|The Soy Controversy|
|Wednesday, 26 May 2004 21:45|
This article summarizes a presentation given on May 25, 2001 at the 8th International Symposium of the Institute for Preventive Medicine in Vancouver, Canada.
Promotion of soy foods as a replacement for animal foods such as eggs, fish, meat, milk and poultry in the diets of men, women, children and infants in the US is being aggressively pursued by the government (the US Food and Drug Administration18), by individuals (authors Stephen Holt25,26 and Mark Messina34,35), and industry (American Soybean Association and Protein Technologies International, a division of DuPont). In addition, the pharmaceutical industry and major health food companies are promoting the fractionated phytoestrogens or isoflavones isolated from soy as a desirable treatment for peri- and postmenopausal women, as appropriate treatment for various hormone-based cancers, for hot flashes and to prevent osteoporosis.
At the same time, a number of scientists and writers have issued warnings53 about the adverse effects of soy, citing both the scientific literature dating back over 60 years as well as recently published studies. Most prominent among those raising concerns are Richard and Valerie James8,50 and toxicologist Mike Fitzpatrick16 in New Zealand; journalists Sue Dibb and Lynn McTaggart in Britain; and Sally Fallon and Mary Enig of the Weston A. Price Foundation in the US.15
This report will examine some of the claims made for soy, with emphasis on studies published within the last twelve years.
SOY USAGE IN ASIA
Soy proponents claim that soy is a staple in Asia. A "staple" is defined as a major commodity, one that provides a large portion of calories in the diet. Actually, overall consumption of soy in Asia is surprisingly low--it is not a staple like rice, fish or pork.
The famous Cornell study of diet in China, conducted by T. Colin Campbell, found that legume consumption ranged from 0 to 58 grams per day, with an average of about 13 grams.5,7 Assuming that two-thirds of this is from soybeans, this translates to about 9 grams (less than 2 teaspoons) of soy on average, with a high of about 2 tablespoons. [A 1975 book on nutrition published by the California Department of Health lists soy foods as minor sources of protein in Japanese and Chinese diets.41 Major sources of protein listed were meat including organ meats, poultry, fish and eggs.]
Soy is a condiment in Asian diets, not a staple. No one would call mustard a staple in the American diet even though it is a very typical foodstuff.
On October 26, 1999, the FDA authorized the use of a health claim for soy protein.18 The regulations stipulate that 25 grams of soy protein per day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease. Soy foods that contain at least 6.25 grams of soy protein per serving may make a Soy Health Claim. The rationale for this regulation is that Asians consume about 25 grams of soy protein per day and Asians have low rates of heart disease. Yet a study of Japanese men and women conducted in 1998, just one year before the FDA ruling, found that the average consumption of soy products was about 54 grams per day for women and 64 grams for men.36 The total amount of soy protein from these products was 7-8 grams.
Twenty-five grams of soy protein per day, the amount recommended by the FDA, provides about 75 mg or more of isoflavones, the estrogen-like compounds in soy. By contrast, the typical Japanese diet contains one-third as much. Total isoflavones in the 1998 dietary survey was about 25 mg.36 This is in line with a study published in 2000 giving about 28 mg isoflavones per day.37 A 1996 study found that consumption of isoflavones in Japan was considerably less, averaging about 10 mg per day.22
SOY USAGE IN ANIMAL DIETS
Pigs have a digestive system similar to humans. Dietary mixtures for pigs--which are carefully formulated to promote reproduction and growth--allow approximately 1 percent of the ration as soy in a diet based on grains and supplements.4 The Central Soya Company, Inc. website gives a range of 2.5 percent to 17.5 percent soy in the diet of pigs, citing a number of anti-nutritional components that "have been documented to cause gastrointestinal disturbance, intestinal damage, increased disease susceptibility and reduced performance in pigs."
