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Sorting Out the Soy Story

Is it good or bad for you?

I have been trying to sort out the soy story for a very long time. Last week someone shared a link to a URL for the Weston Price Foundation that has pages and pages of information about the horrors of soy. One of these is titled "Teens Before Their Time" and talks about a rise in early maturity in American girls. They indict soy infant formula and cite a study done in 1986 called the Puerto Rico Premature Therlarche Study and state that "the most significant dietary association with premature sexual development was . . . soy infant formula."(Fallon 2002)


Later when quoting an individual who questioned the Puerto Rico findings, the Weston Price Foundation article asked "Why would [the author] leave out any reference to the Puerto Rico study in her review? Is it because Dupont, owner of Protein Technology Enterprises, is the leading manufacturer of soy protein isolate?" [The author at that time was employed at a hospital funded by Dupont.]


As most of you know, I am very committed to getting truthful balanced information. I was troubled by seeing a group that is priding itself on providing useful information make comments about the supposed agenda of a scientific article in this way. So I went and got the citation for the 1985 Puerto Rico study. Now, the original article actually says something very different from what the Weston Price Foundation implies. Yes, there were a whole group of girls who showed early sexual maturation. But in those children who were older than 2 when they sexually matured, there were "no significant associations" to any of the variables including soy formula. In those under 2, they found correlations with a maternal history of ovarian cysts, consumption of various products and soy formula. Even more astounding to me was the finding that the "statistical associations are probably not sufficient to explain the reported increase because in over 50% of the case subjects, there was no exposure to any of the risk factors for which statistical associations were found."(Freni-Titulaer, Cordero et al. 1986)


So the Weston Price Foundation quoted a finding out of context and made it sound like something totally different from what the study actually reported. They basically misrepresented the original data. I use this example to point to the information and misinformation with which the pro and con sides of the soy story have lined up. I have now read close to 500 scientific abstracts and articles on the soy story. Here is a very simplified summary of my own conclusions:


       Soy can have both very positive and negative effects.

       The type of soy products used can have very different effects.

       The amount of soy products used has significantly different effects.


In this discussion, I am going to lead you through a very simplified analysis of what I have found. It certainly is incomplete, but I hope it will give you a better understanding of some the issues and ways to make informed decisions.


The scientific interest in the role of soy in health was fueled by the observation that women in Asian countries (Japan, China and Indonesia) had significantly lower levels of breast cancer than women here.(Setchell 1998) These findings took a while to sort out and generated some very exciting dialogue in the scientific literature. (Morton, Arisaka et al. 2002)


Soy isoflavones are estrogenic. This means they are shaped like estrogen and they go and sit in the estrogen receptors. This can be good or bad depending on whether you want this effect or how much soy you have. During menopause, soy can 'soften' the impact of wildly fluctuating estrogen levels. (Setchell 2001)This is why it is now being marketed as a perfect 'all natural' solution, a great replacement for hormone replacement therapy.


There are some pretty clear benefits of soy in diet. A few of these are:


       Soy can have an impressive effect in limiting postmenopausal osteoporosis. This is one of the very positive estrogenic effects. (Scheiber, Liu et al. 2001), (Picherit, Bennetau-Pelissero et al. 2001), (Arjmandi, Birnbaum et al. 1998)


       Soy can improve vaginal health for post-menopausal women. It helps ward off what is known as vaginal atrophy that is a thinning of the vaginal wall that comes with aging. (Santen, Pinkerton et al. 2002), (Baird, Umbach et al. 1995)


       Soy contributes to lower cholesterol (this was shown with soy foods not as supplements). (Anderson, Johnstone et al. 1995)


       Soy is heart healthy because it relaxes coronary arteries, reduces inflammation, reduces blood lipids, homocysteine and blood pressure. (Setchell 2001)


       Soy seems to be chemo protective in certain breast cancers. This happens when the soy isoflavones go and sit in the estrogen sites and block the actual estrogen from signaling for the cancer cells to grow. This effect is true for those cancers that are made worse by higher levels of estrogen. (Pagliacci, Smacchia et al. 1994)


