Key points:

Soy is a complete protein - contains all nine essential amino acids
It has many health benefits including lowering cholesterol
Good for bone and muscular health
Hard to digest, fermenting is recommended
All highly processed versions of soy are bad for your health
Soy contains many plant toxins, some of which mimic oestrogen (phytoestrogens)
Phytoestrogens can disrupt hormonal balance, but may also have many health benefits
Studies looked for a correlation between soy consumption and decrease in sex hormones in men
Difference between soybeans and edamame beans
Fermented soy foods
Chemically produced soy sauce contains many harmful ingredients

Not many plant foods provide all nine essential amino acids (EAAs). The ones that don’t have to be combined with others to provide you with your daily need of EAAs (kidney beans and rice, for example). Here are the ones that do contain all nine EAAs: quinoa, buckwheat, hemp, chia seeds, spirulina, tempeh, amaranth, and soy.

Soy is good for you

Soy is a legume that is often considered a good alternative to meat. It is a food very rich in protein and a great source of vitamin C, calcium, iron and folic acid. It is also relatively low in carbohydrates but high in fibre.

The high-fibre content and other compounds in soybean products and edamame beans may contribute to lowering LDL cholesterol and triglycerides while raising HDL cholesterol, all important for the health of your cardiovascular system. Fibre can reduce the absorption of circulating cholesterol into your bloodstream.

Isoflavones are the ‘notorious’ phytochemicals in soy (phyto- meaning plant) that have gotten a mixed reputation over the last years. They may help reduce blood pressure and improve arterial health (more on isoflavones later).

Soybean is one of few foods that provide ample amounts of both omega-6 and omega-3 fatty acids, both important for the healthy functioning of the cells and brain while providing a good ratio of pro- and anti-inflammatory effects respectively.

Soybeans and edamame beans are plant-based superstars in their content of important minerals needed for the health of your bones and skeletal structure. Calcium is usually at the forefront of this, but these legumes also contain a decent amount of copper, iron, magnesium, phosphorus, potassium, and zinc.

But the protein in soy is not easy to break down and is very tough to digest. Cultures that traditionally use a lot of soy in their cuisine tend to ferment the beans to preserve them better, and this also helps with digestion and reduces the antinutrient content. Just like when cabbage turns into sauerkraut the bacteria involved in fermentation pre-digest the food. This bacteria population is very beneficial for us as they are a part of our normal gut flora.

Soy is bad for you

Despite the fact that soy has been a staple in Eastern cuisine for centuries, it has gotten a lot of bad publicity over the past years mainly due to its phytochemical compounds.

However, the major problem with soy consumption in western cultures is that soy is mainly consumed in highly processed forms like soybean oil or soy lecithin (a combination of soybean oil and phospholipids used as an emulsifier in food products). We have discussed the toxicity of soybean oil in our article on vegetable oils. Soy lecithin can trigger allergies in people sensitive to soy and even disrupt cognitive function and brain chemistry.

We also get soy in protein bars and powders where it comes in the form of soy protein isolate. This process requires various chemicals to extract protein from it which again makes it a chemical product, a foreign substance to the body. You can also find textured vegetable protein on the supermarket shelves which is again an altered soy protein, often accompanied by caramel colour and other additives.

Above all, virtually all soy on the market is genetically modified. Look carefully for the organic label when purchasing.

There is some research that links soy to digestive and reproductive issues and cognitive decline, however many other studies couldn’t find a correlation. Soy is high in so-called antinutrients, particularly isoflavones. Antinutrients are defence mechanisms within a plant that can inhibit the absorption of vitamins and minerals and can cause all kinds of gastrointestinal and inflammatory issues if toxins accumulate to high levels. See our article on antinutrients.

Oestrogen mimicking compounds

Isoflavones found in soy are compounds similar to estradiol, the main form oestrogen takes in the human body (they are called phytoestrogens, again phyto meaning plant). Since they fit into the same receptor sites in the human body they can sometimes act just like oestrogen and at other times they can actually block oestrogenic effects. This may change the body’s hormonal balance, and sometimes disrupt the reproductive cycle and thyroid function.

However, these plant oestrogens are about 1,000 times less potent than oestrogen in our bodies and can actually help reduce some of the unwanted effects of oestrogen. While they do bind to the same receptors, isoflavones can’t for example stimulate vaginal maturation while oestrogen can. Oestrogen is an important hormone with unique properties and numerous functions in the body.

There is intriguing animal and epidemiologic evidence indicating that modest amounts of soy consumed during childhood and/or adolescence reduce breast cancer risk. Soy consumption can help alleviate hot flashes and reduce symptoms of menopause, including decreases in bone density that can lead to osteoporosis. Some evidence suggests that it reduces prostate cancer risk and inhibits prostate tumour metastasis, but additional clinical research is needed.

Several studies and case reports describing feminizing effects including lowering testosterone levels and raising estrogen levels in men have been published. For this reason, a 2010 meta-analysis compared testosterone and other sex hormones in over 2,500 men to see if any conclusions could be drawn. They found that regardless of dose and study duration, neither soy protein nor isoflavone exposure affects sex hormone levels in men.

Other foods containing phytoestrogens

Phytoestrogens are found in many of the healthiest plant foods and recent studies show that foods that are highest in phytoestrogens tend to also be good for heart health and brain health, help to fight obesity and cancer, and promote longevity.

Along with soy, other legumes like garbanzos and green beans contain plenty of phytoestrogens. Other examples are sprouted plants including alfalfa, clover, and mung bean sprouts. Nuts and seeds like pistachios, chestnuts, walnuts, hazelnuts, and cashews are also good examples while whole grains like oats, wheat, barley, and rice, don’t lag behind either. Then garlic and onion too, and last but not least many leafy greens, cruciferous vegetables and fruits such as blueberries, peaches, strawberries, and raspberries.

