Help please! I need an UN-BIASED opinion---Is soy bad for you?

Question

I am a vegetarian-have been for about 11/2 years. It works fine, I never feel malnourished or anything. But recently I have been trying to be way more halth-concious-really make sure I am getting balanced nutrients in my diet. I am also trying to lose about 7 lbs. Recently, I started incorporating alot of soy products into my diet- soy milk, tofu. But I just read an article "Is soy bad for you?" It said that soy is known to mess w/ your hormone levels, something I have been observing lately,my mood swings are alot more unexpected, and my menstruation cycle is coming more frequently. The article also said that soy conatins toxins and antinutrients. Another thing it pointed out was that it can mess w/ your thyroid, which is maybe why I can't seem to lose weight (altho it has always been a little tough for me).
I am so worried now. I need protein in my diet, and meat scares me. I don't want to be working hard just to be messing myself up. There is bad in eveyrthing. Am I overreacting?

Answer 1

Women are usually alright with soy, but men should try to keep it under 25g a day. It does influence hormone levels, but not as much as it sounds like this article of yours says. Sounds like this was an article designed as a scare tactic for someone. Take eggs, for instance. One day they're horrible, artery clogging killers loaded with cholesterol, and the next they're the staple of modern cooking, and eating them reduces bad cholesterol and increases good. It all depends on who's writing the article and what they're trying to sell.

If you're really worried about it, check with a nutritionist or see your doctor to have your thyroid tested. However, a simpler solution might be to do your own test. Try eating as you normally would, including soy, for a week... then try another week where you eat everything you normally would but without the soy. If you feel better without the soy, don't use the soy anymore.

Above all, don't panic. By worrying so much, you're only going to make your body worse. Focus on the good stuff, think positively, and eat the foods you enjoy!

Answer 2

NO - soy is not bad for you...cultures that have trationally used soy products for thousands of years are generally healthier than say western cultures that did not traditionally eat them...and they do not show the problems associated with soy until they change to a more western diet...the problem is that many westerners think if a little is good, more is better...eat soy as part of a balanced diet...get organic, non-GMO soy and enjoy it - just not with every meal...

Answer 3

You know there are other ways to get protein, right? Not every vegetarian relies on soy. Plus a growing number of people are allergic to it.

I think it's probably like any food--you have too much of it and it'll cause problems. Plus, some people are more sensitive than others.

Check this as a starting place if you want to try going soy-free and see how it affects you: http://www.vegcooking.com/askVeganChef1.aspx?Category=Health%20and%20Well-Being
Also try doing a search for things like vegetarian "soy allergy" or "without soy" or "allergic to soy".

Answer 4

Soy is good for you. But you need to make sure its in moderation. If you need some sources of protein why not try some nuts and fish. If it really seems to be bothering you go to your doctor. He'll know for sure if your going through some sort of soy overload.

Good luck!

Answer 5

Wow, this is interesting. I am very in tune to my body also. You might be reacting to the article you read, my hubby calls me a hypochondriac and says I do. Try going no soy and see what happens. It's all I got for you, sorry. Have you talked to your health food grocer?

Answer 6

moderation is always key in everything you do

Answer 7

http://www.soyonlineservice.co.nz/

Answer 8

Is It Safe to Eat Soy?



By Virginia Messina, MPH, RD & Mark Messina, PhD



No doubt you've heard lots of good things about soyfoods. According to a health claim sanctioned by the FDA, they can help to fight heart disease. 1 They may also make your bones stronger. 2, 3 And the biggest news about soyfoods over the past decade has been that they contain cancer-fighting compounds. 4



But just as it seemed that things couldn't get any better for soy, articles began to pop up on the internet saying that the pro-soy stories are nothing more than hype--and that the real scoop on soy is not nearly as positive. In fact, the stories say, eating soy could endanger your health. These claims against soy include allegations that it raises cancer risk, and causes nutrient deficiencies, osteoporosis, thyroid problems, reproductive difficulties, and Alzheimer's Disease.



Making your way through the controversy can be confusing, especially since some of what the soy naysayers claim is based on some scientific data--although this doesn't mean that their conclusions are right. And it's true that some soy proponents may overstate the benefits of soy. Hopefully, we can tread a more even path here and convince you that, while soyfoods may not be the answer to all your problems, and while there certainly are a few unanswered questions, you can include soyfoods in a balanced and healthful vegan diet.



