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Soy Foods: The Good, The Bad & The Ugly

Soy may be one of the most controversial foods. Depending on who you talk to, the little, green soybean is either a health panacea or practically as dangerous as the plague.

Scientists are fascinated by soy as well, making it one of the most researched foods out there, with thousands and thousands of studies delving into everything from whether it is safe to eat (it is, but only when cooked) to if it can prevent cancer (who knows? The research is terribly contradictory).
If you delve into the complex and confusing issues surrounding soy, you’ll find that a lot of the controversy centers on a few key pitfalls. By avoiding these drawbacks, soy ceases to be something to get all riled up about.
Soy can be a flavourful, healthful addition to your diet in small quantities. At the same time, if you prefer to avoid soy or just don’t like it, there’s no compelling reason that you should have to eat it. Although it is a high-quality plant-based protein source, it’s not like fish, which everyone is simply better off including in their diet because it is the only robust source of the conditionally essential fatty acids EPA and DHA, which are necessary for optimal health and well being.
Therefore, this article is going to look at the good, the bad, and the ugly of soy foods and leave you with five points for safely including soy in your diet.
The Good
#1: Soy is a high-quality protein. 
Soy is the highest quality plant-based protein, containing all the essential amino acids, including a decent amount of leucine, the most important amino acid for building muscle. Theoretically, this makes soy a great protein source for vegetarians.
#2: Soy is a nutritionally rich food. 
At first glance soy looks like a wonder food, containing a host of phytonutrients, vitamins, and minerals that are needed for peak health. However, soy also contains phytic acid that inhibits the body’s ability to use some of the minerals, especially iron and zinc. There’s also some evidence that when the phytonutrients are processed and consumed in supplement form, they may increase cancer risk, though this research is far from conclusive.
#3: Asians traditionally eat a lot of soy and have lower disease rates. 
People in Asian countries who have a high soy intake tend to be much healthier than westerners. Many of the studies that show a positive effect of soy foods on health are from Asian countries.
#4: Fermented soy is a great source of probiotics.
There are many fermented soy foods such as tempeh, miso, and natto, which provide beneficial bacteria for healthy gut function.
#5: Some studies associate soy intake with lower cancer risk. 
Observational studies show a reduced risk of breast cancer with higher soy intake, especially in Asian countries. However, the results are incredibly confusing and endlessly contradictory.
For instance, one large meta-analysis found that women who ate more soy had a small reduction in breast cancer risk, with a stronger association in pre-menopausal women than post-menopausal. Another study found that post-menopausal women with the highest amount of miso and isoflavones (the antioxidants in soy) in the diet had the lowest breast cancer risk.
To make things more complicated, there are also a host of studies showing no benefit of soy consumption on preventing cancer. As you’ll see in the “Bad” section, there is some evidence that supplementing with the isolated biochemical compounds in soy may increase breast cell growth, which could lead to cancer.
#6: Some studies associate soy intake with lower heart disease risk. 
Soy may reduce heart disease risk, with studies showing that people who eat more soy have lower rates and others showing no effect. For example, in the Shanghai Women’s Study that followed 75,000 women for 3 years, greater soy intake was associated with a lower risk of both death from heart disease and non-fatal heart attack.
On the other hand, a much smaller study of Western women in Europe found no effect of soy intake on heart disease risk. A third study found no association between soy intake and heart disease mortality in 63,257 adults from Singapore.
Additionally, there’s evidence that soy lowers cholesterol, reducing levels of LDL and total cholesterol. And although people have been told that cholesterol levels are associated with heart disease risk in the past, recent studies show they are not as good a predictor as other markers like triglyceride levels. Simply, if soy reduces cholesterol, there is no guarantee this will lead to a decrease in heart disease.
If soy does reduce heart disease risk, it’s likely due to the antioxidants and possibly the fiber it contains. Additionally, it is low-glycemic, which could provide a beneficial effect, reducing inflammation and minimizing fat gain. But these are all benefits you can achieve from a diet high in vegetables and some fruit (two foods that are consistently associated with lower heart disease risk), healthy fats, and high-quality protein. So, there’s no need to eat soy to prevent heart disease if you don’t want to.