Factors that affect isoflavone consumption

Fermentation alters the chemical makeup of soy, which can significantly reduce the level of isoflavones. Prolonged cooking, simmering, or soaking can also reduce phytoestrogen content. Steaming causes less phytoestrogen loss than boiling or frying.

And not to forget we are all different. Your gut microbiota plays a key role in the bioactivity and bioavailability of phytoestrogens, as they are the entities that decide what to turn phytoestrogens into.

Should you still be concerned about the amount of isoflavone consumption?

As shown, phytoestrogens like isoflavones in soy can be a part of a healthy balanced diet for most people. However, there is not enough data yet on the cumulative effect of all the phytoestrogens a person has eaten over their lifetime, and how early these foods were introduced. There is especially a concern with processed soy products.

People with the rare lung disease LAM may especially want to limit phytoestrogens, since the LAM cells have estrogen receptors on them, and may proliferate in the presence of high levels of the hormone and potentially of estrogen mimickers, as well.

Also, (largely theoretical) studies suggest that people with iodine deficiency with hypothyroidism should avoid isoflavone consumption. While the impact of phytoestrogens may vary based on the person’s age, soy isoflavones, in particular, may negatively affect thyroid function in people with hypothyroidism in the absence of sufficient iodine.

Examples of healthy soy products

Let’s stop at edamame beans first. The difference between edamame and soybeans is that edamame beans are harvested when they are young and served fresh, often steamed while still encased in their pod. You eat them shelled. The tender green soft seeds make a nutritious snack or main vegetable.

Soybeans that are left to ripen turn into hard dry beans, which are typically yellow but can be black or brown. Mature soybeans cannot be eaten raw and must be cooked or fermented.

Tofu is made from condensed soy ‘milk’ while tempeh is made from fermented soybeans. Tempeh packs double the amount of protein per serving compared to tofu and four times the amount of fibre while also supplying your gut with healthy bacteria. Tempeh is also a good source of prebiotics which are natural, non-digestible fibres that promote the growth of healthy bacteria in your digestive tract.

Miso is a Japanese traditional paste produced by fermenting soybean with the fungus Aspergillus oryzae and salt, and sometimes with rice, wheat, or oats. Another traditional Japanese soyfood natto is produced by fermentation using a strain of Bacillus subtilis, it is an extremely rich source of vitamin K2.

All these fermented products are highly beneficial for your gut health while being a good source of plant-based protein containing all the amino acids needed for muscle synthesis.

Soy sauce

Traditionally made soy sauce is produced by soaking soybeans in water and roasting and crushing the wheat, then mixing them together with a culturing mould and leaving for a few days to develop. When water and salt are added, the entire mixture is left in a fermenting tank for five to eight months.

High-quality soy sauce uses only natural fermentation. These varieties are often labelled “naturally brewed.” The ingredients list will usually only contain water, wheat, soy and salt.

The quicker and less expensive method uses chemicals and can produce the sauce in a few days. In this method, soybeans are heated to 176°F (80°C) and mixed with hydrochloric acid. Unfortunately, many substances produced during traditional fermentation are missing, therefore, extra colour, flavour and salt are added. The label on this type of soy sauce will usually list hydrolyzed soy protein or hydrolyzed vegetable protein as ingredients.

The usual concerns with soy sauce are the high levels of sodium (one tablespoon contains around 900 mg or 38% of RDI) which can be healthy in moderate amounts, but dangerous for people with already raised blood pressure.

Yet a more concerning factor is that chemically produced soy sauce can be high in cancer-causing compounds like chloropropanol (3-MCPD). Soy sauce also contains high amounts of amines, especially histamine and tyramine which can have toxic effects in high quantities.

Because chemically produced soy sauce lacks fermentation, monosodium glutamate (MSG), a flavour enhancer, is added to provide the missing umami flavour. Symptoms such as headaches, numbness, weakness and heart palpitations are sometimes linked to the consumption of MSG.

Lastly, soy sauce is also a source of wheat and gluten, so sensitive individuals should look for gluten-free soy sauce.

Overall, like most foods, soy sauce can be enjoyed in moderation as part of a healthy diet, especially if naturally fermented soy sauce can be obtained.

Conclusion

I admit, that I went into the research for this article a bit biased trying to write about the negative effects of soy consumption, especially the oestrogen-mimicking compounds. But I couldn’t find any conclusive research to support my theory, in fact, I found more evidence to support the opposite!

However, I would still prefer to alternate soy with other good-quality plant-based sources of protein rather than having it as a staple.

So, in conclusion, soy can definitely be healthy food if it’s a part of a balanced diet. Always look for organic soy products that are lightly processed like tofu, or even better, opt for edamame beans as they are in their most natural form. Even better yet, go for fermented soy like tempeh, miso and natto and combine them with plenty of other fresh vegetables. Always check the ingredients label on the packaged products and avoid all soy-based additives if possible.

If your concern is the consumption of plant toxins think of it this way - in moderate amounts they will most likely increase your resilience to many diseases as this is a form of light stress for the body. A bit of stress is what makes us stronger. Just like too much stress, no stress is what makes us weaker and more vulnerable.

Stay in tune with your body and it will tell you what works and what doesn’t.

Resources:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5188409/

https://foodrevolution.org/blog

https://www.youtube.com/watch?v=ZtWjQna2cUM

https://pubmed.ncbi.nlm.nih.gov/20980639/

https://www.livestrong.com/article/447704-differences-between-soy-beans-edemame/

https://www.livestrong.com/article/13726919-edamame-nutrition/