One of the most common notions people have when thinking of a vegan diet is eating lettuce and large blogs of plain tofu. Doesn’t sound really enticing and luckily also doesn’t represent plant-based eating in the slightest. Along with this naive, yet funny, picture that might come to the uneducated mind is the health concern surrounding tofu & co. With this article, we want to answer questions like “Is soy bad for you” and “Do you have to eat tofu as a vegan”?
Since soy is such a common ingredient in plant-based diets, we need to address the many misconceptions around this food. As a traditional Asian staple food, most know it from dishes like vegetable stir-fries before the veggie burgers have taken over the supermarket shelves.
The health-concerned person might do everything to steer clear of any soy in their diet due to all the myths surrounding this plant-based protein.
In reality, though, these concerns are simply the result of outdated research or misinterpreted results. Unfortunately, many widely circulated beliefs deter people from eating soy and instead, stick to eating high-fat animal products - which isn’t the right way to go about this at all.
So, is soy actually bad for you? We aim to set the record straight here.
What is Soy?
Starting out as the soybean (or Glycine Max), soy is primarily a legume, native to East Asia. It is higher in fat than most beans or lentils, but lower in carbohydrates and an excellent source of plant protein.
In the Okinawan diet, soy is associated with longevity - particularly fermented soy like miso soup and tofu. Soy can be found in many forms, including tofu, tempeh, miso paste or soup, edamame beans, soy yogurt, milk, cheese or ice cream, and veggies burgers and fake meats.
It is this variance in soy and its many forms that have created so much confusion as to whether it is actually healthy or not. The truth is that not all soy is made equal - but we’ll get to that shortly.
The Controversies Around Soy
One of the main concerns around soy involves isoflavones, which much of today’s soy naturally contains. These isoflavones a type of phytoestrogens, which have been described as ‘estrogen mimickers’ in the body and blamed for all kinds of potential consequences.
Especially for men, it is falsely believed that the consumption of phytoestrogens could lead to more feminine characteristics developing in the body - namely gynecomastia (otherwise known as 'man boobs')! Potential infertility has also been a worry.
However, there is currently very little (practically none) evidence to support these beliefs. The assumption that plant estrogens (phytoestrogens) perform the same way as mammalian estrogens is just that - an assumption.
Though plant estrogens are structurally similar to mammalian estrogen, they cannot be created by the human endocrine system, and functionally, they are only weakly estrogenic. By occupying our estrogen receptors, phytoestrogens actually lower the estrogen levels in our blood instead of raising it!
In just one case found where a 60-year-old man had developed gynecomastia, he was drinking a whopping ¾ gallon of soy milk a day. After being advised to cut this down, his ‘condition’ was very easily reversed.
Another popular belief is the negative impact on infants who may be fed soy formula from a young age if they’re unable to tolerate cow’s milk formula. But this too was put to rest in a 2004 Italian study, which found no gynecomastia, no altered onset of puberty, no bone structure changes and no hormone fluctuations in infants raised on a soy formula.
For women, it is worried that an increased intake of estrogen could increase their risk of breast cancer, cervical cancer, PCOS and other hormone imbalance-related disorders.
However, this assumption once again ignores the fact that phytoestrogens are different to mammalian estrogens. In fact, it has actually been shown that phytoestrogens can bring benefits to the body by ‘blocking’ actual estrogen and reducing the risk of breast cancer.
It’s also worth noting that soy isn’t the only food that contains phytoestrogens. These types of plant estrogens are also prevalent in coffee, apples, oats, beans, beer, mint, rice, carrots and flax seeds, to name a few. So if avoiding phytoestrogens was the aim...you’d have to cut out a whole lot of foods!
Animal Estrogen vs. Plant Estrogen
Something that many people forget when being wary of phytoestrogens is that animal products contain actual mammalian estrogen, which can have an effect on the body.
As it happens, humans are exposed to natural estrogen from all kinds of ways - such as through drinking water via excretion through women’s urine. But animal product consumption remains by far the highest way. According to NutritionFacts.org, a child’s exposure to estrogens in drinking water is about 150 times lower than exposure from cow’s milk.
Compare this with plant estrogens, which, as we talked about earlier, are naturally occurring plant compounds shown to have a very weak effect on the body.
Soy and the Thyroid
Regular intake of soy has also been linked with thyroid problems in women. Larrian Gillespie, author of The Menopause Diet, warns of ‘estrogen-like’ substances in soy having a dampening effect on the function of the thyroid. It is believed that menopausal women, who are already prone to hypothyroidism, are particularly at risk.
But several studies have since disproved the causal relationship between soy and lowered thyroid function, due to the protective nature of isoflavones. Studies involving rats, pigs and humans demonstrated decreased thyroid peroxidase (an enzyme that helps formulate thyroid hormone) when fed two different isoflavones from soy. However, no overall negative impact on thyroid function was found.
It’s also interesting to note that humans and rats with demonstrated hypothyroidism also happened to iodine depleted - another known causal factor. So adequate iodine intake also plays a part.
Soy Intake and Animal Products
For camps that advise against the consumption of soy (like advocates of the paleo diet), it is likely their preferred source of protein will be meat, fish, and dairy.
However, the irony is that these people are likely consuming soy without even knowing it. According to WWF, only a small portion of soy is consumed directly by humans, with the majority (almost 85%) being crushed and used as feed for poultry, pork, cattle and even farmed fish.
Furthermore, this type of soy is nearly always genetically modified - the type that some health experts warn against eating.
Due to the increase of the Western world’s demand for meat, soy harvesting has increased massively and is now contributing to deforestation and loss of valuable ecosystems in Latin America.
So the answer to avoiding soy or limiting deforestation isn’t to eat less soy...but rather, to eat fewer animal products.