       Soy contains something called a protease inhibitor that can have powerful anticancer properties. Protease is an enzyme that is involved in making new cells. If you stop the process, you keep cancers from growing. Soy has been shown to have a very powerful effect on some cancers. (Kennedy 1998)


       Soy seems to have a particularly powerful effect on bladder cancer.(Su, Yeh et al. 2000)


       Soy protein intake is a very useful option for those with kidney disease because it is very low stress on the kidneys. (Anderson, Blake et al. 1998)


Of course, the very estrogenic effect that creates these desirable benefits can have a down side. Let's take a look at some of these:


The first of these, and perhaps that of the most questions comes with the use of soy for infants and children. That issue is so complex and important that I am going to write a separate piece about it. Let's take a look at some of the issues for adults.


       Soy protein at higher levels can disturb menstrual cycles in younger women (premenopausal) causing delayed menstruation and mid cycle surges of leutinizing hormones and suppressing FSH. Both can lead to the body getting confused about when and how to ovulate. (Cassidy, Bingham et al. 1995)


       One set of studies showed that adult cheetahs eating a soy diet became infertile and showed changes in their liver enzymes. There has been debate about whether these findings can be applied to humans but it does raise some questions that needs more study. (Setchell, Gosselin et al. 1987)


       Genistein, which is one of the isoflavones in soy, directly blocks the neurotransmitter GABAA. GABAA quiets the brain. It calms anxiety and panic. Drugs such as Valium, Librium, Halcyon, Ambien, Restoril and Klonipin activate GABAA. If you are prone to anxiety/panic or are taking any of these drugs, taking a soy product will not be a good idea. This effect does not occur with cooked products such as tofu. (Gumbmann, Spangler et al. 1986)


         Persons taking antidepressants called MAO inhibitors should avoid ALL soy products. (Shulman and Walker 1999)


       Episodes of nausea, feet edema and breast tenderness have been associated with taking genistein, one of the specific soy isoflavones.(Bloedon, Jeffcoat et al. 2002)


       Soy foods (not isoflavones) can inhibit iron absorption. This seems to be a function of the fiber found in the bean part of soy foods and can be overcome with the use of vitamin C. Wheat and oat bran have a similar effect. (Cook, Morck et al. 1981)


         Soy isoflavones can contribute to thyroid problems by inhibiting one of the steps in a long line of key actions that make for healthy thyroid function. This particular concern is often widely cited as the reason not to have soy. But it is important to note that this effect was only true in iodine deficient diets. Iodine comes from eating shellfish and iodized salt. (Divi, Chang et al. 1997)


       Genistein, a soy isoflavone, can create heart irregularity such as arthymia. (Paillart, Carlier et al. 1997), (Chiang, Chen et al. 1996)


       Tripsin inhibitors in uncooked soy used at high levels can create problems in the pancreas. There is some disagreement about the significance of these, but I would lend caution for people who have impaired pancreatic function such as diabetics.(Gumbmann, Spangler et al. 1986)


       There also seems to be a connection between soy and something called insulin like growth factor. This is a hormone that mimics insulin in the body. When our systems work well, a higher level of IGF means we need less insulin. IGF takes over some of insulin's job. This means we get less of the negative effects that come with high insulin levels. In one study, the level of IGF was increased on a "low" isoflavone diet in the study. (About 60 mg. per day for a 150 lb. person) and showed that higher levels of soy isoflavones decreased the level of IGF. (Maake, Yamamoto et al. 1997), (Wangen, Duncan et al. 2000), (Khalil, Lucas et al. 2002)


       Soymilk can reduce hair growth and the dimension of the hair shaft. It can also effect hair pigmentation. So drinking a lot of soymilk may create skinny, grey hair. (Seiberg, Liu et al. 2001)


Before the negative concerns spook you, go back and reread the positive things. As you can see, there are powerful effects on both sides of the equation. And, you can begin to see why all these conflicting claims would confuse any of us. After all this reading, my best sense is that some soy every day is a wonderful aid to health in many, many areas. This is particularly true if you are a woman who is approaching or in menopause. But too much soy creates real problems, including a contribution to weight gain by suppressing IGF and potentially contributing to hypothyroidism in iodine deficient people.


