If one natural food source were to earn the title of "controversial food of the year," it'd be soy.
And not only would it have won the title in 2007, it would've held that dubious position for the last three years running.
Why was soy promoted as a nutritional wonder only to fall from grace, stimulating radical, and often diametrically opposed opinions from experts and nutrition buffs across the globe?
Why have recreational exercisers and internet posters on every site imaginable begun to either champion soy or denigrate its value as a viable food option?
And finally, with all the hullabaloo, all the back and forth, all the controversy, why aren't people capable of having an objective discussion about the value soy may or may not have?
Well, these are all questions we've been wondering about.
So, we turned to the research. We interviewed a host of soy experts on both sides of the fence. And from our in-depth research, came this article. Hopefully, it helps you sort through the big soy protein controversy, leaving you with some practical strategies for soy consumption.
A Brief History of Soy
Some of the first crops grown – way back in the 11th century BC – were soybeans. These beans are native to East Asia, and it's no surprise that Asian cultures are known as innovators when it comes to soy products.
The three most important foods derived from soy are things that are fairly common nowadays like miso, tofu, and tempeh. Interestingly, these foods have long been considered as both a source of nutrition and medicine in East Asia.
It wasn't until the early 1700's that soy was introduced to Europe. Shortly thereafter, in 1765, the first soybean plant was grown in North America.
Soy was initially grown in North American to feed animals. It didn't become a human food crop until the early 1900's. My, how times have changed. Today, 55% of total soy production originates in the United States.
However, what's grown today ain't your grandmother's soy.
Genetically modified soybeans were introduced in 1995. These modifications were made to reinforce the crop against pests as well as against the chemicals farmers spray to prevent weed growth (think Round-Up).
Interestingly, about 13 years later, about 90% of the soybeans produced are genetically modified in one way or another.
What's in This Mean Bean?
In terms of protein content, the soybean is roughly 41% protein. And the PDCAA score (a measure of protein quality) for soybeans is just below 1.0, with soy protein isolate at 1.0. Since 1.0 is the highest score a protein can get, soy ranks right up there with milk, beef, and eggs.
When breaking down the specific amino acids, soy is rich in branched chain amino acids, lysine, and arginine, while being low in methionine and cysteine. To this end, soy protein is still "complete" in terms of the full amino acid profile. However, due to the lower methionine and cysteine content, it's marginal in this regard. Some experts consider soy a touch inferior to animal-based proteins.
"I call this one 'Dinner.'"
In terms of dietary fat, the ratio of omega-3 to omega-6 fatty acids in soybeans is about 1:7, which is sensible. Especially when compared to oils like sunflower and peanut, which are 1:100+.
Finally, soybeans contain a mix of slow-digesting carbohydrates. With fiber and other starches that may be good for promoting the growth of healthy bacteria in the gut, soy could be considered gastrointestinal-friendly (assuming no soy maldigestion or allergy).
Is Anyone Actually Eating Soy?
Contrary to popular belief, cultural observation tells us that most traditional cuisines – even Asian – don't incorporate soy as a staple.
The average soy intake in East Asian populations is between 40 to 90 grams per day (1.5 to 3 ounces). Folks, that's totalsoy intake, not grams of soy protein. This amount of soy equates to roughly 10 to 20 grams of soy protein per day, which is actually less than the daily allowance of protein recommended by the FDA.
In these cultures, soy is generally used as an occasional meat replacement or as a condiment to the main dish. In China, tofu has been nicknamed "the meat without bones," because of its versatility in creating so many meat-like replacement products.
Collect 'em all.
In North America, unfortunately, refined soy foods – things like soy concentrates, textured soy, soy lecithin, etc. – are finding their way into more foods on supermarket shelves. Also unfortunate, they're becoming what people equate with soy consumption.
Between 2000 and 2007, United States food manufacturers introduced over 2,700 new foods with soy as an ingredient. As you might guess, most of the soy foods being sold in North American are heavily processed.
In case you're interested, this chart identifies the types of soy foods being sold over the past two decades.