In making our way through this quagmire, it is important to recognize some important facts about scientific research. It's true that there have been studies showing negative effects associated with soy consumption. But it is a rare situation where every single study on a subject is in agreement. There are always a few that sit in direct contrast to the majority of the studies. So it is never a good idea to suggest broad conclusions or recommendations based on one or two studies. By picking and choosing individual studies carefully enough, you can prove just about anything you would like about nutrition. That's why health experts look at all the research and pay attention to the totality of the evidence, not just to a few studies. Many of the studies that have concluded that soy is unhealthful have used animals as subjects. Drawing conclusions about human health from animal research can be very misleading. For example, broccoli and other cruciferous vegetables contain a compound (called indole-3 carbinol) that is an anticarcinogen in humans. But in some other species, it causes cancer. 5 If we looked only at the results of the studies in those species, the FDA would no doubt ban broccoli and cabbage from grocery stores.



Even so, soyfoods are significant in the diets of many vegans and it is worth taking a look at some of the claims against them.



Soyfoods and Thyroid
Many foods contain goitrogens, compounds that interfere with thyroid function (and in extreme cases can cause an enlarged thyroid, called a goiter). Along with soyfoods, millet, cruciferous vegetables and other foods contain goitrogens. Generally, these foods cause problems only in areas where iodine intake is low since this mineral is important for thyroid function. The effects of iodine deficiency can be made worse if the diet is high in goitrogens.



Although a concern about soy and thyroid function may be news to many vegans, it has actually been a focus of research for more than 70 years. 6 Between 1951 and 1961, this research took on a special importance when about 10 cases of goiter were diagnosed in infants who had been fed infant formula made from soy flour. These old studies form some of the basis for arguments that soy is dangerous for infants. However, the situation for today's soy formula-fed infant is very different. Since the 1960's,soy-based infant formula has been made from soy protein isolate (which does not contain the goitrogen component; soy flour formulas did) and it is fortified with iodine. No cases of goiter have been diagnosed in infants fed this formula in the past 40 years.



Nor is there any evidence that consuming soy causes thyroid problems in healthy, well-nourished people who have adequate iodine in their diet. . 7-10 However, it is possible that eating a diet with generous amounts of soyfoods could be a problem for people whose iodine intake is marginal. And that might just include some vegans, since the main sources of iodine in western diets are fish and milk. But the appropriate response to this is not to limit healthful soyfoods; it's to get enough iodine. Vegetables have varying amounts of iodine depending on where they are grown. In some parts of the world--specifically northern Europe--vegans may have low intakes of iodine. Foods that can supply iodine to vegan diets are sea vegetables, although contents vary quite a bit. Fortified foods are also a good source. Iodized salt is about the most reliable source. Vegans should be sure that, when they season foods with salt, it is iodized. If this isn't a regular part of your diet, use an iodine supplement.



Conclusion: Soyfoods may contain goitrogenic compounds as do other foods. There is no evidence that eating soyfoods regularly causes thyroid problems in people who eat a balanced diet. Vegans should make an effort to include adequate sources of iodine in their diet.



Soyfoods and Cognitive Function
A study conducted in Hawaii called the Honolulu Heart Study came up with a surprising finding. The study looked at Japanese men residing in Hawaii and aimed to compare diet to risk of dementia. The researchers found that those men who ate tofu most frequently during their mid-40's to mid-60's showed the most signs of mental deterioration in their 70's to early 90's. 11 In this study of over 3000 men, intake of 26 foods, including tofu, was recorded between 1965 and 1967 and again in 1971 to 1974. Cognitive test performance was assessed between 1991 and 1993 and the researchers also looked at brain shrinkage through autopsy data of the men who died during the study. Tofu consumption of just two to four servings per week was associated with poorer test performance and more brain loss. Not only that, but the wives of men who ate tofu also showed more signs of dementia.



The study raised lots of questions. For one thing, how could this be when it is known that dementia rates are lower in Asian countries than in western countries and when Japanese lifestyle has actually been associated with better cognition in old age? Many have used this as an argument to show that the Hawaii study results must be wrong. But comparing rates of dementia across cultures doesn't really tell us much in this regard because there are too many differences between the lifestyle in Japan and the lifestyle in Europe and North America. And criteria for diagnosing dementia vary across cultures. To get the real story, we would need to compare frequent tofu consumers in Japan to people in Japan who don't eat tofu. And that study hasn't been done yet.



