The Joys and Oys of Soy

by Lola Rosewig on February 20, 2013

Image courtesy of RobotSkirts/ www.flickr.com/photos/
hackaday/5334463515/

Soy. What does this word mean to you? Do you think of a healthy vegetarian food choice? Is it the answer to your lactose intolerance? Or have you heard of the suggested estrogenic effects and fear the potential of manboobs?

Don’t fear just yet, but these are some of the things that people associate with consumption of soy foods. This is partly due to the inclination of popular health media being ever eager to latch onto the latest food or nutrient with supposed health benefits or detriments. Soy, and several of its components, have been in the spotlight in the last several years for both of these reasons. So, I decided to explore the science that lay behind the controversy with soy.

It all started in Asia…

The low observed prevalence of obesity and metabolic diseases in Asian countries prompted exploration into the Asian diet for the key to the seemingly miraculous health. Soy features prominently in Asian culinary fare, and drew interest as the possible secret ingredient.

Edamame
Image courtesy of ponsulak / FreeDigitalPhotos.net

You are probably familiar with soy products in their various forms from tofu, soymilk, soy sauce, soybean oil, tempeh (fermented soybean cake), to edamame (cooked immature green soybeans). Soy is also found in many protein bars, soy yogurt and ice cream (dairy alternatives), and veggie burgers and hotdogs (meat alternatives). Soy protein is even fortified in many cereals and baked goods. Soy seems to be everywhere and chances are that you consume it in one form or another.

The question is, “ Is this a good thing?”

Soybeans are a type of legume that is oil-rich, exhibiting a healthy fatty acid profile, is a source of complete protein (meaning that it contains all essential amino acids—rare for a plant protein), and contains many of the B-vitamins, and several minerals including: iron, magnesium, calcium, and potassium.

Beyond this nutrient profile, soybeans contain bioactive phytochemicals (naturally occurring compounds in plants that may have physiological properties). One important group of phytochemicals that has garnered much attention in the media, as well as in the scientific community is the isoflavones. These compounds can have estrogen-like effects by binding to estrogen receptors and have been tenuously linked to adverse outcomes—like the feminization of males who ingest high quantities. Studies on animals have found that dietary soy exposure had caused a decrease in androgen hormones (like testosterone) and decreased prostate weight. However, these results are not generalizable to humans as the dose employed in this rodent study was extremely high—well beyond what would be found in dietary content. Messina in a review in The Journal of Nutrition states that,

 “…the totality of evidence, especially the clinical data, indicate feminization concerns are unwarranted.”

Image courtesy of scottchan / FreeDigitalPhotos.net

So, are there any potential health risks?

Well, there are conflicting results on the effect of soy on breast cancer. A review in Molecular and Cellular Endocrinology explains that there is data of both negative and positive effects on breast cancer cell growth. And there is further research that found an interaction between soy and tamoxifen (a popular breast cancer drug). This suggests that perhaps caution should be applied to those who have, or are at high risk of breast cancer.

Another population with which caution would be advised is infants. There is not much data on long-term effects of either soy-based infant formulas, soy exposure via lactation, or in utero exposure. One study in Hormones and Behavior found adverse effects on reproductive development and spatial learning for male offspring of mothers exposed to isolated soy isoflavones throughout pregnancy and lactation. However, this study was conducted in rodents with an isolated isoflavone which is again not a good representation of human exposure. Despite this, infancy is a vulnerable time in which exposure to any potential endocrine-disrupting substances should be limited when possible.

What about everyone else…are there benefits?

Soy has been shown to have beneficial cardiovascular effects. The cholesterol-lowering effects have been well-enough established for the FDA to issue soy foods the health claim of being protective against coronary heart disease. There are also documented benefits  of reducing high blood pressure (Messina).

And those feared estrogenic effects may actually be responsible for the observed benefit in reducing the frequency and severity of hot flashes in menopausal women as well as increasing bone density in post-menopausal women.

There have also been suggestions that soy and its constituents can help prevent and/or improve obesity. However, at present there is a lot of conflicting data—so no definite conclusions should be drawn just yet.