The Whole Soy Story
Kaayla T. Daniel, PhD, wrote a very controversial book, The Whole Soy Story, all about soy. Her book and related interviews have introduced popular culture to a host of valid points about the potential dangers of excessive soy intake.
Unfortunately, rather than understanding the context, after reading one of her books or interviews, most people will take a big step back from soy based foods. However, even Dr. Daniel has been very clear to note that a soy intake similar to that of Asian cultures is healthy and doesn't pose danger.
Dr. Daniel has also stated that old fashioned soy products such as miso, tempeh, natto, and soy sauce are fine when eaten occasionally. In fact, Dr. Daniel even confided in us personally that she and her children include them in their diets.
These products are encouraged by Dr. Daniel because they're fermented. The fermentation process in these soy foods can deactivate specific anti-nutrients, which are substances that cause digestive distress and mineral loss.
We caught up with Dr. Daniel recently, and this is what she said:
"Asia is a huge continent with many different dietary patterns and lifestyles. However, soy is always eaten in small quantities as a condiment in the diet and not as a staple food.
"For most people, I do recommend soy foods made with organic soybeans. But, it's important for people to understand that all soybeans, organic and otherwise, contain phytoestrogens and anti-nutrients. Thus, people put themselves at risk for health problems if they consume soy milk, veggie burgers, and other unfermented soy products, whether or not they buy organic."
The day we contacted Dr. Daniel, she had just finished filing a petition with the FDA asking them to retract their claim that soy is "heart healthy." You can find additional information here.
Another expert many of you may know, Cassandra Forsythe, PhD(c), author of The Perfect Body Diet, recently shared her thoughts as well.
Although she used to have the belief that soy, and all soy-related products, were detrimental to health and the achievement of an ideal body composition, she's revised her position.
She now feels that occasional soy protein consumption may not have such effects. Forsythe has also indicated that manufactured soy protein may have different effects than traditional soy foods, such as whole bean edamame.
But Doesn't Soy Decrease Testosterone?
At this point, we want to dig into some interesting research.
Specifically, let's take a look at a three-month study looking at the effects of different protein types on body composition during a strength training program.
In this study, the researchers provided daily supplements containing 50 grams of a variety of proteins – either soy concentrate, soy isolate, a soy isolate/whey blend, or a whey blend.
Twenty participants added these supplements, in conjunction with a resistance training program. At the end of the three months, a significant increase in muscle mass was noticed with all of the protein supplemented groups. Interestingly, no significant differences were found among Testosterone, body fat, or body weight between the groups.
In the end, the authors concluded that 12 weeks of soy protein supplementation (50 grams per day) was as effective as the other protein types when it comes to boosting muscle mass during a strength training program.
Interestingly, as some people have suggested, soy supplementation doesn't seem to decrease Testosterone or limit lean body mass gains. It's important to note that similar studies have been done using soy-containing supplemental nutrition bars, and the results have been consistent.
In another study using rats and endurance exercise, the authors concluded that protein synthesis was comparable between rats fed different protein-containing meals after exercise – including soy.
In yet another study, researchers found that elite gymnasts supplementing with soy protein (1 g/kg) for four months, saw favorable changes in their stress responses to training (when compared to the gymnasts not using any supplemental protein at all).
Finally, a Romanian study using Olympic athletes supplemented participants with soy protein (1.5 g/kg) for eight weeks. In the end, the authors found that the soy protein supplementation led to increased body mass (approximately 3 kg, mostly from lean body mass) and strength indexes. Significant decreases of fatigue were found after training sessions. No negative side effects or abnormal changes to metabolism were noticed and the product was well tolerated.
Now, before we move on, we want to be clear about one major, important thing. This section isn't designed to promote soy protein supplementation. Not in the least.
However, it's here to demonstrate that when used as part of a sensible training program and varied, calorie sufficient diet, soy protein acts much in the same way that other proteins might act. With increases in lean body mass, decreases in stress hormone responses to training, and improvements in performance.
What About Those Phytoestrogens?