Many of us were seduced by the claims that soy is the all-powerful solution to hormone shifts. And we had a lot of it. Soy powder in shakes, soy lattes, soymilk as an alternative to dairy, soy cheese, edame at the sushi store, tofu quick and easy. We started getting a little tubbier; we felt that our metabolism wasn't quite right. We had tests and nothing showed but we knew something was operating. From what I have read, overuse of soy can certainly contribute to many of these subtle concerns we have had.


Now, does this mean we chuck it? Absolutely not. But I think it does mean we start paying attention to what kind and how much. I do think that using concentrated isoflavones is a not good idea at all. So what is the right amount? What is too much? Based on all that I have read, my current thinking is the right amount is one serving per day. One serving for a woman who is 150-200 pounds generally will mean between 25-40 mg of isoflavones that come from about 12-20 grams of soy product. Soy products generally have about 2 times the number of mg of isoflavones per gram of soy. The actual amount you eat should change according to your weight and age. As you get older and your estrogen levels diminish, you will want to have more. If you are a smaller person, you will have less. The idea is not to be scared or compulsive about the numbers, but simply to learn how much soy you are having. This is exactly the same process you used in learning to calculate the amount of protein you use. You get a sense of who you are and then plan your serving size accordingly.


This means if you use a soy protein powder, you should use a different liquid like oat or almond or cow milk. [Although I am thinking about the issue that soy fed cows and chickens may somehow be involved in this story.] (Brown and Setchell 2001)] If you want to use soymilk as your liquid, then choose a protein powder that does not contain soy.


If you plan on having tofu or tempeh for another meal, don't have a shake that day. If you are vegetarian, I would strongly encourage you to rethink the reliance on soy products as your primary protein source and look to other legume and nut sources as alternatives for your protein.


I also strongly advise you not to give your small children soymilk as an alternative to dairy. I will cover this in my next article on children and soy.


Let me make one final comment about the power of scientific findings. Many of the studies have what are called confounding variables which can affect the outcomes in a major way. Yes, the evidence from the breast cancer rate of Asian women is very compelling, but none of the studies make any reference to what I believe are 2 key factors in the incidence of breast cancers - the level of sugars and the proportion of Omega 3 to Omega 6 fatty acids. I think it is reasonable to assume that the traditional Asian diet is significantly higher in fish (Omega 3), lower in saturated fat (Omega 6) and lower in sugars than the typical American diet. So, I am not sure it is just the soy in the diet. I think the story is bigger than that.


But I hope this discussion has given you some way to make sense of all the claims. I will continue to have soy as a regular part of my diet, but plan on having way less than I have been.


Anderson, J. W., J. E. Blake, et al. (1998). "Effects of soy protein on renal function and proteinuria in patients with type 2 diabetes." Am J Clin Nutr 68(6 Suppl): 1347S-1353S.



Anderson, J. W., B. M. Johnstone, et al. (1995). "Meta-analysis of the effects of soy protein intake on serum lipids." N Engl J Med 333(5): 276-82.



Arjmandi, B. H., R. Birnbaum, et al. (1998). "Bone-sparing effect of soy protein in ovarian hormone-deficient rats is related to its isoflavone content." Am J Clin Nutr 68(6 Suppl): 1364S-1368S.



Baird, D. D., D. M. Umbach, et al. (1995). "Dietary intervention study to assess estrogenicity of dietary soy among postmenopausal women." J Clin Endocrinol Metab 80(5): 1685-90.



Bloedon, L. T., A. R. Jeffcoat, et al. (2002). "Safety and pharmacokinetics of purified soy isoflavones: single-dose administration to postmenopausal women." Am J Clin Nutr 76(5): 1126-37.


Brown, N. M. and K. D. Setchell (2001). "Animal models impacted by phytoestrogens in commercial chow: implications for pathways influenced by hormones." Lab Invest 81(5): 735-47.



Cassidy, A., S. Bingham, et al. (1995). "Biological effects of isoflavones in young women: importance of the chemical composition of soyabean products." Br J Nutr 74(4): 587-601.



Chiang, C. E., S. A. Chen, et al. (1996). "Genistein directly inhibits L-type calcium currents but potentiates cAMP-dependent chloride currents in cardiomyocytes." Biochem Biophys Res Commun 223(3): 598-603.