An interesting point is that the clear health benefits from numerous studies in Asian populations have not been reproduced with the same dramatic results here. There are two proposed explanations for this observation:

First, the way in which soy is consumed in the US tends to be in the form of much more processed foods, often containing components of soy (like isolated isoflavones, or soy protein) as opposed to whole food preparations as traditionally seen in Asian cuisine (Reinwald et al.). By adulterating the soybean, we may be depriving ourselves of some of the health benefits as the isoflavones may act in concert with other phytochemicals and nutrients in soy.

Second, the health benefits seen in Asian populations may be due to lifetime exposures to soy, and not the short-term exposures evaluated in most intervention studies.

Certainly amongst the abundance of literature on soy research, the aforementioned health outcomes are only a few that may be associated with consumption of soy. From what I could find, there are far more health benefits than consequences in the literature. And there is still a need for more research on the topic to clarify many finer points.

In the mean while, to paraphrase a nutritional epidemiology professor of mine:

To determine if a food is “good” or “bad,” you need to ask the question, “Compared to what?”

If eating soy for you means that it replaces red meat in your diet, for example, that would certainly be beneficial because of the reduction in saturated fat. If, however, your version of eating soy means downing soy protein bars that are also sugar-laden for your snacks…well, you’d probably be better off with an apple and a handful of nuts.

Traditional Miso Soup with Tofu
Image courtesy of rakratchada torsap / FreeDigitalPhotos.net

Conclusions…

In the end, there seems to be a place on most people’s plates for soy, if they so choose. There is a lot of fear-driven misinformation in the popular media that you should take with a grain of salt. Of course, if you have specific concerns about your individual health, please consult with your physician. And if you do opt for soy, consider consuming it in more traditional, whole-food forms. I will also reiterate the conventional dietary wisdom of exercising moderation and variety in your diet—after all it’s the spice of life.

 

References:

Ball, E.R., Caniglia, M.K., Wilcox, J.L., Overton, K.A., Burr, M.J., Wolfe, B.D., Sanders, B.J., Wisniewski, A.B., Wrenn, C.C. (2010). Effect of genistein in the maternal diet on reproductive development and spatial learning in male rats. Hormones and Behavior, 57: 313-322. doi:10.1016/j.yhbeh.2009.12.013.

Cederroth, C.R., Nef, S. (2009). Soy, phytoestrogens and metabolism: A review. Molecular and Cellular Endocrinology, 304: 30-42. doi:10.1016/j.mce.2009.02.027.

Messina, M. (2010). Insights gained from 20 years of soy research. The Journal of Nutrition, 140:2289S-2295S. doi:10.3945/jn.110.124107.

Reinwald, S., Akabas, S.R., Weaver, C.M. (2010). Whole versus the piecemeal approach to evaluating soy. The Journal of Nutrition, 140: 2335S-2343S. doi:10.3945/jn.110.124925.

Taku, K., Melby, M., Kronenberg, F., Kurzer, M.S., Messina, M. (2012). Extracted or synthesized soybean isoflavones reduce menopausal hot flash frequency and severity: systematic review and meta-analysis of randomized controlled trials. Menopause: The Journal of the North American Menopause Society, 19(7): 776-790. doi: 10.1097/gme.0b013e3182410159.

Taku, K. Melby, M., Nishi, N., Omori, T., Kurzer, M.S. (2011). Soy isoflavones for osteoporosis: An evidence-based approach. Maturitas, 70: 333-338. doi:10.1016/j.maturitas.2011.09.001.

mark freedman February 21, 2013 at 7:25 am

Very interesting and informative. Thank you!

Lola Rosewig February 21, 2013 at 8:02 am

Thanks for reading!

Vnny February 21, 2013 at 5:13 pm

Whole, non-processed food wins again.

Virginia February 22, 2013 at 9:47 am

I have wondered about the effects of TVP ( vegetable protein) . I believe it is a 100% soy product. It is a convenient substitute for bread crumbs but shy away from it because I am a breast cancer survivor. I wish I could sound intelligent and find errors or misinformation in your blog.

Lola Rosewig February 22, 2013 at 7:09 pm

From what I could find, TVP usually is made from soy protein, but may have other isolated vegetable proteins in the mix. I would check the ingredients label to be sure.
Thank you for reading and adding your comments.

