Is soy healthy or harmful?
Depending on who you speak to, soy is either one of the healthiest foods on the planet or a hormone disrupting toxin that should be avoided at all costs. Over the years I've had people try to convince me of both.
Soy is also a food that everyone has an opinion on. These days for every tofu fanatic there is an avid soy dodger who refuses to even look twice at a bottle of tamari. So which one should we listen to?
Can soy be part of a healthy diet, or is it better to be avoided entirely?
Let's take a look at the evidence.
What is soy?
Soybeans are a legume native to East Asia. However, due to modern demand and the cheap cost of production, soybeans are now grown more or less all over the planet.
Traditional forms of soy such as tofu, tempeh, miso and natto have been a consistent part of traditional Asian diets for thousands of years. These foods are still widely consumed across the entire continent, and are a key component in the diets of some of the world’s healthiest populations (including the blue zone of Okinawa, Japan.)
Nutritionally speaking, soybeans are a pretty impressive food. They are a great source of protein and contain a complete amino acid profile. They are also a good source of calcium, zinc, iron, magnesium, folate, riboflavin (B1) and thiamin (B2).
| Nutrition facts: Soybeans, cooked (boiled) - 100 grams | Amount |
| Calories | 141 |
| Protein | 12.3g |
| Carbohydrate | 11.1g |
| Sugars | 3g |
| Fat | 6.4g |
| Fibre | 4.2g |
| Riboflavin | 0.2mg (9% DV) |
| Thiamin | 0.3mg (17% DV) |
| Folate | 111mcg (28% DV) |
| Calcium | 145mg (14% DV) |
| Iron | 2.4mg (14% DV) |
| Zinc | 0.9mg (6% DV) |
| Magnesium | 60mg (15% DV) |
Fermented soy foods such as tempeh, miso and natto also contain probiotics which are essential for digestive health, along with vitamin K2 which is beneficial for bone and heart health.
Fermented soy has also been shown to have a higher mineral concentration than regular soybeans. This is because the fermentation process converts the minerals into more soluble forms, making them easier for the body to absorb.¹
One of the most significant benefits of soy consumption is that it has been shown to reduce the risk of two of the most common cancers: breast cancer in women², and prostate cancer in men³.
This is largely thanks to a compound in soy known as isoflavones or phytoestrogens (more on these later), which inhibit cancer cell invasion in breast and prostate tissues.
Another important benefit of soy is its positive impact on bone health. The isoflavones in soy have been shown to significantly improve bone mineral density and increase bone mass over time. In fact, the consumption of soy has been shown to be even more effective than pharmaceutical treatment on increasing bone density!⁴
Compare this to dairy products, which in conventional wisdom are hailed as the secret to building strong bones. However, in a 12 year study of over 70,000 women, dairy consumption was actually shown to increase the overall risk of osteoporosis and fractures.⁵
Looking at the evidence, it is clear to see that traditionally prepared soy comes with many impressive health benefits. But what about the other forms of soy so common in our food supply today?
Soy in the West
In more recent times, soy has also found it’s way into Western diets.
Due to the versatility and the cheap cost of production, soy has become a favourite ingredient of almost all major food manufacturers. Soy can be found in a wide range of processed foods including drinks, sauces, dressings, meat replacements, sweets and chocolate… meaning that millions of people are consuming a lot of soy without even realising it!
The problem here is that the soy found in these processed foods comes in the form of highly refined, isolated soy. This comes with none of the benefits of whole soybeans and may in fact pose certain health risks.
The USA is the world’s largest producer of soy, however most of this crop is used to produce soybean oil. The oil is extracted at an extremely high heat using the chemical solvent hexane, which oxidises the fatty acids and makes them unsafe for consumption. Oxidised fatty acids like those found in soybean oil have been shown to convert to free radicals in the human body, which contribute to premature aging, disease, and even various cancers.⁶⁷⁸
In order to increase crop yield, over 90% of the soy grown in the USA is genetically modified and sprayed with the herbicide Roundup, which has also been shown to have adverse health consequences⁹. Conventionally grown soybeans have been shown to contain one of the highest concentrations of pesticides compared to any other food.