Many exercisers and athletes are concerned that the phytoestrogens (estrogen-like nutrients, such as isoflavones) in soy might be harmful to their health, hormonal profile, and body composition. Well, before discussing this very "applied" issue, let's look at what phytoestrogens really are.
Phytoestrogens (we'll call them "PE's" from now on) are a group of natural estrogen receptor modulators found in various foods, with soy being the predominant source. In plants, these PE's serve as a defense mechanism and natural fungicide.
When soy protein isolates and concentrates are created from soybeans, PE (and phytonutrient) content is diminished due to the alcohol used in extraction. So, many of the PE's are naturally removed during the extraction process. However, some do remain.
The PE's found in soy foods include genistein, daidzein, and glycitein. These PE's are similar in structure to the estrogen hormone, estradiol. As a result, PE's have both weak estrogen-stimulating (estrogenic) and an estrogen-inhibiting (anti-estrogenic) effects, depending on the circumstance.
Phytoestrogens can be good or bad, like a hot date or your crazy ex.
When someone swallows a mouthful of soy, the PE's are modified by intestinal bacteria and taken up into the blood. Once in the blood, these chemicals can weakly attach to the body's estrogen receptors. The body recognizes this binding of its estrogen receptors as a signal to produce less of its own estrogen.
That's one way that soy can actually lowerestrogen production.
Another potential mechanism of PE action in the body is the alteration of circulating estrogen and Testosterone concentrations. These can be altered by the PE's attaching to sex-hormone binding proteins found in the blood.
The UK Committee on Toxicity (2003) noted that PE's bind weakly to the sex-hormone binding proteins and are unlikely to prevent estrogen or androgen binding at normal blood levels.
However, when consumed in high doses, PE's could potentially act as anti-estrogens at the cellular level by competitively binding to estrogen receptors, thus preventing the binding of estrogens that were produced within the body. However, by binding to sex-hormone binding proteins, these PE's could displace estrogens from their blood-bound carriers and free them up to provoke stronger estrogen action in the body.
So, as usual when it comes to biochemistry, there's no clear cut explanation for determining how PE's will function in the body. The actual effects depend on total amount of PE's in the body, receptor binding affinities, and probably a host of genetic factors.
Okay, now that we have some idea (a murky one, at that) of how PE's work in the body, let's look at what the research says regarding how PE's might affect our hormonal action.
One study demonstrated that rats with a high exposure to PE's from soy (20 mg/kg and greater) had lower Testosterone levels. Now, here's the important differentiation point. In the lower dose groups, there were no significant changes to Testosterone (more on this below).
Further, other studies are mixed, showing no change in Testosterone levels, lower Testosterone levels, or with a down regulation of estrogen receptors with high PE's in the blood.
In the end, despite these mixed results and a lack of consensus, there's a common theme: Extremely high levels of PE's have an unfavorable influence on hormone levels, especially when it comes to hormonal status, as well as building muscle and staying lean. However, lower levels don't seem to be problematic.
From Rat to Real Life
Before we go on, let's do something very important – something many authors fail to do. Let's put these rat studies into a real life perspective.
We'll start by looking at an adult male who weighs 190 pounds (86 kg). If he were to consume 20 mg/kg of PE's like the initial rat study indicated, that'd be 86 kg x 20 mg, leading to a total of 1,720 mg of PE's per day.
Do you have any idea how much soy that'd be?!
If not, have a look at the following table. It gives you an idea of the amount of PE's found in soy foods.
Isoflavone content in soy foods.
|Food||Serving||Total Isoflavones (mg)|
|Soy protein concentrate, water wash||3.5 oz||102|
|Soy protein concentrate, alcohol wash||3.5 oz||12|
|Soybeans, cooked||1/2 cup||47|
|Soybeans, dry roasted||1 ounce||37|
|Soy milk||1 cup||30|
|Tofu based yogurt||1/2 cup||21|
|Soybeans, green, cooked (edamame)||1/2 cup||12|
|Soy hot dog||1 hot dog||11|
|Soy sausage||3 links||3|
|Soy cheese, mozzarella||1 oz||2|
As you can see from the table, our hypothetical male is very, very unlikely to consume 1,720 mg of PE's from food.