Furthermore, there is a possible biological explanation for the findings. Soybeans contain isoflavones, which are weak estrogens. They fall into the category of estrogen-like compounds known as SERMS--selective estrogen receptor modulators. 12 This means that they have estrogenic effects in some tissues and anti-estrogenic effects in others. Estrogen may have a positive effect on brain tissue but the researchers of the Hawaii study suggested that isoflavones may have antiestrogenic effects on the brain. Of course, we can't know this from the Hawaii study. This was an epidemiological study, so it doesn't show cause and effect. It merely shows that two things occur together. Since the researchers measured intake of only 27 foods and were not able to control for every single lifestyle factor, it is possible that tofu consumption is a marker for some other factor that affects cognitive function. This would make tofu an innocent bystander. Results of other studies suggest this is true.



Results of three clinical studies, only one of which has thus far been published in full manuscript form, suggest soy and isoflavones have beneficial effects on cognition.In the published study, young adult men and women who consumed a high soy diet for 10 weeks experienced significant improvements in short-term and long-term memory and in mental flexibility. 13 The other two studies which have been presented at scientific meetings, found that isoflavone supplements, when taken by postmenopausal women, improve cognitive function.Even with these findings, we really have very little information on how soyfoods consumption might affect cognitive function. It's important to note though that studies of Seventh-day Adventists, many of whom have consumed soyfoods all of their lives, suggest that this group experiences less dementia in old age than the general population. 14 This may reflect an overall healthier lifestyle or higher education (which is linked to better cognitive function in old age). We simply don't know.



We do know that there are ways to protect cognitive function as we age. Eating a diet high in antioxidants (which means a plant-based diet), engaging in regular exercise, and stimulating the brain through learning and problem-solving activities, all seem to be associated with better cognitive aging. 15-19



Conclusion. One study has suggested a link between tofu consumption and poorer cognitive function in old age, but this is an epidemiological study. Therefore it doesn't show cause and effect. It did not look at diet extensively enough to draw firm conclusions. And there are no other studies to support it and three clinical studies suggest soy and isoflavones have beneficial effects on cognition.At this point, there is no reason to believe that eating soyfoods is harmful to brain aging.



Soyfoods and Mineral Absorption
Critics of soyfoods say that soy is high in phytates which inhibit absorption of iron, zinc, and calcium. But the absorption of calcium from soyfoods is actually surprisingly good given the phytate content of those foods. 20, 21 Not only that, but a number of studies have shown that the isoflavones in soyfoods protect bone health. 2 and that soy protein when substituted for animal protein decreases urinary calcium excretion. 3 So getting calcium from soyfoods that are either naturally rich in this nutrient or are fortified with it, seems like a very good idea.



However, there is certainly some research showing that vegan women have low calcium intakes. Contrary to popular opinion, there is little evidence that vegans have better bone health than people eating other types of diets and there is some evidence that links their lower calcium intake with poorer bone health. While this is a potential problem, it has nothing to do with any shortcomings of soyfoods. And it is an easily resolved problem. Vegans simply need to make sure they meet recommendations for calcium (1,000 mg a day for adults age 19-50) either through natural food sources of this nutrient, fortified foods or supplements. It is also important to make sure that your diet is well-balanced with adequate protein and with adequate vitamin D. While too much protein may be detrimental to bones, so is too little. And, while it is possible to make adequate vitamin D through sun exposure, it isn't a sure thing in many parts of the world so supplements or fortified foods are a good idea.



But it is true that, all other things being equal, phytates inhibit the absorption of iron and zinc. Soybeans are rich in phytate and vegan diets are especially high in phytate. It is very well documented that vegetarians absorb iron less well than meat eaters and have lower stores of iron in their bodies. But the implications of this aren't clear. Vegetarians don't appear to be any more likely to actually develop iron deficiency. 22 And, because high levels of iron may raise risk for heart disease, it may be that having lower but adequate stores as vegetarians do is the ideal situation. 23



Soy protein also inhibits absorption of iron, making soyfoods a poor source of available iron even though they contain this nutrient. So the critics are correct that people should not depend very much on soyfoods to meet their iron needs. And it may also be that the protein in soy inhibits absorption of iron from other foods. But this is not a reason to avoid soy. Rather, vegans should make sure that their diets are rich in good sources of iron--grains, beans, dried fruits, nuts, seeds, and many vegetables--and they should also make sure they get adequate vitamin C at meals. Vitamin C boosts absorption of iron from many plant foods. However, it is not enough to have a diet high in vitamin C. If you take a vitamin C supplement in the morning or consume a couple glasses of orange juice between meals, this won't affect your iron absorption. The vitamin C must be consumed at the same time as the iron.



