Soy likes to be criticized. Products from it are said to be harmful. We looked at the study situation and found numerous works, all of which show that soy is very healthy and can have extremely positive effects on osteoporosis, menopausal symptoms, cardiovascular diseases, and some forms of cancer. The main active ingredients in soy are the so-called isoflavones – plant substances with strong antioxidant, anti-inflammatory, and hormone-regulating effects.
How healthy are soy, soy products, and isoflavones?
Soy is always under criticism. Soy products, for example, are said to be harmful because they contain antinutrients such as lectins and phytic acid and would therefore bind minerals so that the body could not absorb them at all. Deficiency symptoms are the result, soy and tofu critics warn.
There are also regular warnings about isoflavones. These are secondary plant substances with very health-promoting properties. However, since they are also counted among the phytoestrogens, i.e. among those plant substances that can have an estrogen-like effect, soy is held responsible for all kinds of hormonal disorders.
Lectins and phytic acid in soy
The lectins and phytic acid, which are often referred to as antinutrients, are contained in large quantities in raw soybeans, but hardly any more in ready-to-eat soy products such as tofu, as an American review from 2014 showed. It resulted in:
- Lectins in soybeans are almost completely destroyed by heat and thus during tofu production (and the production of many other soy products).
- Soaking soybeans in water for 12 hours significantly reduces phytic acid levels. The longer the soybeans are soaked, the lower the phytic acid content. Since soybeans are always soaked and boiled for tofu production, the finished tofu only contains completely irrelevant residues of phytic acid and lectins.
- Fermenting further reduces the phytic acid content in soy products, so fermented tofu contains even less phytic acid.
The researchers came to the conclusion that moderate consumption of soy products in healthy individuals does not lead to any health risks. In addition, more and more studies are showing that the moderate consumption of phytic acid and lectins is to be considered positive for health, as they have been shown to have anti-inflammatory and anti-cancer properties.
The hormone effects of soy: isoflavones in tofu
Another frequent accusation against soy and products made from it relates to their alleged hormonal effect because they contain the plant hormones (isoflavones) mentioned at the beginning. Isoflavones are called phytoestrogens because they have an estrogen-like effect. However, they are much weaker than real estrogen, which is why it is not enough for hormone therapy to simply eat tofu regularly.
Isoflavones are found in numerous plants, but in particularly high concentrations in soybeans. 100 g of raw soybeans contain 128 mg of isoflavones. After processing, only 23 mg of isoflavones can be found in 100 g of firm tofu. For comparison, 100g of peanuts contain just 0.26mg of isoflavones, mung beans 0.19mg, and lentils 0.01mg.
Scientists recommend an amount of 50 to 100 mg of isoflavones per day. With 200 to 400 g of tofu or 150 g of tofu and 250 ml of soy milk (approx. 10 mg isoflavones per 100 ml), one would arrive at a value of approx. 60 mg isoflavones.
Soy and isoflavones in breast cancer
When it comes to soy and breast cancer, there are two contradictory statements: on the one hand, researchers found that isoflavones from soy protect against breast cancer – on the other hand, other studies have also found carcinogenic effects. What is true? In fact, both, as strange as it may sound at first.
It depends on the form in which you take the isoflavones. If isoflavones are taken in isolation as a dietary supplement, the genes that accelerate tumor growth can be stimulated. On the other hand, consuming isoflavones in the form of soy products has an anti-breast cancer effect—particularly in those people who have consumed soy products throughout their lives, ideally since childhood or adolescence.
The isoflavones alone usually do not provide the anti-cancer effect, but only in combination with other substances contained in soy products that influence each other or only in the small amounts that are contained in soy products, while high-dose dietary supplements with isoflavones carry risks recovery That’s why it’s always better for women with breast cancer (or those who want to prevent cancer) to use soy products that are as natural as possible (tofu, soy milk, tempeh) rather than taking supplements with isolated isoflavones.
There are now numerous studies that confirm the positive effect of soy and soy isoflavones on the risk of cancer. And especially in Asia, where soy products have traditionally been eaten for a long time, breast cancer rates are lower than in western countries.
Soy and isoflavones against menopausal symptoms
The consumption of soy is also said to have a positive effect on menopausal symptoms. During menopause, the hormonal balance changes, which leads to typical symptoms such as B. hot flashes. Again, it is the isoflavones that can help here, as studies have shown.
The isoflavone genistein, for example, causes hot flashes to occur less frequently and existing hot flashes to be milder without causing any side effects, as is the case e.g. This can be the case, for example, with conventional medical hormone therapy for menopausal symptoms.
Studies showed that genistein’s protective effect against hot flashes was all the more evident the longer before menopause the subjects regularly consumed soy (e.g. tofu, soy yogurt, or soy milk).
Soy and isoflavones in prostate cancer
But the health effects of soy consumption were not only studied in women. Soy consumption is also said to reduce the risk of prostate cancer, studies show.
The greatest effect was found with tofu compared to other soy products such as miso, natto, and soy milk. People who regularly ate 240g of tofu or more per week had a lower risk of developing prostate cancer than people who ate less than 100g of tofu.