Cook, J. D., T. A. Morck, et al. (1981). "The inhibitory effect of soy products on nonheme iron absorption in man." Am J Clin Nutr 34(12): 2622-9.



Divi, R. L., H. C. Chang, et al. (1997). "Anti-thyroid isoflavones from soybean: isolation, characterization, and mechanisms of action." Biochem Pharmacol 54(10): 1087-96.



Fallon, S. a. E., M G (2002). Teens Before Their time.



Freni-Titulaer, L. W., J. F. Cordero, et al. (1986). "Premature thelarche in Puerto Rico. A search for environmental factors." Am J Dis Child 140(12): 1263-7.



Gumbmann, M. R., W. L. Spangler, et al. (1986). "Safety of trypsin inhibitors in the diet: effects on the rat pancreas of long-term feeding of soy flour and soy protein isolate." Adv Exp Med Biol 199: 33-79.



Kennedy, A. R. (1998). "The Bowman-Birk inhibitor from soybeans as an anticarcinogenic agent." Am J Clin Nutr 68(6 Suppl): 1406S-1412S.



Khalil, D. A., E. A. Lucas, et al. (2002). "Soy protein supplementation increases serum insulin-like growth factor-I in young and old men but does not affect markers of bone metabolism." J Nutr 132(9): 2605-8.



Maake, C., H. Yamamoto, et al. (1997). "The growth hormone dependent serine protease inhibitor, Spi 2.1 inhibits the des (1-3) insulin-like growth factor-I generating protease." Endocrinology 138(12): 5630-6.



Morton, M. S., O. Arisaka, et al. (2002). "Phytoestrogen concentrations in serum from Japanese men and women over forty years of age." J Nutr 132(10): 3168-71.



Pagliacci, M. C., M. Smacchia, et al. (1994). "Growth-inhibitory effects of the natural phyto-oestrogen genistein in MCF-7 human breast cancer cells." Eur J Cancer 30A(11): 1675-82.



Paillart, C., E. Carlier, et al. (1997). "Direct block of voltage-sensitive sodium channels by genistein, a tyrosine kinase inhibitor." J Pharmacol Exp Ther 280(2): 521-6.



Picherit, C., C. Bennetau-Pelissero, et al. (2001). "Soybean isoflavones dose-dependently reduce bone turnover but do not reverse established osteopenia in adult ovariectomized rats." J Nutr 131(3): 723-8.



Santen, R. J., J. V. Pinkerton, et al. (2002). "Treatment of urogenital atrophy with low-dose estradiol: preliminary results." Menopause 9(3): 179-87.



Scheiber, M. D., J. H. Liu, et al. (2001). "Dietary inclusion of whole soy foods results in significant reductions in clinical risk factors for osteoporosis and cardiovascular disease in normal postmenopausal women." Menopause 8(5): 384-92.



Seiberg, M., J. C. Liu, et al. (2001). "Soymilk reduces hair growth and hair follicle dimensions." Exp Dermatol 10(6): 405-13.



Setchell, K. D. (1998). "Phytoestrogens: the biochemistry, physiology, and implications for human health of soy isoflavones." Am J Clin Nutr 68(6 Suppl): 1333S-1346S.



Setchell, K. D. (2001). "Soy isoflavones--benefits and risks from nature's selective estrogen receptor modulators (SERMs)." J Am Coll Nutr 20(5 Suppl): 354S-362S; discussion 381S-383S.



Setchell, K. D., S. J. Gosselin, et al. (1987). "Dietary estrogens--a probable cause of infertility and liver disease in captive cheetahs." Gastroenterology 93(2): 225-33.



Shulman, K. I. and S. E. Walker (1999). "Refining the MAOI diet: tyramine content of pizzas and soy products." J Clin Psychiatry 60(3): 191-3.



Su, S. J., T. M. Yeh, et al. (2000). "The potential of soybean foods as a chemoprevention approach for human urinary tract cancer." Clin Cancer Res 6(1): 230-6.



Wangen, K. E., A. M. Duncan, et al. (2000). "Effects of soy isoflavones on markers of bone turnover in premenopausal and postmenopausal women." J Clin Endocrinol Metab 85(9): 3043-8.

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