Zinc is also poorly absorbed from soyfoods. Vegans generally have a lower intake of zinc and lower absorption than meat eaters and probably than lacto-ovo vegetarians. It's a nutrient that deserves some attention in vegan diets. But again, avoiding soyfoods is not the way to ensure adequate amounts of bioavailable zinc. Rather, making sure that your diet is rich in zinc-rich foods--nuts, seeds, whole grains, and legumes--is important.



Conclusion: Soyfoods can be good sources of well-absorbed calcium whether they are natural sources of this mineral or are fortified with it. They may also provide other factors that help to improve bone health. Vegans should make sure their diets are adequate in calcium and vitamin D and are generally well-balanced with adequate protein. Iron deficiency does not appear to be a problem for vegans--at least no more so than for people eating other kinds of diets. But, given that it is a common world-wide deficiency, everyone should make sure they eat plenty of iron-rich foods and vegans should consume good sources of vitamin C at meals. Likewise, it is important to eat plenty of zinc-rich foods every day.



Soy and Breast Cancer
All of the popular discussion surrounding soy actually started out because of evidence suggesting that soy, likely because of the isoflavones, reduced breast cancer risk by inhibiting the effects of estrogen. 24 Some of the evidence for this comes from the observation that breast cancer rates are lower in Asian countries than among western women. However, many factors that differ among cultures might affect breast cancer risk. And it is interesting to note that, within Asian cultures, there is little epidemiological evidence that shows soy consumption is protective against breast cancer.



A few short term clinical studies have suggested that soy consumption has estrogenic effects in the breast tissue of young--that is, premenopausal--women. 25, 26 This would suggest a possible increased risk for cancer. The significance of these short term studies isn't clear however. For example, the drug tamoxifen, used to treat breast cancer, actually has estrogenic effects when used for the short term, but antiestrogenic effects over the long term.



There are also a number of other considerations. First, research in laboratories on breast cancer cells has shown that small doses of the soy isoflavone genistein cause cells to replicate whereas large doses inhibit cell growth. Furthermore, there is some evidence that eating soy early in life--especially during puberty--helps to protect girls from breast cancer later in life. 27, 28 This would help explain why Asian women--most of whom grow up on soyfoods--have lower rates of breast of cancer than even western vegetarians, who might not begin eating soy until adulthood.



Finally, soy isoflavones have a number of effects that are possibly protective against cancer and that have nothing to do with their estrogenic or antiestrogenic effects. For example, genistein may inhibit the growth of the blood vessels that support tumor growth and may also inhibit enzymes that promote cell growth. Soy may alter estrogen metabolism in a way that protects against cancer.Also, year-long studies have found that soy or isoflavones either have no harmful effect or favorably affect breast tissue density, which is an indicator of breast cancer risk. 29



For women who have already had breast cancer and whose cancer is estrogen positive (meaning it is stimulated by estrogen) it is difficult to know whether to recommend restricting soy. The anti-cancer effects of soy may outweigh any possible estrogenic effects of isoflavones.



Conclusion: At this time, there seems no reason for women who have had breast cancer to avoid moderate consumption of soy. And for women who have never had cancer, there seems no reason to restrict soy.



Soy Intake and Reproduction
Scientists became aware of a potential link between isoflavone consumption and reproductive problems because of breeding problems among female sheep that grazed on a particular type of isoflavone-rich clover in Australia. 30 The amounts of isoflavones being ingested by these animals were extremely high compared to typical consumption of Asians. In addition, species vary in their response to biologically-active compounds and sheep are especially sensitive to isoflavones.



Although environmental estrogens, such as PCBs in fish, have been cited as possibly lowering sperm count and possibly interfering with fertility, 31 a recently published study showed that consumption of 40 mg of isoflavones per day had no effect on male reproductive function parameters. 32 And while one study has shown that soy consumption delayed ovulation in women, it did not prevent ovulation and several other studies have not found this effect. 33 Finally, a recent study of adults aged 20 to 34 years who were enrolled in controlled feeding studies at the University of Iowa as infants, found no difference in a wide range of reproductive and physiological measures between those who were fed soy formula and those fed cow milk formula as infants. 34 There have also been no observed widespread reproductive problems in populations where regular soy consumption is the norm.