It is for these reasons that I recommend consuming organic, minimally processed forms of soy such as edamame, tempeh, fermented tofu, traditionally prepared soy sauce, natto and miso; and avoiding refined soy products wherever possible.
Soy and Hormonal Health
One of the major concerns about soy is the theory that it may have adverse effects on our hormonal health. Men are especially concerned about soy consumption, thanks to rumours that eating it would decrease testosterone levels or otherwise make us less masculine.
There is no credible scientific evidence that backs up this theory. In fact, in the most comprehensive study of its kind analysing all of the research to date, soy was proven to have ‘zero feminising effects on men’ even when consumed at levels that are ‘considerably higher than typical Asian males.’¹⁰
The phytoestrogens in soy have been shown to cause no significant changes in testosterone, free testosterone, estrogen, sex hormone binding globulin protein, or semen quality in men.¹¹
Compare this with actual mammalian estrogen, found in significant levels of cow’s milk. This form of estrogen has been shown to create feminising effects in males and can contribute to gynecomastia (the growth of breast tissue in men).¹²
Soy is just one of many common foods that contain phytoestrogens; along with flax seeds, apples, carrots, coffee, oats, lentils and yams.
Even if you completely avoid soy it is very likely that you are still consuming phytoestrogens. But this is not a problem. Phytoestrogens are a very powerful form of antioxidant which have been shown to have preventative effects against various cancers and other diseases.¹³
The bottom line is that the phytoestrogens in soy will not cause any hormonal imbalances in otherwise healthy individuals, but may well contribute to a number of positive health benefits.
Soy and Thyroid health
When it comes to thyroid health, soy has been shown to contain goitrogenic compounds, much like broccoli, cauliflower, kale and flax seeds. In people with a low iodine intake, goitrogens may interfere with normal thyroid function.
It is for this reason that some people recommend avoiding soy when you have an existing thyroid issue. However, according to Dr Greger of nutritonfacts.org and best-selling author of How Not To Die, the best approach is not to avoid these extremely healthy foods; rather to increase your iodine intake. This can be achieved by eating iodine rich sea vegetables such as kelp, nori and dulse.
When iodine levels are optimal, soy has not been shown to have any negative impact on thyroid health.
What about the environment?
One of the leading arguments against soy is the impact it has on the environment, particularly on the destruction of the Amazon rainforest.
Approximately 29% of Brazil’s greenhouse gas emissions are a result of deforestation related to soy production. This is a HUGE concern.
However, the vast majority of soy grown worldwide is not actually grown for humans! Over 80% of the worldwide soy crop is used to feed animals such as cows, pigs and chickens. Some of the rest is used in the industrial, pharmaceutical and cosmetic industries. Only 6% of the soy grown worldwide is consumed by humans.
And as we discussed earlier, that 6% isn’t just being used to feed vegans and vegetarians. Most of the soy is being used in processed foods in the form of soy isolate, and to make this requires a lot of waste. Using whole soy beans in the form of tofu or tempeh requires much less soy to be grown.
As the main use of soy is for animal feed, the most sensible way to prevent soy- related deforestation is to stop eating meat.
Did you know that the animals in factory farms around the world eat enough grain to feed 9 billion people? If we all stopped eating meat, we would already have more than enough food to feed the entire planet!
A final word about soy
It is clear that the main reason soy has developed such a bad reputation is because of how it is processed here in the West. But if we eat soy as it was traditionally consumed, we remove the problems and open up the door to a lot of health benefits.
Whether or not you choose to eat soy is totally up to you. It is perfectly possible to be healthy with or without it. There is nothing magical found in soy that cannot be found in other plant based foods.
Personally, I am not the biggest fan of the taste of soy so I eat other legumes more often. Occasionally I'll eat tofu or tempeh, and I use miso and / or soy sauce a few times per week. I try to avoid processed soy in the form of meat replacements and soybean oil wherever possible.
If you still don't want to eat soy, don't sweat it! There are still hundreds of other delicious plant based foods for you to enjoy.
What are your thoughts on soy?