Check out the following menu:
1 cup of cooked soybeans = 94 mg
6 ounces of tempeh = 74 mg
2 cups of soy milk = 60 mg
6 ounces of tofu = 40 mg
2 soy hot dogs = 22 mg
4 oz of soy cheese = 8 mg
Total = 298 mg
Soy overload, for sure, right?
Yet, it only supplies 289 mg of PE's. That's one-fifth of what might be required to lower Testosterone levels.
So, let's get real here. It's unlikely that Testosterone problems would occur if someone were to eat a moderate amount of whole-food soy products.
A more traditional daily intake of soy for someone may look more like this:
8 ounces of tofu = 53 mg
1/2 cup soy milk = 15 mg
1/2 cup edamame = 12 mg
Total = 80 mg of PE's
No More Rats: Humans and Phytoestrogens
Taking it to human studies, data on patients with prostate cancer showed that the intake of 80 mg/day of PE's didn't significantly alter Testosterone levels.
To go one step further, an intake of PE's up to 16 mg/kg of body weight had no significant influence on behavior or physical characteristics.
Taking the dose up again, another study found that 84 straight days of consuming 450 to 900 mg/day of PE's lowered DHEA levels and had estrogenic side effects in males with prostate cancer. Not necessarily good. However, skim over the chart above to determine how much soy food that'd be. It's a freakin' lot!
I hope you like soybeans.
Revisiting our idea from earlier, the fact that Asian cultures aren't eating tons of soy, dietary PE intake has been reported to be about 65 mg/day in some Asian populations, with the Japanese averaging about 45 mg/day. So, the conclusion seems pretty simple: Small amounts of PE's are probably fine. And small amounts are likely all you'll get with a normal, occasional whole-food soy intake.
Soy and Sperm
Have you ever heard of Dr. Jorge Chavarro?
He and his colleagues from Harvard revealed findings from a study that linked soy-derived foods and PE's to lower sperm concentrations. Not good, right? However, the research didn't find a negative relationship between soy and sperm mobility or sperm quality, which are both key factors to fertility. So, maybe it's not that big of a deal after all.
For this study, the researchers surveyed men on their consumption of 15 soy-based foods during the last three months and didn't directly determine what other foods, medications, supplements, existing medical conditions, sexual activities, or environmental factors may have affected the drop in sperm count.
Many of the study participants were overweight or obese, and males with high levels of body fat produce more estrogen than their lean counterparts. So, in this study, whether it was soy that caused the drop in sperm count or something else is hard to say.
Indeed, Asian populations have regularly consumed soy for generations without fertility disorders. Also, Asian countries have healthy, high functioning children. Dr. Chavarro revealed that East Asian men consume more soy than the participants in his trial and don't develop fertility problems.
Maybe genetics. Maybe something else entirely.
Of course, this research aside, there's a body of research in which controlled amounts of PE's were fed to humans or primates and no negative effects on quantity, quality, or sperm motility were noticed.
Other Dietary Concerns for Hormonal Manipulation
With all of the concern and attention being devoted to soy intake and hormonal changes, we need to remind ourselves that there are other dietary factors that can have an unfavorable impact on hormone levels.
Chronic alcohol intake is one of the most powerful mediators of sex hormone levels. Ethanol is a testicular toxin. Chronic male alcoholics develop an assortment of endocrine disorders, including infertility, testicular shrinkage, and feminization, caused in part by elevated production of estrogens and inhibition of Testosterone biosynthesis in the testis.
Also, alcohol increases the activity of aromatase, an enzyme that converts Testosterone to estrogen in the body.
Heavy drinking can lead to more than just blackouts and questionable hook-ups.
The major source of animal-derived estrogen in the human diet is whole milk and dairy. In the Western world, 60 to 80% of the dietary intake of estrogens originates from whole milk and other dairy products.
In a Western diet, milk is produced predominantly by lactating cattle, and gestation is under the control of steroid hormones, including estrogens. Thus, high levels of milk-borne estrogens can be expected.
