This is a piece that I did a while back for Herbivore magazine about the ongoing soy controversy. Those who have done my 14-Day Cleansing Program often ask about "to soy or not to soy" and so I thought it would be helpful to post this article on the blog.
I recently read an article in Mothering magazine that had some really negative things to say about soy and soy formula. I also have seen some web sites on line that say soy could be harmful. Is there any truth to any of this? - P.A., Seattle, Washington
What in the world is up with soy these days? For the past twenty or thirty years soy has been the darling of the health food world. Who could possibly say anything bad about soy? Well, the Weston Price Foundation, the Gerson Institute, and now Kaayla Daniel, PhD, CCN, to name a few. Daniel's new book is titled "The Whole Soy Story: The Dark Side of America's Favorite Health Food." Thinking about the dark side of soy is like thinking about the dark side of Gandhi...or Mother Teresa. C'mon. It's crazy talk! Or is it?
The strange and unnatural things that are done to soy may be your last connection to pop food culture. Not Dogs and breakfast sausage are special to you, I know. And what the hell are you supposed to put in your coffee besides soymilk? Certainly not watery rice milk! Okay. Calm down and think this soy controversy through.
Let's review some reasons we turned to soy in the first place:
• It results in lower cholesterol levels than consuming meat, and as a result prob- ably contributes to reducing the risk of cardiovascular disease.
• It provides a high protein alternative for vegetarians and vegans.
• Several studies have supported the posi- tive effect on soy for menopausal symp- toms including hot flashes.
• Studies show soy may help to improve bone density in post-menopausal women.
• Soy consumption could facilitate weight loss because of its high protein, low fat content.
• Some studies have shown that soy is helpful in controlling blood sugar levels, again because it is a high protein, low carbohydrate food.
So, soy is irrefutably a superfood, right? Well, not so fast. For many a vegetarian or vegan, soy has become a major staple in the diet. Aren't there some days you look back and realize you have consumed it for breakfast, lunch and dinner...oh, and maybe it was even in the soy ice cream or vegan dessert that you had? The potential problems of soy are more likely to occur when the consumption is daily, in relatively large quantities, and over a long period of time.
So, now that we have seen the charming list of some soy virtues, let's take a look at the negative press that soy has been receiving recently. I have read much of this information on the internet and very little is actually referenced for source. I did some Medline searches on each of these topics and found some to be substantiated by a few studies, which are referenced here. Ultimately, you will have to make your own decision about whether soy belongs in your diet, and if so, how much.
Soy contains a chemical called phytic acid. This chemical, which is not removed in the cooking process, could reduce the absorption of some minerals. These include calcium, magnesium, copper, iron and zinc. There are several studies that seem to confirm reduced mineral absorption of iron and zinc. They don't indicate the amounts of soy necessary to do this, or exactly how much absorption it would affect.1, 2
Soy contains protease inhibitors. Proteases are enzymes that digest proteins. If soy does contain protease inhibitors, then it could possibly interfere with the proper digestion and assimilation of protein. Again, there is some research that confirms the existence of these enzyme inhibitors. What it doesn't indicate is how long these enzyme inhibitors stay active, or what the effects on health might ultimately be.3
To complicate matters further, an article in Circulation, the journal reporting on cardiovascular health, states that both phytic acid and the trypsin (a type of protease) inhibitor may be important mechanisms of action in lowering LDL cholesterol.4 This seems to be a stretch to believe, but it is referenced as having support. My first guess about why consuming soy helps to reduce the "bad" form of cholesterol is that it has as much to do with what you are not eating with as what you are eating. If you are consuming more soy, then it is likely you are substituting that for more saturated fat-containing foods. This change alone would help to lower serum cholesterol.
Soy contains phytoestrogens. While some studies indicate that it is the phytoestrogens that have the protective effect in cancers, other studies are less favorable. The problem may be that these phytoestrogens may bind to estrogen receptors in the body, causing negative effects, just as exogenous estrogens from synthetic hormone replacement therapy may cause harm. This may, then, actually increase the risk of breast or uterine cancer. The literature is mixed, with studies supporting both sides of the argument.
The American Cancer Society recommends that cancer survivors consume a moderate amount of soy. For example, some tofu in a stir-fry a few times a week may be harmless, but they should consider avoiding soy supplements in capsules. This also has to do with a study that concluded that the more processed forms of soy, like isoflavones, actually stimulated breast tumor growth in animals, while the consumption of soy did not.
Soy is a goitrogen. A goitrogen is a kind of food that suppresses the functioning of the thyroid gland.5, 6 The literature here is also mixed. The information comes from studies done on animals and it says that the studies reduced the function of the thyroid, but not enough to cause significant changes in blood values like TSH. TSH is a measure of thyroid function, and the major medical determinant as to whether a person is hypothyroid.
Soy also may be implicated in higher incidences of autoimmune disease in infants who consume soy formula.7 There is much controversy also about the safety of soy formula in general. One thing that emerges again and again is that the concentrate forms of soy (like isoflavones) have an estrogenic affect, which could potentially affect men or women. None of these ideas has had adequate research on humans.