#7: Soy may improve bone strength in women.
The isoflavones in soy have a similar chemical structure to ipriflavone, a synthetic drug used in the treatment of osteoporosis. For this reason, soy protein has been investigated in the treatment of osteoporosis, with results showing promise in preventing declines in bone mass in post-menopausal women, while reducing risks to the side effects associated with estrogen replacement therapy.
For example, one observational study found that older Chinese women who ate more soy had higher bone density in the hip and total body than those who ate the least. Bone density values differed by about 4 to 8 percent between the first and fourth soy protein intake quartiles.
However, as promising as this and other studies are for protecting female bone health, other studies haven’t panned out. A 2004 randomized trial that supplemented 175 post-menopausal women with isoflavones for 12 months showed no effect on bone density. The obvious difference is that these women were taking just the antioxidants and not the whole soybean, which may be the difference maker for having a protective effect.
The Bad 
#1: Soybean oil may cause obesity and diabetes.
 Soy makes up a huge number of calories in the American diet and it has been suggested to be contributing to the obesity epidemic. According to a study done on rodents, scientists concluded that soybean oil is causing more obesity and diabetes than fructose—a form of sugar that is thought to contribute to metabolic problems when consumed in large quantities, particularly in liquid form.
The study in question found that a diet high in soybean oil led mice to gain 25 percent more weight than mice on a diet high in coconut oil. Mice on the high-soybean oil diet gained 9 percent more weight than on a high fructose diet.
The soybean oil diet also caused diabetes, inducing glucose intolerance and insulin resistance. This metabolic derangement led to changes in the expression of genes in the liver that metabolize drugs and other foreign compounds that enter the body. This suggests that diets high in soybean oil could affect one’s response to drugs and environmental toxins, if humans show the same response as mice.
#2: American soy intake has skyrocketed in the past 60 years.  
Soy was first introduced as a food product in the U.S. 60 years ago. Our intake of soybean oil has increased by 116,300 percent to 11.6 kg of soybean oil since 1909, and that doesn’t even account for all the soy we get from other soy food such as soy milk, edamame, tofu, or soy that’s added to processed foods.
Soybean oil now accounts for 60 percent of all edible oil consumed in the U.S., and it contributes a whopping 7 percent of calories, which is an increase of over 1000 percent from the 1 percent it supplied in 1909. Being that soybean oil is processed and highly refined, this cannot be a good thing for the health our society.
#3: Soy is like sugar—it’s added to EVERYTHING. 
Things get even more alarming when you realize that the numbers don’t account for all the processed soy that is being added to everything including cereal, bread, and protein bars in order to increase protein since it is so popular to consumers. Soy is also popping up in condiments, ice cream, candy, and baked goods. Naturally, it’s used for meat substitutes and soy milk but you’ll also find it in real processed meats, such as pork sausage.
#4: Soy may inhibit thyroid function.
Similar to compounds found in cruciferous vegetables and corn, soy contains goitrogens, which are substances that interfere with thyroid function by inactivating the enzyme necessary for thyroid hormone release.
But once again, reduced thyroid activity hasn’t been shown in all studies—some studies show no effect.  For example, in one study, soy supplementation had no negative effect on thyroid function, whereas seaweed supplementation did. A second study found no effect of soy protein isolate supplementation on thyroid function in men.
Nonetheless, if you are diagnosed with hypothyroidism, it’s probably a good idea to avoid soy, completely eliminating soy supplements and processed foods containing soy.
The Ugly
#1: Isolated isoflavones may increase cancer risk. 
Soy contains isoflavones such as genistein, daidzein, and glycetein. These compounds mimic estrogen in the body and may disrupt endocrine function.
Originally, it was hypothesized that these isoflavones are the reason some observational studies show lower cancer rates in people who eat more soy foods. Researchers thought that these compounds were protective against breast and prostate cancer because they can bind to hormone receptors, shielding them from naturally occurring estrogen that may cause cancer.