The milk that we now consume is quite unlike that which was consumed 100 years ago. Authors have hypothesized that milk is responsible, at least in part, for some male reproductive disorders. Other authors have stated that, "The Western diet (characterized by dairy products and meat) causes a trend of increasing levels of estrogen."
Maternal beef consumption (specifically, beef containing hormones) may also alter a man's testicular development in utero and adversely affect his reproductive capacity.
Well, it's odd that soy is getting hammered for hormonal implications when many of our dietary staples might also have an impact on our hormonal levels if we're not conscientious about ensuring adequate exercise and a varied diet.
Rapid Fire: Soy and Other Health Conditions
Dem bones, dem bones: Soy and other plant proteins have a lower net acid excretion, but it still isn't clear if they have skeletal advantages over animal proteins.
A recent trial in North America looked at the effects of soy protein and moderate exercise on bone health in post-menopausal women. Forty-three post-menopausal women completed the trial. They were given either milk protein or soy protein isolate powder (both including calcium and vitamin D), with or without a supervised moderate exercise program (three times a week) for nine months.
Compared with milk powder placebo, women on soy powder had significant reductions in bone turnover, but not in bone mineral density. High bone turnover leads to a greater propensity for fracture.
Two new meta-analyses from China have looked at the effect of PE's on bones.
In the first meta-analysis, data from ten trials involving 608 menopausal women showed a significant benefit on spine bone mineral density. This was predominantly noticed when PE's were given in higher doses and for longer periods.
In the second meta-analysis, data was combined from nine trials on 432 subjects and showed that PE's significantly increased bone formation and decreased bone resorption.
Body composition: We know that protein is more satiating than carbohydrates and fat. And that higher protein diets seem to be important for a healthy body composition, with soy protein seemingly as effective as other proteins in this regard.
An evidence-based review by Drs. Allison and Cope (University of Alabama at Birmingham), and Dr. Erdman (University of Illinois at Champagne-Urbana), found soy foods equal to other protein sources, such as dairy or meat, in helping to promote fat loss.
The review was published in the November 2007 issue of Obesity Reviews. The review found that individuals lost equivalent amounts of weight (and inches in some cases), using soy protein, dairy milk meal replacements, and beef or pork at equal calorie levels.
Soy and anti-nutrients: Trypsin inhibitors? Phytic acid? No, these aren't characters from the new Shrek movie. These are anti-nutrients found in soy foods. The good news is that they're deactivated by cooking and fermentation. So, consumed cooked and fermented soy foods won't inhibit protein and mineral absorption.
Also, phytic acid may have anti-cancer properties.
Soy and your ticker: The American Heart Association (AHA) gives the "bottom line" about soy on their website:
"Taking soy or isoflavone supplements is unlikely to reduce your risk of heart disease. Yet, eating foods that contain soy protein to replace foods high in animal fats may prove beneficial to heart health."
Plant protein and kidneys: Soy protein, despite being of very high quality, doesn't appear to have the same effect on kidney function that occurs in response to animal proteins. So, if your doc or mom still gets worried about the high protein meals, mix in some soy for good measure.
Based on all of our readings, discussions, and knowledge acquired about soy foods over the past 15 years, it seems that a reasonable amount of unrefined soy intake is fine.
We don't think soy is anything special in terms of disease prevention. Nor do we think it's extremely harmful in your quest for optimal health, body composition, or performance. With that said, we do caution against excessive soy intake. When consumption of soy foods is excessive, there might be some negative effects going on.
To this end, it seems best to avoid isolated and highly refined forms of soy on a regular basis. In other words, things like soy isolates, soy concentrates, textured soy protein, etc. should be minimized in the diet. Whole soybeans, soy milks, tofu, tempeh, and miso, on the other hand, are better options.
In terms of total intake, we'd say one to two servings of soy per day seems to be a safe and potentially healthy intake. Exceeding three servings per day on a regular basis may not be a good idea. For good measure, a serving is one cup of soy milk and four ounces of tofu, tempeh, or soybeans.
