ten years:

No change in thyroid levels from soy consumption

In 2006 there is a review that was published in the journal Thyroid. The research team in question had analyzed all human studies available at the time (14 pieces) in which the connection between the thyroid gland and soy was mentioned somewhere and at least one thyroid value was determined.

With one exception, these studies found either no changes in thyroid levels as a result of soy consumption, or very little. The result was that interaction could only occur if synthetic thyroid hormones were taken as medication. Then, in some (!) cases, soy products can inhibit the absorption of the hormones, but this can be compensated for with a slightly higher dose of hormones.

Incidentally, soy is not alone in this effect. There are many other foods and dietary supplements that should not be taken together with thyroid hormones (fiber, calcium supplements, some herbs, zeolite, etc.), but they are by no means unhealthy. Dairy products should also not be taken with thyroid hormones, as we explained here: Dairy products inhibit thyroid hormones.

According to the researchers at Loma Linda University in California, it is therefore not necessary for people with thyroid problems to avoid soy products, especially since the thyroid hormones are usually taken on an empty stomach (and not together with a soy meal) and – if necessary – the dose of the hormones can be increased can adjust at any time.

However, a simultaneous iodine deficiency in combination with soy consumption can increase the risk of hypofunction. This is because isoflavones are thought to bind to the iodine that is supposed to bind to the amino acid tyrosine to make thyroid hormone. For this reason, among other things, isoflavones are considered inhibitors of thyroid hormone formation. However, studies have shown that iodine binding to isoflavones is negligible and not clinically relevant.

As a precaution, however – as is advised elsewhere – one should ensure a good supply of iodine. But an adequate iodine supply (not too much and not too little) is of course always important – whether you eat soy products or not.

Years of soy: No thyroid effects

In 2010, the results of a three-year randomized, double-blind, placebo-controlled study in postmenopausal women were published. They had taken 54 mg of soy isoflavones (genistein) daily for three years – which was more than the 30 g of pickled soybeans in the Japanese study mentioned above. Despite this long period of taking the isolated substances, there were no changes in the thyroid values ​​(not even in the area of ​​antibodies) and no signs of hypothyroidism.

Five years later, another three-year study was published (in Menopause magazine). Again, women received soy isoflavones. Group 1 was the placebo group, Group 2 received 80 mg of isoflavones per day and Group 3 received 120 mg per day. There were no side effects in terms of thyroid function in any group.

Soy protein isolate: No change in thyroid levels

In 2015, a study by researchers from the University of Freiburg was published in the journal Experimental and Clinical Endocrinology & Diabetes. In this study, 14 normal-weight and thyroid-healthy women were given a soy protein isolate-based weight loss shake for 8 weeks. The shake was 44 percent soy protein. The women should start with 25 g of the shake powder per day and increase the dose by 25 g weekly until they reach 125 g. The isoflavone content was 1.45 mg per gram of powder.

The isoflavone levels in the blood (genistein, daidzein, glycitein, equol, etc.), the thyroid levels (TSH, fT3, fT4), and the sex hormones (estrogen, progesterone, testosterone, and DHEA) were checked weekly.

The isoflavone levels in the blood increased significantly, even after consuming 25 g of the powder – which is of course positive, as it shows that phytochemicals are not simply excreted with the stool, but enter the bloodstream and produce those helpful effects there. what is promised from them? In the present study, the thyroid values ​​remained within the normal range, as did the sex hormones, even when 55 g of pure soy protein isolate was eaten daily (125 g of the powder).

Soy during pregnancy

Another soy study followed in June 2016, again with women as test subjects. They suffered from the so-called gestational diabetes. One group of women ate a high-fiber, high-carbohydrate diet, while the second group substituted 25 percent of the carbohydrates with soy protein.

After just one week, it was found that the women in the soy group hardly needed any more insulin therapy, an effect that lasted until delivery. In addition, no noticeable change in the thyroid values ​​was detected, neither in the values ​​of the mothers nor later in those of the infants.

A current summary of all soy studies

In November 2016, the open-access journal Nutrients published a summary of all the data available to date on soybeans and their health effects. It includes reading:

  • The suspicion that soy could impair thyroid function originally arose from in vitro studies and animal studies using isolated isoflavones.
  • A few decades ago, thyroid problems still occurred in children who used soy-based infant formula. However, this problem could be solved as early as the mid-1960s by fortifying infant formula with iodine. Only children with congenital hypothyroidism should not be given soy infant formula.
  • However, population studies and clinical studies in adults show that soy products provide health benefits at two to four servings per day and that soy products can be used as a substitute for less healthy foods. In this way, soy products can help reduce the risk of chronic diseases.”

The healthy consumption of soy

We summarize what to look out for when consuming soy:

  • You should NOT feed your baby soy formula. Nor would they feed an infant exclusively on cheese, lentils, meat, or orange juice. An infant needs the mother’s milk, not a bean!
  • Anyone who eats a vegetarian diet and believes that they have to eat a LOT of soy to be able to cover their protein requirements is on the wrong track and is NOT eating healthily! There are many other plant-based protein sources that provide protein. By the way, TOO MUCH protein is not good either – no matter what source it comes from.
  • One should not live from soy products alone and therefore not consume “huge amounts” of them. Neither should one eat bananas alone, lettuce alone, cheese alone, or pie alone. Soy products are not a single food – neither for babies nor for adults – but food that, in moderate amounts, can complement a healthy diet.
  • You shouldn’t drink soy milk by the gallon or eat soy yogurt by the gallon.
    In our opinion, one should not take supplements made from isolated isoflavones or soy protein isolates, even if these did not show any harmful side effects in the studies mentioned above.
  • But the consumption of z. B. daily 60 – 150 g tofu and glass (150 – 180 ml) soy milk is from our point of view harmless, even health-promoting. However, daily consumption of soy milk is of course not necessary in a vegan diet, since there are other types of plant-based milk, e.g. B. oat or almond or rice milk, which can enrich the daily menu accordingly.
  • If you do not tolerate or do not like soy products, you should of course not eat them! However, this applies to every food – also for grain products, dairy products, fruit, garlic, coffee, etc. You always observe yourself and your own well-being and choose the foods that are personally best tolerated.
  • It should be remembered that the majority of people never eat soy but suffer from serious chronic diseases, while there are countless people who eat soy and are in excellent health. There are also many people who switched their diet to a plant-based diet containing soy and were only able to overcome their symptoms in the first place.
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Written by Micah Stanley

Hi, I'm Micah. I am a creative Expert Freelance Dietitian Nutritionist with years of experience in counseling, recipe creation, nutrition, and content writing, product development.

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