The isoflavones in particular are said to be responsible for this. A detailed article on how soy protects the prostate can be found under the previous link.
There is now also research showing that eating soy (and isoflavones) can reduce the risk of other types of cancer, such as colon, lung, and uterine cancer.
Soy and isoflavones in thyroid disorders
Often one also reads that soy and the isoflavones in it have an unfavorable effect on the thyroid gland and z. B. could cause or exacerbate hypofunction.
However, the studies that indicated that soy might inhibit thyroid function were either laboratory studies with isolated isoflavones or animal studies in which the animals either also received high doses of isoflavones or whose diet consisted largely of soybeans.
Since high doses of isoflavones have nothing to do with the occasional consumption of tofu and people do not live primarily on whole (possibly raw) soybeans, the study results mentioned are not suitable for everyday use.
It is also now known that possible inhibitory effects of isoflavones on the thyroid gland only occur in people who are deficient in iodine, so it makes more sense to keep an eye on iodine levels than to avoid tofu.
Soy lowers cholesterol levels
Cholesterol is mainly found in animal fats and is largely produced by the body itself. As a plant-based food, soy naturally does not provide any cholesterol and, moreover, probably has a cholesterol-lowering effect.
A 2019 review showed that at least soy protein reduced LDL cholesterol (also known as “bad” cholesterol) by an average of 3.2% and total cholesterol by 2.8%. The subjects in the studies consumed an average of 25 g of soy protein per day over a period of several weeks to months. As can be seen in this nutritional table, you can eat 25g of soy protein with just over 150g of tofu per day.
Soy for cardiovascular diseases
High cholesterol is officially considered a risk factor for cardiovascular disease. However, since soy products now have a cholesterol-lowering effect, it is believed that they could also protect the heart in this way – which an American study from 2020 was able to show.
In this study, those participants who ate soy in the form of tofu at least once a week had better cardiovascular health. This protective effect was particularly pronounced in women. A detailed article on the said study (How tofu protects the heart) can be found at the previous link, which also shows that, among other things,
Soy and its effects on the skin
Lately, soy, and tofu, in particular, have even been celebrated for their positive effects on the skin: soy product is said to help against wrinkles, acne, and cellulite. How nice would that be – especially if you already like tofu? But is that the truth?
In fact, there are initial indications of this: animal experiments showed that isoflavones protect against skin aging, and other studies showed that isoflavones from soy also promote wound healing by, among other things, improving skin regeneration. However, research is still in its infancy.
Soy during pregnancy
On soy critic sites, one occasionally reads that one should not eat soy products during pregnancy, as they could lead to malformations in the child due to the alleged hormone effects of isoflavones. They refer to animal experiments that were carried out many decades ago. The animals did not even get tofu, but mostly soy meal or another soybean preparation – and in large quantities at that – so that these results are by no means transferrable.
Instead, more than 1000 studies are published worldwide every year that deal with the influence of soy on health, whereby none of the studies would warn against eating soy products during pregnancy.
On the contrary: Pregnant women are even advised to include tofu in their diet due to its high protein and mineral content.
Can soy be eaten if you have a food intolerance?
Since there are many food intolerances and intolerances today, those affected must always be careful when choosing their food. However, soy products are usually well tolerated. There are two exceptions: If you suffer from a soy allergy or histamine intolerance.
Soy for histamine intolerance
If you suffer from histamine intolerance, you should be careful when consuming soy, as soybeans and products processed from them are among the histamine liberators. This means that they promote the release of endogenous histamine. Fermented soy products such as soy sauces and miso also contain histamine directly and are not suitable for people with a corresponding intolerance.
At most, soy milk and unfermented tofu could be tested in small amounts to see if they are tolerated.
Soy for fructose intolerance
People who suffer from fructose intolerance cannot tolerate fruit sugar (fructose). In the food industry, fructose is often added to confectionery or beverages, but also to dips, dressings, ready-made sauces, etc. However, most soy products, especially naturally unprocessed tofu, do not contain fructose.
Depending on the marinade, if you buy pre-marinated tofu it may contain fructose (albeit in small amounts). Therefore, for marinated tofu or otherwise prepared tofu recipes, you should read the ingredients on the package.
Soy for gluten intolerance
If you suffer from pronounced gluten intolerance (celiac disease), you should always take a look at the ingredients and check whether the food is certified gluten-free. Otherwise, unprocessed products made from soy, such as soy milk and natural tofu, are gluten-free.
However, tofu that has already been marinated may contain gluten, e.g. B. when seasoned with a soy sauce containing wheat or similar (Shoyu). Of course, breaded soy products can also contain gluten.
Soy for lactose intolerance
In the case of lactose intolerance, milk sugar (lactose) is not tolerated. In this case, you can eat soy milk, tofu, and other soy products in general without hesitation. In the case of vegetarian meat substitutes made from soy, however, you should read the list of ingredients, as they may contain lactose. Of course, this is not the case with vegan meat substitutes, since lactose is a food of animal origin.