In recent studies, rats fed the isoflavone genistein exhibited pathological changes in the colon23 and rats fed soy-based chow had reduced growth and an increase in gastrointestinal problems.40
SOY AND OSTEOPOROSIS
Many publications claim that soy foods can protect against osteoporosis. In one recent study, soy consumption seemed to attenuate bone loss from the spine in premenopausal women when measured by dual energy X-ray absorptiometry.1 However, in another study, soy did not prevent bone loss when measured at autopsy in female monkeys who had had their reproductive organs removed.9
SOY AND CORONARY HEART DISEASE
Claims that soy can prevent heart disease are based on the fact that soy consumption appears to lower so-called bad LDL and raise so-called good HDL.3,10,11,38,44 This hypothesis is dubious. Ravnskov and others have pointed out that serum levels of HDL and LDL are not good predictors of proneness to heart disease.46 [In fact, research indicates that high levels of HDL are an indication of thyroid problems.42 If this is so, higher levels of HDL after consumption of soy would tend to confirm soyâ€™s known antithyroid effects. Soyâ€™s effect on the thyroid gland "bounces all over the place," meaning that it can have repercussions on many different functions in the body.]
However, elevated levels of a substance called Lp(a) do provide an accurate marker for proneness to heart disease. In a recent study, consumption of soy was shown to raise levels of Lp(a).39
SOY AND FEMALE HORMONE REPLACEMENT
Soy promotion efforts have targeted women who are concerned about the side effects of hormone replacement therapy (HRT).12, 14, 33 Yet a study published in November 2000 concluded that "Current data are insufficient to draw definitive conclusions regarding the use of isoflavones as an alternative to estrogen for hormone replacement in postmenopausal women."52
In premenopausal women, significant changes in hormonal patterns and length of menstrual cycle were observed when 60 grams of a special soy protein containing 45 mg isoflavones was given daily for one month.6 The changes were similar to those observed in women taking tamoxifan and indicate that soy foods have the potential to disrupt the endocrine system.32 In another study, soy consumption increased sex hormone-binding globulin (SHBG) levels in postmenopausal women, which is further evidence of endocrine disruption.43
A study published March 2000 found that soy did not relieve hot flashes in breast cancer survivors.45
SOY CONSUMPTION AND
|Average Isoflavone Daily Intake||Isoflavone Intake per kg of Body Weight|
|Japan (1996 survey)22||10 mg||0.17 mg|
|Japan (1998 survey)36||25 mg||0.42 mg|
|Japan (2000 survey)37||28 mg||0.47 mg|
|In American women, causing hormonal changes after 1 month6||45 mg||0.75 mg|
|FDA recommended amount||75 mg||1.25 mg|
|In children receiving soy formula48||38 mg||6.25 mg|
- Alekel DL, St Germain A, Peterson CT, Hanson KB, Stewart JW, Toda T. Isoflavone-rich soy protein isolate attenuates bone loss in the lumbar spine of perimenopausal women. Am J Clin Nutr 2000;72:844-52.
- Anderson D, Dobrzyska MM, Bassaran N. Effect of various genotoxins and reproductive toxins in human lymphocytes and sperm in the Comet assay. Teratog Carcinog Mutagen 1997;17(1):29-43.
- Anthony MS, Clarkson TB, Williams JK. Effects of soy isoflavones on atherosclerosis: potential mechanisms. Am J Clin Nutr 1998;68:1390S-1393S.
- Bee G. Dietary Conjugated Linoleic Acids Alter Adipose Tissue and Milk Lipids of Pregnant and Lactating Sows. J Nutr 2000;130:2292-2298.
- Campbell TC. The Cornell-China-Oxford Project on Nutrition, Health and Environment. 1990.
- Cassidy A, Bingham S, Setchell KD. Biological effects of a diet of soy protein rich in isoflavones on the menstrual cycle of premenopausal women. Am J Clin Nutr 1994;60(3):333-340.
- Chen J, Campbell TC, Li J, Peto R. Diet, Lifestyle and Mortality in China. A study of the characteristics of 65 counties. Monograph, joint publication of Oxford University Press, Cornell University Press, China Peopleâ€™s Medical Publishing House. 1990.
- Chorazy PA, Himelhoch S, Hopwood NJ, Greger NG, Postellon DC. Persistent hypothyroidism in an infant receiving a soy formula: case report and review of the literature. Pediatrics 1995 Jul;96(1 Pt 1):148-50.
- Clarkson TB. Soy phytoestrogens: what will be their role in postmenopausal hormone replacement therapy? Menopause 2000 Mar-Apr;7(2):71-5.
- Clarkson TB, Anthony MS. Phytoestrogens and coronary heart disease. Baillieres Clin Endobrinol Metab 1998;12;589-604.
