31 Mar 2023 Article

Is soy healthy or not? If you ask the scientists, it is simple: soy in food form is healthy and there is no need to be afraid of it.

But consumers often think differently. Soy is elevated to a super food by some, with claims of taming hot flashes, warding off osteoporosis, and protecting against breast and prostate cancer. At the same time, soy is shunned by others for fear of causing breast cancer, thyroid problems and dementia, although these claims are not scientifically substantiated. The confusion often has to do with the phytoestrogen that soy contains.

Phytoestrogen in soy

Estrogen is the main female hormone. Soy is a food that is widely studied for its estrogenic and anti-estrogenic effects on the body. Yes, that’s right, estrogenic AND anti-estrogenic effects. How is that possible?

Soy contains a high concentration of isoflavones. Isoflavones are a type of plant estrogen (also called phytoestrogen). It is similar to human estrogen, but with much weaker effects. Soy isoflavones can bind to estrogen receptors in the human body and, as a result, can affect the amount of estrogen released by your body. They can increase it or, conversely, decrease it. Soy isoflavones therefore seem to cause different reactions in your body. How exactly?

The exact effect of soy isoflavones has to do with the concentration of female hormones. Pre-menopausal women have much higher levels of estradiol – the main form of estrogen in the human body – than post-menopausal women. In pre-menopausal women, soy may act as an anti-estrogen. But in post-menopausal women, soy may actually act more like an estrogen. Phytoestrogen, as it were, optimizes the existing hormone levels.

Studies show that a lifelong diet rich in soy products reduces the risk of breast cancer in women. So, eating soy foods does not increase the risk of breast cancer or other cancers. Foods made from soy do not contain enough isoflavones to increase the risk of breast cancer. Isoflavone supplements, on the other hand, contain much higher amounts of isoflavones than natural foods (see table below). Some studies have suggested a link between isoflavone supplements and an increased risk of breast cancer in women with a family or personal history of breast cancer or thyroid problems. So do not take isoflavones on your own initiative. Consult your doctor or dietician first.

And no, men don’t get breasts from eating tofu and their testosterone levels don’t go down.

Nutritional value of soy

Aside from their isoflavone content, soy products are rich in other nutrients, including B vitamins, potassium, magnesium and high-quality protein. Unlike some plant-based proteins, soy protein is considered a complete protein, containing all nine essential amino acids in high amounts. That is why soy is the primary source of quality protein for strict vegetarians/vegans.

And did you know that soy drink is the best alternative to cow’s milk? Other types of vegetable “milk” such as oat, almond or rice drink lack high-quality proteins. But soy drink contains as many as cow’s milk.

Soy products are classified as fermented or unfermented. Fermented means that the soy food has been cultured with beneficial bacteria such as yeast or mold. It’s probably true that fermenting soy improves the digestibility and absorption of soy in the body because fermenting already partially breaks down the sugar and protein molecules in soy.

Especially for you, I have made an overview table with the amounts of isoflavones and proteins in different soy products.

Product type Isoflavone content (mg) Protein content (g)
Soy milk, one cup, about 225 ml  6 7
Soy burger, 1 serving  6-7 12-16
Tofu, 100 g  20 8-14
Tempeh, 100 g  30 13
Dried soybeans, cooked,
½ cup, about 100 g
 55 14
Soy Isoflavones, 1 capsule  100-750 0

How much soy can you eat?

Scientific evidence shows that regular consumption of 2-4 servings of soy products per day is not only safe, but also beneficial to health. One serving is one glass (225 ml) of soy milk or 100 g of tofu, tempeh or cooked soybeans.

The Nutrition Center of the Netherlands makes a special recommendation for pregnant women. They are advised not to take too many soy products. This is because of the isoflavones. If you ingest high doses of this during pregnancy, it may affect the development of the baby’s genitals. Convincing evidence is lacking. But this advice is given as a precaution.

But how much is not too much? The Nutrition Center advises (during pregnancy) not to eat or drink more than four glasses (150 ml) of soy drink/yoghurt per day. And also use other soy products, such as tofu, tempeh or soybeans, no more than twice a week. So, you are still “allowed” to eat quite a lot of soy products.

What about GMO in soy?

Soy can be genetically modified. This is then stated on the label, this is mandatory. Genetically modified soy is mainly grown in the United States and South American countries and is mainly used as animal feed. You will NOT find genetically modified soy in European supermarkets.

A few inspirational recipes using soy

Do you want to eat soy products more often but don’t know what you can make? Here are three delicious recipes for you:

Vegan spring rolls

Tofu stir fry

Vegan broccoli patties

Silken tofu mousse

Enjoy your meal!