Did you know that the United States is the world’s largest producer of soybeans?
In 2017/18, the US produced a whopping 119.52 million metric tons! That makes soybeans America’s second most sown crop, topped only by corn.
The huge production of soybeans can largely be attributed to agricultural use (to feed livestock for example), but there’s also a rising desire for dairy alternatives and plant-based protein sources in recent years. As a result, soy products like soymilk and tofu have become increasingly popular.
But as is so often the case with trending foods and popular diets, soy products are mired in controversy. Some praise soy for its potential health benefits, which include the prevention of cancer and osteoporosis and a calming effect on menopausal symptoms. But others point to a lack of evidence and even suggest soy products are detrimental to health.
So what are you to believe? Well, in this post I take a deep dive into the most recent, thorough research on soy to deliver a science-backed conclusion! But first, you need to know about the different types of soy.
The Different Types of Soy
Soybeans boast an attribute that’s rather rare for a plant-based food source. They’re a complete protein, which means soybeans contain all the essential amino acids. They’re called essential amino acids because your body can’t produce them itself, so you need to provide them via your diet.
A good start for soy! But there are four main types of soy foods, and some are far better for you than others…
Whole Soy Products
Generally, the term “whole foods” refers to plant-based foods that are as unprocessed and unrefined as possible. In other words, the food is as close to the way it came out of the ground or from the tree when it’s eaten as possible.
Looking at soy foods specifically, the true whole food versions are soybeans and edamame beans. (Did you know edamame beans are immature soybeans that haven’t ripened?)
But I also class tofu as a whole food soy product too. Granted,
Fermenting soybeans requires a combination of yeast, mold, and bacteria. The end product is a food product with altered texture, taste, and aroma.
Examples of fermented soy products include:
- Miso – A thick soybean paste popular in Japanese cuisine. Miso soup is probably the most recognized use of miso in the Western world.
- Tempeh – A chewy, cake-like form created by fermenting soybeans with fungus. Tempeh originated in Indonesia, but has become a popular meat alternative around the world.
- Soy Sauce – Perhaps the most recognizable fermented soy product of all! Soy sauce is made by combining a fermented soybean paste with roasted grains and bacteria, and pressing the mixture to extract the liquid.
- Natto – A sticky and undeniably smelly soybean paste popular in Japanese cuisine. If you can get past the smell and acquired taste, natto provides a very unique benefit for your bones…
Natto is the richest food source of vitamin K2 on the planet! Why is that so important? Because vitamin K2 directs the calcium you consume to where you need it– your bones– and keeps it out of the places you don’t want it– your soft tissue, arteries, and organs!
Another important thing to note with fermented soybean foods is the reduced level of phytic acid. Phytic acid is present in legumes (like soybeans) grains, nuts, and seeds. Now, phytic acid is commonly referred to as “the antinutrient” because it interferes with the absorption of many minerals, including calcium, magnesium, and iron.
Soy-Based Processed Food
As you can imagine, soy-based processed foods are almost the opposite of whole food soy products.
These processed products include soy-based meat alternatives like soy sausages, soy burgers, and even soy chicken imitations and soy-based cheeses and yogurts too. They start life as a whole food (soybeans or edamame beans) and are heavily processed using chemicals, artificial flavorings, and even acid washing! None of which are healthy for your body!
It’s also worth noting that processed soy foods typically contain a far greater amount of isoflavones than natural soy foods. It’s not unheard of for a processed soy product to contain 80 mg of isoflavones. Isoflavones are a class of phytoestrogens– naturally occurring compounds found in plant sources like soy that can behave like the sex hormone estrogen (we’ll cover isoflavones and why such an enormous intake may not be such a good idea in just a moment.)
To put things into perspective, in Asian countries where the consumption of soy is amongst the highest in the world, the typical isoflavone intake is 15-20 mg a day. In the United States, it’s as low as 2 mg per day!
Soy supplements vary from protein powders, shakes, and even infant formulas.