- Clarkson TB, Anthony MS, Morgan TM. Inhibition of postmenopausal atherosclerosis progression: A comparison of the effects of conjugated equine estrogens and soy phytoestrogens. J Clin Endocrinol Metab 2001;86:41-47.
- Clarkson TB, Anthony MS, Williams JK, Honore EK, Cline JM. The potential of soybean phytoestrogens for postmenopausal hormone replacement therapy. Proc Soc Exp Biol Med 1998;217:365-8.
- 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.
- Duncan AM, Hunderhill KE, Xu X, Lavalleur J, Phipps WR, Kurzer MS. Modest hormonal effects of soy isoflavones in postmenopausal women. J Clin Endocrinol Metab 1999 Oct;84(10):3479-84.
- Fallon S, Enig MG. Tragedy and Hype: The Third International Soy Symposium. Nexus Magazine 2000 April-May; 7(3).
- Fitzpatrick MG. Comments on Isoflavones in Soy-Based Infant Formulas. J Agric Food Chem 1998;46:3396-3397.
- Flynn KM, Ferguson SA, Delclos KB, Newbold RR. Effects of genistein exposure on sexually dimorphic behaviors in rats. Toxicol Sci 2000 Jun;55(2):311-319.
- Food and Drug Administration. Soy Health Claim. http://www.fda.gov/fdac/features/2000/300_soy.html
- Fort P, Lanes R, Dahlem S, Recker B, Weyman-Daum M, Pugliese M, Lifshitz F. Breast feeding and insulin-dependent diabetes mellitus in children. J Am Coll Nutr 1986;5(5):439-441.
- Fort P, Moses N, Fasano M, Goldberg T, Lifshitz F. Breast and soy-formula feedings in early infance and the prevalence of autoimmune thyroid disease in children. J Am Coll Nutr 1990;9:164-167.
- Freni-Titulaer LW, Cordero JF, Haddock L, Lebron G, Martinez R, Mills JL. Am J Dis Child 1986 Dec;140(12):1263-1267.
- Fukutake M, Takahashi M, Ishida K, Kawamura H, Sugimura T, Wakabayashi K. Quantification of genistein and genistin in soybeans and soybean products. Food Chem Toxicol 1996;34:457-461.
- Gee JM, Noteborn HP, Polley AC, Johnson IT. Increased induction of aberrant crypt foci by 1,2-dimethylhydrazine in rats fed diet containing purified genistein or genistein-rich soya protein. Carcinogenesis 2000;21:2255-2259.
- Hilakivi-Clarke L, Cho E, Clarke R. Maternal genistein exposure mimics the effects of estrogen on mammary gland development in female mouse offspring. Oncol Rep 1998 May-Jun;5(3):609-16.
- Holt, S. Soya for Health: The Definitive Medical Guide. Mary Ann Liebert Inc. 1996
- Holt, S. The Soy Revolution. Dell Health Publishing of Random House. 1999.
- Ikeda T, Nishikawa A, Imazawa T, Kimura S, Hirose M. Dramatic synergism between excess soybean intake and iodine deficiency on the development of rat thyroid hyperplasia. Carcinogenesis 2000 Apr;21(4):707-13.
- Irvine CH, Shand N, Fitzpatrick MG, Alexander SL. Daily intake and urinary excretion of genistein and daidzein by infants fed soy- or dairy-based infant formulas. Am J Clin Nutr 1998 Dec;68(6 Suppl):1462S-1465S.
- Ishizuki Y, Hirooka Y, Murata T, Togashi K. [The effects on the thyroid gland of soybeans administered experimentally in healthy subjects]. [Article in Japanese] Nippon Naibunpi Gakkai Zasshi. 1991 May 20;67(5):622-9.
- James V. Comments on Isoflavones in Soy-Based Infant Formulas. J Agric Food Chem 1998;46:3395-3395.
- Lebenthal E, Choi TS, Lee PC. The development of pancreatic function in premature infants after milk-based and soy-based formulas. Pediatr Res 1981 Sep;15(9):1240-1244.
- Makela S, Poutanen M Lehtimaki J Kostian ML, Santti R, Vihko R. Estogen-specific 17 beta-hydroxysteroid oxidoreductase type 1 (E.C.188.8.131.52) as a possible target for the action of phytoestrogens. Proc Soc Exp Biol Med 1995 Jan;208(1):51-9.