Conclusion: Although soy isoflavones have weak estrogen-like effects, there is no evidence of reproductive problems in those who eat these foods.



Should You Eat Soy?

Based on the bulk of the evidence soy appears to be perfectly safe for nearly all healthy individuals when it is consumed in reasonable amounts. We would say that a reasonable amount of soy is two to three servings per day. Women who have had estrogen-positive breast cancer may want to be somewhat more restrictive in their soy intake but, if they are already eating and enjoying soyfoods, there is not enough evidence of any harmful effects to suggest that they need to avoid all soy.



About the Authors

Virginia Messina, MPH, RD is an adjunct assistant professor at Loma Linda University and a consultant on vegetarian nutrition. Mark Messina, PhD is an adjunct associate professor at Loma Linda University and an expert on soy and chronic disease. He is a consultant for numerous health professional organizations and for the soy industry.



Notes

1. Food and Drug Administration. Food labeling, health claims, soy protein, and coronary heart disease. Fed Reg 1999; 57:699-733.

2. Arjmandi BH, Smith BJ. Soy isoflavones' osteoprotective role in postmenopausal women: mechanism of action. J Nutr Biochem 2002; 13:130-137.

3. Breslau NA, Brinkley L, Hill KD, Pak CY. Relationship of animal protein-rich diet to kidney stone formation and calcium metabolism. J Clin Endocrinol Metab 1988; 66:140-6.

4. Messina M, Barnes S. The role of soy products in reducing risk of cancer. J Natl Cancer Inst 1991; 83:541-6.

5. Dashwood RH. Indole-3-carbinol: anticarcinogen or tumor promoter in brassica vegetables? Chem Biol Interact 1998; 110:1-5.

6. McCarrison R. The goitrogenic action of soya-bean and ground-nut. Ind J Med Res 1933; XXI:179-181.

7. Duncan AM, Underhill KE, Xu X, Lavalleur J, Phipps WR, Kurzer MS. Modest hormonal effects of soy isoflavones in postmenopausal women. J Clin Endocrinol Metab 1999; 84:3479-84.

8. Duncan AM, Merz BE, Xu X, Nagel TC, Phipps WR, Kurzer MS. Soy isoflavones exert modest hormonal effects in premenopausal women. J Clin Endocrinol Metab 1999; 84:192

9. Bruce B, Spiller GA, Holloway L. Soy isoflavones do not have an antithyroid effect in postmenopausal womem over 64 years of age. Faseb J 2000; 11:193 (abstract).

10. Ham JO, Chapman KM, Essex-Sorlie D, et al. Endocrinological response to soy protein and fiber in midly hypercholesterolemic men. Nutr Res 1993; 13:873-884.

11. White LR, Petrovitch H, Ross GW, et al. Brain aging and midlife tofu consumption. J Am Coll Nutr 2000; 19:242-55.

12. Brzezinski A, Debi A. Phytoestrogens: the "natural" selective estrogen receptor modulators? Eur J Obstet Gynecol Reprod Biol 1999; 85:47-51.

13. File SE, Jarrett N, Fluck E, Duffy R, Casey K, Wiseman H. Eating soya improves human memory. Psychopharmacology (Berl) 2001; 157:430-6.

14. Giem P, Beeson WL, Fraser GE. The incidence of dementia and intake of animal products: preliminary findings from the Adventist Health Study. Neuroepidemiology 1993; 12:28-36.

15. Engelhart MJ, Geerlings MI, Ruitenberg A, et al. Dietary intake of antioxidants and risk of Alzheimer disease. Jama 2002; 287:3223-9.

16. Foley DJ, White LR. Dietary intake of antioxidants and risk of Alzheimer disease: food for thought. Jama 2002; 287:3261-3.

17. Morris MC, Evans DA, Bienias JL, et al. Dietary intake of antioxidant nutrients and the risk of incident Alzheimer disease in a biracial community study. Jama 2002; 287:3230-7.

18. Ortega RM, Requejo AM, Lopez-Sobaler AM, et al. Cognitive function in elderly people is influenced by vitamin e status. J Nutr 2002; 132:2065-8.