The common theme here is a protein isolate which is a highly-processed derivative of soy. It’s made by grinding soybeans into flakes and extracting the oil.
Soy Takeaway #1 – Eat whole soy foods whenever you can!
When it comes to types of soy products, the general rule is the same as for most foods. The closer the food is to its original state the better it will be for you. Highly-processed soy foods and soy protein isolate products contain chemicals and artificial ingredients that you want to steer clear of.
With that in mind, my advice is to enjoy whole food soy products and fermented soy products in moderation as part of a balanced diet. They provide more of the nutrients your body needs and less of the garbage it could do without. In fact, many of these foods, like raw soy and edamame beans, tofu, and tempeh, appear on our list of the top calcium-rich foods!
The Research on Soy’s Potential Benefits and Risks
The original interest in soy’s potential health benefits stemmed from geographic epidemiology studies. In layman’s terms, that’s observing the link between a certain population and a certain outcome.
For soy specifically, there was an observation that populations in eastern Asia consume a lot of soy in their diets and have a low incidence of breast cancer, prostate cancer, cardiovascular disease, and bone fractures. What’s more, the women in these populations report fewer menopausal symptoms– like hot flashes.
As can be the issue with epidemiological observations (more on this in just a moment), these positive health benefits were attributed to
Fun Fact: The isoflavones in soy are, in a sense, adaptogens. If a woman’s estrogen levels are too high, then these compounds, which are much less potent than human estrogens, bind to estrogen receptors and prevent estrogen itself from binding. So they lower estrogenic effects. But if a woman’s estrogen levels are very low, then soy isoflavone binding provides a bit of estrogenic activity.
As a result, soy quickly became a new poster child for nutrition. But such a high profile inevitably drew scrutiny, triggering a wave of contradictory and confusing research. So let’s review the research so far to see what we do, or more accurately don’t, know about soy…
The Potential Benefits of Soy
May Lower Cholesterol and Reduce the Risk of Heart Disease
Early research on soy protein sought to uncover whether it had less damaging effects on heart health than traditional animal proteins.
Animal studies showed that soy protein reduced levels of low-density lipoproteins (LDL). LDL is commonly referred to as “bad cholesterol,” as it has heart-damaging properties. But as you’ll know if you’re a regular reader of the AlgaeCal Blog, the results of animal studies shouldn’t be extrapolated to humans without caution. In fact, early human studies did not replicate the findings of the animal studies.
But perhaps the biggest game changer regarding soy and heart health was a meta-analysis of research on the effects of soy on cholesterol published in 1995. (A meta-analysis examines the findings of several studies on the same subject to try to identify common results and themes).
The meta-analysis reviewed 38 controlled studies on human participants. The amount of soy protein consumed by the participants in the studies varied from 18 to 124 grams per day, and averaged 47 grams per day. And it identified a trend that would help shape public opinion on soy…
The common theme across most of the studies (34 out of 38) was that replacing animal protein with soy protein reduced blood cholesterol. The interesting part was that the reduction depended on the degree of hypercholesterolemia (that’s the scientific word for high cholesterol.)
- In participants with severely elevated blood cholesterol (>335 mg/dL), soy protein reduced blood cholesterol by 20%.
- In participants who had cholesterol levels between 259 and 333 mg/dL, there was a 7% reduction in cholesterol.
- In participants who had normal or low blood cholesterol to begin with (<255 mg/dL), there was no significant effect.
In light of the findings from this meta-analysis and other similar research, the US Food and Drug Administration (FDA) felt there was enough evidence to make an important policy change. As of 1999, foods containing at least 6.25 g of soy protein were allowed to be labeled as “protective against coronary heart disease.”
What’s more, the following year, the American Heart Association (AHA) Nutrition Committee released an advisory promoting soy protein for heart health. The AHA cited the same meta-analysis I covered earlier along with similar research. Plus, remember the estrogenic isoflavones in soy? Well, the AHA came to the conclusion that because estrogen can lower LDL cholesterol and increase HDL cholesterol (good cholesterol) isoflavones in soy “presumably work in a similar, although less potent, manner.”