- Messina M. Soyfoods and soybean phyto-oestrogens (isoflavones) as possible alternatives to hormone replacement therapy (HRT). Eur J Cancer 2000 Sep;36 Suppl 4:71-2.
- Messina MJ. Legumes and soybeans: overview of their nutritional profiles and health effects. Am J Clin Nutr 1999 Sep;70(3 Suppl):439S-450S.
- Messina M. The Simple Soybean and Your Health. Avery Penguin Putnam, March 1994.
- Nagata C, Takatsuka N, Kurisu Y, Shimizu H. Decreased serum total cholesterol concentration is associated with high intake of soy products in Japanese men and women. J Nutr 1998 Feb;128(2):209-13.
- Nakamura Y, Tsuji S, Tonogai Y. Determination of the levels of isoflavonoids in soybeans and soy-derived foods and estimation of isoflavonoids in the Japanese daily intake. J AOAC Int 2000;83:635-650.
- Nilhausen K, Meinertz H. Variable lipemic response to dietary soy protein in healthy, normolipemic men. Am J Clin Nutr 1998;68:1380S-1384S.
- Nilhausen K, Meinertz H. Lipoprotein(a) and dietary proteins: casein lowers lipoprotein(a) concentrations as compared with soy protein. Am J Clin Nutr 1999;69:419-25.
- North K, Golding J. A maternal vegetarian diet in pregnancy is associated with hypospadias. The ALSPAC Study Team. Avon Longitudinal Study of Pregnancy and Childhood. BJU Int 2000 Jan;85(1):107-113.
- Nutrition during Pregnancy and Lactation. California Department of Health, 1975
- Olguin MC, Hisano N, Dâ€™Ottavio AE, Zingale MI, Gayol MC, Revelant G, Labourdette VB, Calderari SA. [Intestinal alterations and reduction of growth in prepuberal rats fed with soybean] [Article in Spanish] Medicina (B Aires) 1999;59:747-752.
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- Pino AM, Valladares LE, Palma MA,, Mancilla AM, Yanez M, Albala C. Dietary isoflavones affect sex hormone-binding globulin levels in postmenopausal women. J Clin Endocrinol Metab 2000;85:2797-2800.
- Potter SM.. Overview of proposed mechanisms for the hypocholesterolemic effect of soy. J Nutr 1995 Mar;125(3 Suppl):606S-611S.
- Quella SK, Loprinzi CL, Barton DL, Knost JA, Sloan JA, LaVasseur BI, Swan D, Krupp KR, Miller KD, Novotny PJ. Evaluation of soy phytoestrogens for the treatment of hot flashes in breast cancer survivors: A North Central Cancer Treatment Group Trial. J Clin Oncol 2000 Mar;18(5):1068-1074.
- Ravnskov, Uffe, The Cholesterol Myths: Exposing the Fallacy that Saturated Fat and Cholesterol Cause Heart Disease. NewTrends Publishing, Washington, DC. 2000.
- Santti R, Makela S, Strauss L, Korkman J, Kostian ML. Phytoestrogens: potential endocrine disruptors in males. Toxicocl Ind Health 1998 Jan-Apr;14(1-2):223-237.
- Setchell KD, Zimmer-Nechemiaas L, Cai J, Heubi JE. Exposure of infants to phyto-oestrogens from soy-based infant formula. Lancet 1997;3530(9070):23-27.
- Setchell KD, Zimmer-Nechemiaas L, Cai J, Heubi JE. Isoflavone content of infant formulas and the metabolic fate of these phytoestrogens in early life. Am J Clin Nutr 1998 Dec; 68(6 Suppl):1453S-1461S.
- Soy controversy information website: http://www.soyonlineservice.co.nz/.
- Strauss L, Makela S, Joshi S, Huhtaniemi I, Santti R. Genistein exerts estrogen-like effects in male mouse reproductive tract. Mol Cell Endocrinol 1998 Sep 25;144(1-2):83-93.
- Vincent A, Fitzpatrick LA. Soy isoflavones: are they useful in menopause? Mayo Clin Proc 2000;75:1174-84.
- Washington Post Health Section January 30, 2001 article: "You have to be soy careful: tofu and similar foods may be beneficial, but some experts fear that too much could be unsafe."
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