The Deal with Soy Protein Isolate
A large number of studies that have found negative effects of soy have nearly always been done with soy protein isolate - a processed form of soy.
Soy protein isolate (SPI) is made from extracting the fat from soybeans to leave only the protein component. It is commonly used to make veggie burgers and faux meat products, but can also be found in cereals, soups, energy bars, candy and more.
Soy protein isolate isn’t necessarily bad for you, but the way it is made has been a cause of concern for some.
Most SPI is made with a process called hexane extraction. Hexane is a petroleum byproduct of gasoline refining, also used in cleaning agents and as a solvent for glues, inks, and varnishes.
The beans are first soaked in a hexane bath to remove the fat. Then, the ‘defatted’ soy is soaked in ethanol/acidic waters to remove carbohydrates and flavor compounds. The result is a food that is 90% protein.
Hexane, of course, isn’t the only way to make SPI. But it is the cheapest and fastest. Though hexane extraction has been used in food production for over 70 years, there have been a few health risks associated with it in the past.
The CDC classifies hexane as a neurotoxin, with risks ranging from skin irritation and drowsiness to organ damage, lowered fertility and fatality if swallowed (UN GHS system). The FDA currently has no limit on how much hexane residue is allowed in foods (the EU, meanwhile, allows 30 ppm). This all makes it a bit scary to eat soy protein isolate, as we don’t yet fully know the effects of hexane on the body.
Many brands, such as Amy’s Kitchen, have committed to using only hexane-free soy protein isolate in their foods, providing plenty of choice for consumers. And if you want to avoid soy protein isolate entirely, there are plenty of whole, unprocessed versions of soy to enjoy such as miso, tempeh, tofu, edamame, and organic soy milk and yogurt.
The Health Benefits of Soy
Moving onto the more uplifting stuff, there are of course plenty of reasons to eat soy.
Soy contains all the essential amino acids, as well as being a fantastic source of lean protein with fiber and omegas 3 and 6. It is also full of minerals such as calcium, iron, magnesium, manganese, phosphorus, potassium, and vitamins B1, B2, B3, B5, B6, B9, C, and zinc.
Instead of causing cancer, soy has actually long been shown to protect against cancer, due to the highly protective nature of isoflavones. This is especially relevant to the prevention of premenopausal breast cancer, due to the isoflavones’ ability to block estrogen in breast tissue.
And though there continues to be conflicting studies on the topic, one study of breast cancer survivors from China and the US showed a significant association between soy and reduced breast cancer recurrence.
Phytonutrients, found in abundance in soy, are also commended for helping to prevent disease and keep the body working properly. There are more than 25,000 phytonutrients found in plant foods - one of which is phytoestrogens!
Soy is high in isoflavones, a type of phytoestrogen that has been linked with lower risks of endometrial cancer and bone loss in women.
Any ‘anti-nutrients’ in soy are deactivated during cooking and fermentation, and its content of phytic acid has been shown to have anti-cancer effects in animal models for both colon and breast cancer.
People living in countries with more soy in their diets, like Japan, tend to have a lower risk of heart attacks. Experimental research also consistently shows a decrease in total and ‘bad’ LDL cholesterol, with an increase of ‘good’ HDL cholesterol for those who eat more soy.
It’s worth noting that Alzheimer's disease and other forms of dementia are also less common in Asian populations, where soy is regularly consumed.
Overall, soy is always going to be a healthier substitution for meat, dairy, and eggs. It is always going to be lower in fat, cholesterol, and synthetic or mammalian hormones. Not to mention it’s also a better choice for the animals, and for the environment.
See how it stacks up against animal protein here:
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How Much Soy Should You Eat?
Different experts have different opinions on how much soy we should be eating, but it all averages out more or less the same message.
Dr. McDougall argues for small amounts of traditional soy foods over large quantities of processed or synthetic soy. For example: ‘soy milk to moisten cereal instead of glassfuls as a beverage; tofu pieces in a stir fry over a soy burger; occasional tofu-based dessert over a daily soy ‘candy’ snack’.
Nutritionist Mark Messina PhD, meanwhile, recommends a daily serving of soy, such as one cup of soy milk or 3 to 4 ounces of tofu.
“If in 20 years researchers have found no benefits to soy, then you’ve lost nothing. If they do find some benefits, then you’ve got a great trade-off”, he says.
Many experts advise to continue eating soy as part of a well-balanced diet but don’t eat it for breakfast, lunch, and dinner.
And many recommend sticking to non-GMO, whole versions of soy, such as miso, edamame, tempeh, organic tofu, organic soy milk and organic soy yogurt. Ginny Messina, RD, says she still enjoys soy regularly, alongside a variety of other healthful foods.
Let's sum up the most important findings...
- Soy can readily be enjoyed as a great source of protein, vitamins, and minerals, as part of a varied diet with plenty of fruits and vegetables.
- Soy doesn’t need to be eaten in large amounts to get the benefits but getting a little overboard won't hurt you, either.
- Whole, unprocessed or fermented forms of soy are best, whilst soy burgers, meats, and cheeses should be enjoyed occasionally as a treat.
- If you’re worried about soy protein isolate and hexane content, go for organic products that commit to not using hexane extraction.
- If a vegan woman is worried about thyroid health, she should ensure an adequate amount of iodine in her diet.
Do you enjoy soy regularly or have you been trying to avoid it? Has your feeling towards this legume recently after reading our article? And which soy products do you like the most? Let us know in the comments below.
Alena has been eating a plant-based diet for 6 years and is passionate about sharing her learnings in the fields of nutrition, wellbeing, and vegan ethics. She is the co-creator of nutriciously and loves music, reading, nature, traveling, yoga & good food. Alena received training in the fields of nutrition, music therapy, and social work.