So, soy protein is good for your cholesterol and heart health then? Not so fast…
This “breakthrough” research and the subsequent FDA and AHA approvals were some 20 years ago. And research on soy and cholesterol has evolved since. Several randomized,
Taking further research into account, the FDA issued a statement in 2017 stating that, “our review of that evidence has led us to conclude that the relationship between soy protein and heart disease does not meet the rigorous standard for an FDA-authorized health claim.” At the time of writing, the evidence does not support a cardio protective effect.
Similarly, the AHA reviewed their initial stance on soy too, and released a new advisory stating “ No benefit is evident on HDL cholesterol, triglycerides, lipoprotein(a), or blood pressure. Thus, the direct cardiovascular health benefit of soy protein or isoflavone supplements is minimal at best.”
So for now, it looks as though the link between soy protein and heart health benefits was made a little hastily.
May Reduce Menopause Symptoms
If you recall, isoflavones can have weak estrogenic effects. So early research hypothesized that the isoflavones in soy could have beneficial effects for postmenopausal women– in particular, a reduction in hot flashes.
As you know, women who have gone through menopause have lower levels of estrogen. So the theory was that soy isoflavones could act as a sort of estrogen replacement.
But what does the research say?
Well, the majority of research to date shows soy may well be beneficial for reducing menopausal symptoms to a certain extent.
A meta-analysis of 19 studies found that consuming soy isoflavones for six weeks to 12 months reduced the frequency of hot flashes by 20.6% compared with a placebo.
The same meta-analysis also found that soy isoflavones reduced hot flash severity by 26.2% compared with a placebo. The daily amount of isoflavones consumed varied from 36 mg to 135 mg. And interestingly, supplements that provided more than 18.8 mg of genistein (the most dominant isoflavone in soy) were more than twice as potent at reducing hot flash frequency than lower genistein supplements.
However, the variables in the studies (and the quality of the studies) differed wildly. Things like the number of participants, the length of the studies, and the source of the soy used were inconsistent from one study to the next, which makes pinpointing an exact benefit hard. In fact, the authors of the meta-analysis concluded that “additional studies are needed to further address the complex array of factors that may affect efficacy, such as dose, isoflavone form, baseline hot flash frequency, and treatment duration.”
Speaking of quality studies, a randomized controlled trial (the gold standard of study design) found no significant effects of whole soy or soy isoflavones on menopausal symptoms. Two hundred and seventy Chinese postmenopausal women were randomized to one of three treatment groups:
- The whole soy group- Took 40 g of soy flour a day
- The daidzein group – Took 40 g of low-fat milk powder plus 63 mg of daidzein a day
- The placebo group – Took 40 g of low-fat milk powder a day.
Each group took their designated formula in beverage form for six months. But the whole soy group and daidzein group had minimal effects on menopause symptoms, including hot flashes. In fact, the placebo group saw the most noticeable improvements!
So why did this study have such a different outcome to the majority of previous studies on soy and menopause symptoms? Well, the researchers theorized that the fact that the women in the study were all Asian could have something to do with it. Asian women, in general, experience fewer menopausal symptoms than Western women, so even at the beginning of this study the women weren’t experiencing a huge amount of symptoms.
The potential ‘bad’…
Breast Cancer Risk
Perhaps one of the most commonly debated effects of soy is in relation to cancer. In particular, breast cancer.
As I explained a little earlier, interest in soy was sparked by observations that Asian populations who traditionally consume a large amount of soy have low incidence of cardiovascular disease, menopausal symptoms, and breast cancer.
But as I also touched on earlier, observational studies linking soy intake to reduced risk of breast cancer should be taken with a grain of salt. Just because there is a correlation between two factors, like eating a large amount of soy and low incidences of breast cancer, does not necessarily mean that one is a direct cause of the other. There are hundreds of other variables that aren’t taken into account that could be the real reason for the low incidence of breast cancer. Genetics, dietary factors, and lifestyle habits of soy eaters versus non-eaters are just a few possible confounding variables.