19. Yaffe K, Barnes D, Nevitt M, Lui LY, Covinsky K. A prospective study of physical activity and cognitive decline in elderly women: women who walk. Arch Intern Med 2001; 161:1703-8.

20. Heaney RP, Weaver CM, Fitzsimmons ML. Soybean phytate content: effect on calcium absorption. Am J Clin Nutr 1991; 53:745-7.

21. Weaver CM, Plawecki KL. Dietary calcium: adequacy of a vegetarian diet. Am J Clin Nutr 1994; 59:1238S-1241S.

22. Messina VK, Burke KI. Position of the American Dietetic Association: vegetarian diets. J Am Diet Assoc 1997; 97:1317-21.

23. Ma J, Stampfer MJ. Body iron stores and coronary heart disease. Clin Chem 2002; 48:601-3.

24. Messina MJ, Persky V, Setchell KD, Barnes S. Soy intake and cancer risk: a review of the in vitro and in vivo data. Nutr Cancer 1994; 21:113-31.

25. Petrakis NL, Barnes S, King EB, et al. Stimulatory influence of soy protein isolate on breast secretion in pre- and postmenopausal women. Cancer Epidemiol Biomarkers Prev 1996; 5:785-94.

26. Hargreaves DF, Potten CS, Harding C, et al. Two-week dietary soy supplementation has an estrogenic effect on normal premenopausal breast. J Clin Endocrinol Metab 1999; 84:4017-24.

27. Lamartiniere CA, Zhao YX, Fritz WA. Genistein: mammary cancer chemoprevention, in vivo mechanisms of action, potential for toxicity and bioavailability in rats. J Women's Cancer 2000; 2:11-19.

28. Shu XO, Jin F, Dai Q, et al. Soyfood Intake during Adolescence and Subsequent Risk of Breast Cancer among Chinese Women. Cancer Epidemiol Biomarkers Prev 2001; 10:483-8.

29. Messina MJ, Loprinzi CL. Soy for breast cancer survivors: a critical review of the literature. J Nutr 2001; 131:3095S-108S.

30. Bennetts HW, Underwood EJ, Shier FL. A specific breeding problem of sheep on subterranean clover pastures in Western Australia. Aust J Agric Res 1946; 22:131-138.

31. Buck GM, Vena JE, Schisterman EF, et al. Parental consumption of contaminated sport fish from Lake Ontario and predicted fecundability. Epidemiology 2000; 11:388-93.

32. Mitchell JH, Cawood E, Kinniburgh D, Provan A, Collins AR, Irvine DS. Effect of a phytoestrogen food supplement on reproductive health in normal males. Clin Sci (Lond) 2001; 100:613-8.

33. Kurzer MS. Hormonal effects of soy in premenopausal women and men. J Nutr 2002; 132:570S-3S.

34. Strom BL, Schinnar R, Ziegler EE, et al. Exposure to soy-based formula in infancy and endocrinological and reproductive outcomes in young adulthood. Jama 2001; 286:807-14
Is It True What They Say About Soy?


Soybeans and their products, such as tofu (soybean curd) and soy milk, enjoy a reputation as very healthy foods, and they have risen in popularity in this country. Certain soy foods have earned the right to be labeled "heart-healthy." Yet not everybody is on board, judging by a recent spate of queries from our readers. "I won't allow soy in the house," one writes. Others ask if soy can fuel breast cancer, cause thyroid disease, or promote Alzheimer's. One unnerving report suggested that soy milk damages infant immune systems. A lot of people these days are afraid of soy.


Soybeans contain a complex mix of phytochemicals, including isoflavones. Some of these may act as estrogens or as anti-estrogens (the latter may block the effects of estrogens in the human body). Soy isoflavones may also act as antioxidants and have other beneficial effects on blood vessels and the heart. There's still a lot to learn about soy.


Soy and isoflavone supplements are in another category entirely. Since they concentrate the hormone-like substances in soy, they may well have a downside. Moreover, you have no guarantee as to what's in the supplements, and too little is known about them. We hope you will cross them off your list.