A recent article in the Journal of Nutrition states that based on a review of the current information available about soy, that soy formula is safe. This article, which claims to review the "current evidence" available also seems to have been sponsored by a major manufacturer of soy formula.8 There's a surprise!
After reviewing the research in preparation for this article, I have to admit I am unclear as to what conclusion to draw. It seems ridiculous to imagine banning all soy from the diet, or to think about soy as being as harmful as fried food or barbecued meat. On the other hand, the "more is always better" mentality that we have in our culture doesn't seem to serve us when considering soy either. The answer, then, seems to be moderation. Here are some thoughts about the soy issue, based on some of the basic principles of natural medicine:
Soy is a highly processed food. It goes through quite a bit of heating. In the processing of tofu, the soybeans are heated to a high temperature and go through a solvent extraction process to remove the oils. This brings up another issue. In the course of processing, the naturally occurring essential fatty acids and carbohydrate portion of the soybean are removed. Soybeans themselves are also incredibly difficult to digest, probably because of the naturally occurring trypsin inhibitor. There are two types that can be digested: the black soy bean and the type which is still in the pod, also known as edamame (I love the tag line I saw recently shaping the image of this type of soy. It read, "Try edamame- the gay man's peanut." Very creative!)
The following is the process for making commercial soymilk. To remove the naturally occurring trypsin (protease inhibitor), the beans are first soaked in an alkaline solution, and then heated to 115 degrees. This denatures (destroys) the proteins. They are further processed to produce the pretty milk we all enjoy from those aseptic containers.
Soy is also one of the top food allergens. It ranks right up there with dairy, wheat, egg, peanuts, and citrus. It is typically included on any food allergy test panel that tests for the IgG immune system reaction in the blood. This reaction may be asymptomatic, causing chronic inflammation in the body. It may also cause symptoms like digestive distress. Some people eat soy for several years, and then notice that they are starting to react to it.
In fact, the top food allergens are those that people consume again and again, day in and day out. The body loves variety. The best way to protect yourself from the negative effects of any food would be to add variety to your diet. Read the labels! In the quest to find prepared palatable foods for vegetarians, I have seen many foods that contain some variation on soy, even when you wouldn't have expected to find any in the product.
Definitely avoid any soy product that does not specifically indicate that it is a non-GM (genetically modified) product. Food producers are not required to disclose if they use GM soy. However, most manufacturers want to let you know if they don't use GM soy, so look for that disclosure. Much of the soy now being produced in the United States is GM soy. Soy is in many products that the non-veggie population consumes as well. Remember Hamburger Helper? It's Texturized Vegetable Protein that helps to "extend the meat".
I would recommend considering moderate soy consumption. If you eat tofu or soy a few times per week, or one time per day, that seems reasonable. If you, however, have come to depend on soy as your main source of protein, then I suggest that you begin to consider some alternatives. I recommend raw nuts and seeds as at least one other alternative source of protein for vegans. These can be made into great milks, "mock tuna" or other faux dairy or meat dishes (e-mail Dr. Ariel at Herbivore for recipes). They contain protein as well as essential fatty acids. These EFA's have been removed from many soy derivatives as a result of the processing.
References:
1 Hurrell RF, Juillerat MA, Reddy MB, Lynch SR, Dassenko SA, Cook JD. "Soy protein, phytate, and iron absorption in humans." Am J Clin Nutr. 1992 Sep;56(3):573-8.
2 Egli I, Davidsson L, Zeder C, Walczyk T, Hurrell R. "Dephytinization of a complementary food based on wheat and soy increases zinc, but not copper, apparent absorption in adults." J Nutr. 2004 May;134(5):1077-80.
3 Miyagi Y, Shinjo S, Nishida R, Miyagi C, Takamatsu, Yamamoto T, Yamamoto S.," Trypsin inhibitor activity in commercial soybean products in Japan." J Nutr Sci Vitaminol 1997 Oct:43(5):575-80
4 "AHA Science Advisory: Soy protein and cardiovascular disease: A statement for healthcare professionals from the Nutrition Committee of the AHA." Circulation. 2000 Nov 14;102(20):2555-9.
5 Divi RL, Chang HC, Doerge DR. "Anti-thyroid isoflavones from soybean: isolation, characterization, and mechanisms of action." Biochem Pharmacol. 1997 Nov 15;54(10):1087-96.
6 Doerge DR, Sheehan DM. "Goitrogenic and estrogenic activity of soy isoflavones."
Environ Health Perspect. 2002 Jun;110 Suppl 3:349-53.
7 Fort P, Moses N, Fasano M, Goldberg T, Lifshitz F. "Breast and soy-formula feedings in early infancy and the prevalence of autoimmune thyroid disease in children."J American Coll Nutr, 1990 Apr; 9(2):164-7
8 Merritt RJ, Jenks BH. "Safety of soy-based infant formulas containing isoflavones: the clinical evidence."
J Nutr. 2004 May;134(5):1220S-1224S.
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