And other studies suggest a possible paradoxical effect; soy may adversely affect the prognosis of breast cancer patients. And once again, it boils down to the isoflavones in soy. Most breast cancers are sensitive to estrogen, which means estrogen can actually fuel tumor growth. And remember, isoflavones can have estrogenic effects.
Numerous animal studies showed that genistein, the dominant isoflavone in soy, stimulates the growth of human breast cancer cells. What’s more, further studies showed that removing genistein from the animals’ diet actually caused the tumors to regress. But as you know, just as observational studies don’t paint a clear picture, neither do animal studies. We just can’t carry the results of studies on mice over to humans. What’s more, these studies use isolated isoflavones, not whole-food soy products. And it’s widely believed that the isolated isoflavones have a vastly different effect than when they’re provided within the complete soy package.
Interestingly, recent research is starting to circle back to the observational studies and suggests that the age a woman begins consuming soy plays a role in how beneficial it can be in terms of preventing breast cancer. But for the time being, as is becoming a trend with soy, there isn’t enough quality human research to draw a definitive answer.
For a little peace of mind, The American Cancer Society states that “current evidence does not suggest that consuming soy foods is likely to have adverse effects on risk of (cancer) recurrence or survival.” But it’s worth noting that they explain the evidence on isoflavone supplements is more limited.
Negative Effect on Thyroid Function
Another concern with soy is a possible adverse effect on thyroid function.
Worries first arose after in vitro research (test tube research) and animal studies linked isolated soy isoflavones to hyperthyroidism (an overactive thyroid gland) and goiter (an enlarged thyroid gland.) But as you know, these study designs can’t be translated to effects on humans without further research. Plus, the key thing to note here is the use of isolated soy isoflavones. In other words, much more potent than you’d find in whole soyfoods.
Recent research suggests even hypothyroid patients needn’t avoid soyfoods. Granted, it seems soyfoods may interfere with the absorption of certain hypothyroidism medications, but this is true of many other plant foods and herbs. Even so, most thyroid medication can be taken on an empty stomach, so as long as soyfoods and thyroid medications are staggered, there should be no issues.
Over 90% of Soy is Genetically Modified
Did you know that 93% of soybeans grown in the United States are genetically modified organisms (GMO)?
That means that the soybeans have been engineered to produce desirable characteristics like greater resistance to disease or higher crop yield for example. This is done in a laboratory by inserting a desired gene from an external source like a virus, bacteria, or other plant specimen into a plant cell, and growing a new plant from it.
Greater resistance to disease and higher crop yield sound like good things though, so why am I discussing GMO in the “potential bad” section of this post? Well, there are two main reasons:
1. The jury is still out on the safety of GMO
The Food and Drug Administration (FDA) does evaluate genetically engineered food produce, but this is a point of contention. The FDA allows the company that develops the food product to carry out a safety assessment themselves, and then simply reviews this safety assessment afterwards.
This is where things get a little murky because independent studies on the effects of GMO foods on animals have found worrying findings. Findings like infertility, unusual pregnancies, and even death. But studies carried out by companies producing GMO foods consistently find no harmful effects.
Until we know with 100% confidence that GMO products are safe for human consumption, why play the guinea pig?
2. Many GMOs contain traces of pesticides
To make GMO crops resistant to pests, they are bred to actually contain or produce pesticides. One of the most common of which is glyphosate.
Now, since glyphosate was first introduced in the 1970s, all regulatory assessments have established that it has a low hazard potential to mammals. But in 2015, the International Agency for Research on Cancer (IARC) concluded that glyphosate is “probably carcinogenic.”
An EU assessment and World Health Organization (WHO) evaluation didn’t come to the same conclusion. But once again, until we know with 100% certainty, why risk it? What’s more, pesticides can promote chronic, low-grade inflammation in your body. Left unchecked, this is a recipe for bone loss!