Dana Dolinoy February 23, 2013 at 6:55 pm

Hi Lola, I enjoyed reading your blog – there’s a ton of conflicting evidence indeed. Seems timing, duration, and source of soy “exposure” are also important to consider. Even in rodent studies – the background amount of phytoestrogens can vary from lab to lab and even from diet batch to batch so it’s often hard to compare seemingly similar animal studies. J Thigpen writes about this phenomenon!

Lola February 24, 2013 at 6:54 pm

Hi Dana,
Thanks for reading and commenting! I agree with you that there are many variables to consider in the exposure. In sifting through the vast sea of soy literature, I tried to find some of the key arguments. But of course, being until now completely unfamiliar with this research, I admit it was challenging to evaluate the conflicting perspectives. I will definitely check out what Thigpen has to say. Thanks for the recommendation.

CBD February 24, 2013 at 5:18 pm

I don’t think the average person in the US has any idea how common soy has become in prepared food products. It’s in everything from bread to chocolate to salad dressing. I was surprised to realize this after being diagnosed with a soy allergy. It’s even in body care products, like shampoo! So the question of the effects of soy in different forms really matters — eating soy lecithin and soy oil in food products probably isn’t the same as eating some tempeh with your steamed vegetables. And now we’re even bathing in it.

Lola February 24, 2013 at 6:59 pm

It does seem that soy is rather ubiquitous these day–at least in the US. It seems unnecessary–and in some cases (like yours) actually harmful. I wonder if there will be a point (maybe in 20 years) when we will see the effects of the soy infiltration into our food and other consumer goods. Thanks for contributing!

Soy Oy Indeed February 26, 2013 at 3:20 am

Soy is one of the top eight allergens in the US, and thus one of the ingredients that must be highlighted on food labels so people can avoid it. I gleefully clicked on this link hoping that the “oys” you covered would include the painful consequences of a soy intolerance, which is pretty common. I can’t digest processed soy – tofu, soybean oil, soy milk. It makes me bloat up like a balloon, and I get horrible gas or worse.

Although tofu is easy enough to avoid, soybean oil is in most mayonnaise, and it sneaks into all kinds of surprising places, like pizza, sausage, and popcorn. Soy lecithin doesn’t bother me, which is good, because it’s in almost everything, but it’s also not a soy protein.

Interestingly, miso, tempeh, and soy sauce are all fermented and don’t cause any of these problems in me or my similarly soy-affected friends, and in fact seem to have some digestive benefit (as most fermented foods do). I’m curious as to whether Asians whose diets include lots of soy have different digestive enzymes present in their bodies, or whether the dietary trait people should have studied was not “Gee, they eat more soy,” but “Gee, they eat a lot of fermented foods, including fermented soy.”

Also, when you recommend soy in “traditional, whole-food forms,” what would this include, exactly? Whole soy beans? Bean sprouts?

Lola Rosewig February 27, 2013 at 12:32 pm

You bring up an interesting point about the fermented foods. And I suspect that it may not be a difference in enzymes that allows people of Asian descent to digest soy, but perhaps a difference in gut microbiota. The gut microbiome is a hot area of research right now–trying to characterize the way in which our intestines are colonized with different bacterial strains and how that may impact health. I think it likely that eating lots of fermented foods would promote the growth of bacterial colonies that may somehow aid in digesting soy. Or it could be just that other compositions of gut microbes produce by-products like excess gas which causes the pain and bloating. These are just my ideas at the moment, but I would bet that the impact of fermented foods in general and fermented soy in particular on the gut microbiota will be researched in the near future. And I look forward to hearing those results.

Lola Rosewig February 27, 2013 at 12:33 pm

Also, by “traditional” forms of soy I meant soybeans, edamame, tempeh, miso, etc.

Angela March 3, 2013 at 7:04 pm

Ha – I, too, wondered about the fermented/unfermented and digestive system differences. Over the years, many people have warned me about eating unfermented soy (I looooove tofu!), but I haven’t found any convincing evidence as yet. Don’t know what’s the latest on the fermented/unfermented debate…

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