However, other recent research is not so positive. Some studies show that soy isoflavones increase cell proliferation in the breast, which could increase cancer risk, although results are far from conclusive. In one study, about 30 percent of the pre-menopausal women who took soy protein daily had elevated estrogen levels and an increased number of breast epithelial cells after 6 months.
#2: Soy can disrupt hormone function. 
No discussion of soy foods would be fair without considering how they affect hormone levels. As mentioned above, the chemical compounds in soy bind with estrogen receptors in the body, which in simple terms can raise or lower estrogen and testosterone levels in the body. Unfortunately, research into the effects of soy foods on hormone levels is varied and inconclusive.
For example, one study of young women found that isoflavone consumption disrupted the menstrual cycle, with 60 percent experiencing prolonged menstruation and 20 percent having shorter periods. Researchers concluded that soy isoflavones altered estrogen levels and influenced the hypothalamic-gonadal axis, which represents more central changes in the brain and not just in terms of estrogen receptor binding.
There’s also evidence that the estrogenic compounds in soy have different hormonal effects depending on if the women has high or low estrogen levels. In a low-estrogen environment such as that experienced by post-menopausal women, soy foods might activate estrogen receptors, effectively raising estrogen levels and alleviating menopause-related symptoms. But in a naturally high-estrogen environment, such as women of reproductive age, soy foods might block the true estrogen compounds from binding to receptors, thereby decreasing estrogen levels. This could be beneficial for women who suffer from menstrual disturbances, however, more research is needed.
In men, the research is equally confusing. A 2010 review found that soy foods in larger amounts than those typically eaten by Asian men don’t reduce free or total testosterone levels. No feminizing effects were reported. However, a 2013 study of trained young men who supplemented with 20 grams of soy protein for 14 days had a lower testosterone response to an intense workout than when they supplemented with whey protein. There was no effect of soy supplementation on estrogen levels and scientists write that it is an “urban myth” that soy hinders anabolic signaling or increases estrogen levels in men.
A 2005 study found that young men who took a soy protein supplement for two months had lower testosterone and higher estrogen levels than a group that took milk protein isolate. Researchers think this hormonal profile might be beneficial for preventing prostate cancer. Even if it does, it’s doubtful that most men would voluntarily trade lower cancer risk for altered sex hormone levels.
#3: Soy is the most highly sprayed GMO crop. 
If you regularly eat soy or if you are interested in the whole GMO controversy, you probably know that the vast majority of American-grown soy is from GMO seeds. But what does that really mean? Is all the non-organic soy GMO?
According to data from the USDA, the answer is probably. Today, 94 percent of soy is from GMO seeds, whereas in 1996 only about 15 percent of soybeans were GMO. Additionally, soybean seeds tend to be Roundup Ready, which means that they respond extremely well when sprayed with the pesticide Roundup. Although this increases crop yield and drives soy prices down, GMO-soy sprayed with Roundup has been associated with adverse health in some studies.
One way to avoid these issues is to choose organic soy since organic seeds cannot be genetically engineered and they experience lower pesticide exposure than conventional produce.
Take Away Tips
#1: Avoid processed foods in favor of whole foods to reduce your intake of processed soy and soybean oil.
#2: If you do choose to include soy in your diet, whether from soy milk, tofu, edamame, soy protein, or some other form, make sure it is organic. Organic soy foods are not hard to find and tend to be comparable in price to conventional soy.
#3: Organic fermented soy is a great source of probiotics and can add flavor and texture to meals. Including tempeh, miso, tofu, and natto in your diet occasionally in small quantities may be beneficial for gut health.
#4: Assuming you get high-quality protein from other sources, it’s completely reasonable to avoid soy if you choose. As mentioned in the intro, soy doesn’t supply nutrition that can’t be gotten from a diet high in a variety of vegetables, berries, meat, fish, and other antioxidant-rich foods.
#5: Although it’s not as effective as whey, soy supplementation has shown positive outcomes when combined with training for building muscle. Should you use it if you’re allergic to whey?  It’s one option, however, there are other alternatives such as pea, rice, or egg protein that don’t bring the complications of endocrine disruption. Ultimately, this is a personal choice, but if you do choose to supplement, opt for organic soy.
Poliquin