Soy takeaway #2 – If you do consume soy, opt for organic!
My advice is to buy organically-grown produce whenever possible. And I stand by that advice when it comes to soy products. We just don’t know enough about GMO produce yet to make a fully informed decision, so it’s best to play it safe.
Soy research roundup
Soy was thrust into the limelight with great promise for benefits for cardiovascular health and menopausal symptoms. But conclusions were drawn from weak studies and observations of Asian populations. More thorough research has failed to draw definitive conclusions, and the truth is that we need more quality, human studies to settle the score.
As far as the negative implications of soy are concerned, the story is much the same. Theories were drawn from inadequate research and observational studies and snowballed into commonly held beliefs. More comprehensive research is still needed, but, at least in terms of thyroid function, it seems soy was falsely accused.
Soy and Bone Health
The last potential health implication of soy I want to discuss is a positive effect on bone health. Like the rest of the touted health benefits of soy, interest was derived from observations of Asian populations.
Postmenopausal Asian women tend to have fewer incidences of osteoporosis, and also fewer bone fractures compared to postmenopausal Western women. And postmenopausal Asian women also tend to consume far greater amounts of soy compared to postmenopausal Western women. (As you’re now well aware, observations shouldn’t be taken as gospel).
And once again, the specific aspect of soy in question is the isoflavones it contains. Estrogen is an important factor in bone health (you can read all about it on our “Top Causes of Osteoporosis” page). After a woman goes through menopause, her levels of estrogen are permanently lower (unless she receives bioidentical hormone replacement therapy)– an important factor in postmenopausal bone loss. So, once again, the theory is that soy isoflavones, which have mild estrogenic effects, can help replace the lost estrogen and help reduce bone loss as a result.
However, as is the frustrating reality when it comes to soy, the current research is conflicting. I’ve pored through dozens of relevant studies, and below is a summary of what the best quality studies (in terms of study design, participant number and study length) show.
P.s. If you’d like to review all the research on soy and bone health that I looked over, you can find it in the tap to expand section a little further down the page.
The first study to mention here has some long, technical words. So let’s explain what they are first. Now, receptor activator of nuclear factor-kappaB ligand (RANKL) basically kick starts a chain of anti-inflammatory reactions which results in your bone resorbing osteoclasts being activated. Not good news! But osteoprotegerin (OPG) binds to RANKL and prevents it from beginning the chain of reactions. So in short, you want a good balance of these two to maintain healthy bones. And that’s where soy comes in…
A two year-long placebo-controlled study of 389 osteopenic postmenopausal women in Italy found that genistein consumption resulted in lower RANKL and higher osteoprotegerin OPG levels!
In this study, genistein was given to 198 women and the remaining 191 women received a placebo. (Both the supplement containing genistein and the placebo supplement contained calcium and vitamin D3.) All the women received the same information about healthy diet too.
The results showed that a significant (-0.021) reduction in the RANKL/OPG ratio occurred in the women given genistein, while in the women receiving placebo, the RANKL/OPG ratio worsened (+0.004).
A three-year randomized controlled trial sought to determine the effects of two different doses of soy isoflavones on the bone health of postmenopausal women. The participants, aged 45 to 65, were randomly assigned to one of three groups:
- The control group – 83 women who received only 500 mg of calcium and 600 IU of vitamin D3 daily
- The 80mg group – 87 women who received 80 mg of soy isoflavone as well as the 500 mg of calcium and 600 IU of vitamin D3 daily
- The 120mg group – 85 women who received 120 mg of soy isoflavones as well as the 500 mg of calcium and 600 IU of vitamin D3 daily
*Note: 500 mg of calcium is a long way short of the recommended 1200 mg a day for women this age. Ideally, they’d get an additional 700 mg of calcium from their diets, but this is often unlikely. What’s more, 600 IU of vitamin D3 is unlikely to be adequate too.