But what about soy foods? First, here are the potential problems and the conclusions so far:


Breast cancer: The high intake of soy foods in Asian countries has long been credited, at least by some researchers, for the lower rate of breast cancer among Asian women, compared with women in countries where little soy is consumed. But some confusion arises when you look at genistein, the main soy isoflavone and a plant estrogen. Does it protect against breast cancer or, on the other hand, promote the growth of existing cancer cells? Some studies have suggested the latter. Researchers at the Mayo Clinic recently reviewed all the evidence and concluded that soy has not been shown to fuel breast cancer cells. "If breast cancer patients enjoy soy products," they concluded, "it seems reason-able for them to continue to use them."
Whether soy actually protects against breast cancer is still unknown.


Soy milk and infants: A study published last year in the Proceedings of the National Academy of Sciences found that the highly concentrated phytoestrogens in soy formula might weaken the immune systems of babies. The formulas have more of these compounds than soy foods do. But researchers emphasized that this risk is largely theoretical. There's no evidence that soy formula is unsafe, or that infants drinking it have been harmed. Breast milk is still the first choice, however, followed by milk-based formulas. Only infants allergic to milk should drink soy formula.


Thyroid disease: One study suggested that soy protein supplements can interfere with the absorption of thyroid medications. Other research tentatively showed that soy foods may actually interfere with normal thyroid function, perhaps leading to goiter (swelling of the thyroid gland, located in the neck). But there's no risk of goiter in healthy people consuming soy who are not deficient in iodine. Strict vegetarians, who eat no iodine-rich fish or dairy products, might be at risk—and eating lots of soy might boost the risk. The answer is not to give up soy, but to increase iodine intake. One way is to use a small amount of iodized salt. And vary your diet as much as possible.


Alzheimer's disease: As we reported two years ago, a study of middle-aged Japanese-American men showed that those who ate at least two servings of tofu a week had a faster decline in mental ability as they aged and were more prone to Alzheimer's than men who ate no tofu. But this study raised more questions than it answered. No such effects have been seen in Japan, where life expectancy is high and tofu is a staple of the diet. Indeed, soy foods may actually protect the brain. The findings of this study are questionable and should not lead you to avoid tofu or other soy foods.


Kidney stones: If you've ever had calcium-oxalate kidney stones, the most common type, you should limit your intake of soy. Many soy foods are rich in oxalates and thus may promote the formation of such stones in those at risk, according to a study last year.


Now, a look at the positive side of soy foods. Not much is certain, but the outlook is promising:


Heart disease: Many researchers believe that the high intake of soy in Asian countries helps explain the lower incidence of heart disease there, and the FDA has okayed a "heart-healthy" claim for soy foods. Those that contain at least 6.25 grams (about one-quarter of an ounce) of soy protein per serving can claim on the label to reduce the risk of heart disease, when consumed as part of a healthy diet. Soy helps lower high blood cholesterol and may work in other ways to benefit blood vessels and the heart. So far, of all the potential health benefits of soy, this one has the most solid evidence.


Prostate cancer: In countries where soy is a dietary staple, men are less likely to develop prostate cancer. In animal studies, soy has slowed the growth of this cancer. This anti-cancer effect is still only hypothetical; more research is needed.


Menopausal symptoms: Soy supplements (capsules or pills) containing high levels of isoflavones, as well as soy foods with lower levels, have been promoted as effective remedies for menopausal symptoms such as hot flashes, irregular sleep patterns, and vaginal dryness. But no one knows how effective these plant hormones are—the evidence is contradictory—or whether they are safe. If isoflavone supplements act like hormones, they could pose some of the same dangers. Soy foods, on the other hand, may not have enough plant hormones to combat menopausal symptoms, but at least they aren't harmful. It can't hurt to try them, as part of a healthy diet.


Osteoporosis: According to research in Japan, women who consume a lot of soy tend to have greater bone mass. Japanese women also have a lower rate of hip fractures than American women, but that might be because of genetics or other factors. So far, there's reason to think that consuming soy is beneficial to bones, but long-term studies are still needed.




Keep in mind: Soy foods are well worth adding to your diet, since they may reduce the risk of heart disease. Other possible health benefits—not so well established—include protection against breast and prostate cancer and osteoporosis. Soy is not magical; it cannot fix up a poor diet. On the other hand, there is no convincing evidence that soy foods are harmful. People have been eating them for millennia, particularly in Asia. Remember that not all soy products are created equal—soy sauce, for instance, contains no soy protein. Even soy foods with a heart-healthy label may be high in salt, sugar, and calories. Be sure to read the labels.


UC Berkeley Wellness Letter, November 2002