It's easy to understand how some individuals can consume excessive amounts of soy. Soy milk on the morning cereal, a soy protein smoothie for a snack, a soy burger at lunch, a handful of soy pretzels here and there, and soy ice cream for dessert. Even a soy novice would recognize that to be overload.
So, don't make the mistake of eating tons of soy – even if you're on a plant based diet.
Watch Out for Food Pushers
While excessive soy consumption gets a bad rap, we often think about the excessive consumption of any one food and the potential negative effects. What about the high intake of alcohol? Or factory-farmed dairy and meat?
Soy is a chief ingredient in the feed of factory-farmed animals. Does this indirectly influence the nutrition of meat-eaters? Should they only purchase grass-fed animals? We hesitate to think that any "mono-food" excess is a good idea on a regular basis.
And, of course, the soy industry does its part (just like the dairy, egg, and beef industries) to create just that – a mono-food culture. They push soy by overstating the benefits and undermining the concerns.
You might be shocked to know that as practicing nutrition consultants, we receive at least one mailing per week from a major food industry telling us to push their particular food on our clients.
We're not making this stuff up, folks.
Of course, these messages get the "delete" treatment just as fast as those annoying penis enlargement emails that sneak past the spam filters.
In the end, as we have often have discussed, there's a simple rule of thumb that most people somehow forget... repeatedly. And it's this: You don't often go wrong with whole, unprocessed foods. Where the problems typically occur is with processed food, in all forms.
This rule of thumb is also true with soy.
Whole, unprocessed soy is just a food. It's not a political agenda. It's not a public health crisis. It's not a way of life. It's not a medicine. And it's not a panacea.
It's one food. One of a few thousand foods people can include in their diets. It's nothing more.
So, as the title of this article hints at, we want people to re-freakin-lax when it comes to soy. Moderate doses of whole-food soy proteins really are no big deal.
Soy and Testosterone
Nutr J 2004;3:22-27.
J Nutr 2007;137:357-362.
J Sports Med Phys Fitness 2001;41:89-94.
Am J Clin Nutr 1991;54:1093-1100.
Proc Soc Exp Biol Med 1995;208:44-50.
J Natl Canc Inst 1996;88:1369-1374.
Toxicol Sci 2001;61:115-127.
Toxicol Sci 1999;51:236-244.
J Chromatogr B Analyt Technol Biomed Life Sci 2002;777:249-260.
Nutr Cancer 2007;59:163-168.
Nutr Cancer 2004;48:160-170.
Am J Clin Nutr 2002;75:126-136.
Nutr Cancer 1999;33:82-87.
J Epidemiol 2000;10:127-135.
J Nutr. 2002 Mar;132:570S-573S. Review.
Indian J Physiol Pharmacol 2006;50:291-296.
Subst Alcohol Actions Misuse 1983;50:291-296.
Alcohol Alcohol Suppl 1987;1:109-116.
Clin Experi Res 2004;5:780-785.
Med Hypotheses 2001;57:510-514.
Med Hypotheses 2004;62:133-142.
Hum Reprod 2007;22:1497-1502.
Soy and Bones
Menopause 2007;14(3 Pt 1):481-488.
Clin Nutr 2008;27:57-64
Eur J Clin Nutr 2008;62:155-161.
Am J Clin Nutr 2005;81:733-735.
Med Hypotheses 2006;66:1093-1114.
J Nutr 2005;135:1243-1247.
Soy and Body Composition
Soy and Heart Health
J Nutr 1998;128:209-213
Atherosclerosis 2007; Nov 16: Epub.
Am J Clin Nutr 2004;80:1391-1396.
Soy and Anti-Nutrients
J Nutr 2003;133(11 Suppl 1):3778S-3784S.
Soy and Thyroid
Biochem Pharmacol 1997;54:1087-1096.
Environ Health Perspect 2002;110 Suppl 3:349-353.
Cancer Epidemiol Biomarkers Prev 2002;11:43-49.
Nutr Rev 2003;61:1-33.