But after the three years, all groups saw a decline in bone mineral density (BMD) in their lumbar spine, femur, and neck. The researchers concluded that, “Our results do not show a bone-sparing effect of extracted soy isoflavones.”
However, these results were contradicted by another long-term randomized study which focused on the isoflavone genistein in particular. 389 postmenopausal women were randomly assigned to receive a placebo (191 women) or 54 mg of genistein (198) daily for a year. Both the genistein and placebo tablets contained 500 mg of calcium and 400 IU of vitamin D too.
As we saw in the previous study, 500 mg of supplemental calcium falls way short of the recommended 1200 mg a day. And 400 IU of vitamin D is woefully short too, so it’s unlikely these made an impact on the results. Besides, both groups received the extra calcium and vitamin D, so if they benefited the BMD of one group you’d expect them to benefit the other group too.
But after 24 months, the women who took the genistein saw increased BMD in their lumbar spine and femoral neck, while the women who took the placebo saw decreases compared to their baseline values.
Similarly, meta analyses of randomized controlled trials investigating the effects of soy on bone health have returned conflicting findings. One review looked at 10 randomized controlled trials that used a mean dose of 87 mg of soy isoflavones and lasted at least one year. The conclusion? “Soy isoflavone supplementation is unlikely to have significant favorable on BMD at the lumbar spine and hip in women.”
Yet another meta analysis, which also reviewed 10 randomized controlled trials, came to a very different conclusion. This analysis showed that consuming between 4.4 and 150 mg soy isoflavones per day for at least 3 months had a positive effect on spinal BMD.
The spine bone mineral density in subjects who consumed isoflavones increased by 20.6mg/cm2 in comparison to subjects who didn’t consume isoflavones. What’s more, this analysis showed that a higher level of isoflavones and a longer consumption period had more significant effects. Increases in spine BMD with isoflavone intake of more than 90mg/day and with treatment lasting 6 months were 28.5mg/cm2 and 27mg/cm2 respectively.
What gives with the contrasting findings?
Researchers tend to agree that the contrasting findings on soy and bone health (and on the other health implications of soy for that matter) can be put down to differing variables.
Differences in study design is one possible reason. Studies have varied in length from just a matter of weeks to several years. What’s more, studies have focused on different types of soy; mixed isoflavone extracts, genistein extracts, soy protein powder, or soy milk, with different dosages of isoflavones.
Plus, the participants have varied too. Most studies are on postmenopausal women, but exact ages, locations, ethnicities, diets, and exercise levels have all varied. All in all, it makes it very difficult to assert that soy is exclusively responsible for any benefit.
For now, research leans towards soy providing a subtle bone health benefit, but most researchers are in agreement that further quality research is still needed. As for very high doses of isoflavones appearing to provide a greater benefit? Well, high doses of isoflavones may be okay for some but NOT okay for others. I suggest you err on the side of caution until a definitive answer is available. If you’re considering supplementing with very large doses of isoflavones, discuss the decision with your healthcare provider first.
Soy Takeaway #3 – Consuming organic soy in low-moderate amounts (like in your coffee, on salads, and in soups) is safe and may be beneficial for bones.
Takeaways of Soy
The research on soy is still inconclusive. It seems the isoflavones in soy could provide subtle health benefits, including for bone health, but until we know for definite, employing a little common sense is likely the best approach. Like most things diet related, balance is key. You wouldn’t get 100% of your protein from beef alone, and the same principle should be applied to soy.
A diverse, balanced diet that provides a variety of nutrients is key to your overall health and your bone health. And don’t forget, we’re all very different. Some of us will tolerate soy well, while others can be allergic! So listen to your body, it knows best.
With that in mind, if you like soy and want to incorporate it in your diet, I suggest applying the three soy takeaways highlighted throughout this post:
- Eat whole soy foods whenever you can!
- If you do consume soy, opt for organic!
- Consuming organic soy in low-moderate amounts (like in your coffee, on salads, and in soups) is safe and may be beneficial for bones.