Soybean

]

Role of soyfoods in disease prevention

Omega-3 fatty acids

Omega-3 fatty acids, for example, alpha-linolenic acid C18-3, all cis, 9,12,15 octadecatrienoic acid (where the omega-3 refers to carbon number 3 counting from the hydrocarbon tail whereas C-15 refers to carbon number 15 counting from the carboxyl acid head) are special fat components that benefit many body functions. However, the effects which are beneficial to health are associated mainly with the longer-chain, more unsaturated fatty acids eicosapentaenoic (20:5n-3, EPA) and docosahexaenoic acid (22:6n-3, DHA) found in fish oil and oily fish. For instance, EPA and DHA, inhibit blood clotting, while there is no evidence that alpha-linolenic acid (aLNA) can do this. Soybean oil is one of the few common vegetable oils that contains a significant amount of aLNA; others include canola, walnut, and flax. However, soybean oil does not contain EPA or DHA. Soybean oil does contain significantly greater amount of omega-6 fatty acids in the oil: 100g of soybean oil contains 7g of omega-3 fatty acids to 51g of omega-6: a ratio of 1:7. Flaxseed, in comparison, has an omega-3:omega-6 ratio of 3:1.

Isoflavones

Soybeans also contain the isoflavones genistein and daidzein, types of phytoestrogen, that are considered by some nutritionists and physicians to be useful in the prevention of cancer and by others to be carcinogenicFact|date=February 2008|date=February 2008 and endocrine disruptiveFact|Februarry 2008|date=February 2008. Soy's content of isoflavones are as much as 3 mg/g dry weight.Fact|date=February 2008|date=February 2008 Isoflavones are polyphenol compounds, produced primarily by beans and other legumes, including peanuts and chickpeas. Isoflavones are closely related to the antioxidant flavonoids found in other plants, vegetables and flowers. Isoflavones such as genistein and daidzein are found in only some plant families, because most plants do not have an enzyme, chalcone isomerase which converts a flavone precursor into an isoflavone.In contradiction to well known benefits of isoflavones, Genistein acts as an oxidant (stimulating nitrate synthesis), [British Journal of Nutrition. 89(5):607-616, May 2003.] as well as it blocks formation of new blood vessels (antiangiogenic effects). [UROLOGY official journal of the Société Internationale d'UrologieVolume 64, Issue 2, Pages 389-393 (August 2004)] Some studies show Genistein to act as inhibitor of the activity of substances in the body that regulate cell division and cell survival (growth factors).

Claims of cholesterol reduction

The dramatic increase in soyfood sales is largely credited to the Food and Drug Administration's (FDA) approval of health claims for soy in which studies are conflicting as to their cholesterol lowering ability.Cornell University Food and Brand Lab [http://www.foodpsychology.cornell.edu/research/soy/index.htm Article] ]

From 1992 to 2003, sales have experienced a 15% compound annual growth rate, increasing from $300 million to $3.9 billion over 11 years, as new soyfood categories have been introduced, soyfoods have been repositioned in the market place, thanks to a better emphasis on marketing nutrition.

In 1995, the "New England Journal of Medicine" (Vol. 333, No. 5) published a report from the University of Kentucky entitled, "Meta-Analysis of the Effects of Soy Protein Intake on Serum Lipids." It was financed by the PTI division of DuPont,"The Solae Co." [ [http://www.solae.com/ The Solae Company] ] St. Louis, Missouri, a soy producer and marketer. This meta-analysis concluded that soy protein is correlated with significant decreases in serum cholesterol, Low Density Lipoprotein LDL (bad cholesterol) and triglyceride concentrations. However, High Density Lipoprotein HDL(good cholesterol) did not increase by a significant amount. Soy phytoestrogens (isoflavones: genistein and daidzein) adsorbed onto the soy protein were suggested as the agent reducing serum cholesterol levels. On the basis of this research PTI, in 1998, filed a petition with FDA for a health claim that soy protein may reduce cholesterol and the risk of heart disease. It should be noted that only subjects with serum cholesterol of 250 mg/dl and higher showed any improvement in the study.

The FDA granted this health claim for soy: "25 grams of soy protein a day, as part of a diet low in saturated fat and cholesterol, may reduce the risk of heart disease." [cite web |last=Henkel |first=John |title=Soy:Health Claims for Soy Protein, Question About Other Components |url=http://www.fda.gov/fdac/features/2000/300_soy.html | publisher = Food and Drug Administration |accessmonthday=February 16 | accessyear=2008] One serving, (1 cup or 240 mL) of soy milk, for instance, contains 6 or 7 grams of soy protein. Solae resubmitted their original petition, asking for a more vague health claim, after their original was challenged and highly criticized. Solae also submitted a petition for a health claim that soy can help prevent cancer. They quickly withdrew the petition for lack of evidence and after more than 1,000 letters of protest were received. In February 18, 2008 Weston A. Price Foundation submitted a petition for removal of this health claim.cite web |url=http://westonaprice.org/soy/FDASoyHeartLetterFinal.pdf |title=Docket No. 2007N0-464 |accessdate=2008-03-08 |format= |work=]

In January, 2006 an American Heart Association review (in the journal "Circulation") of a decade long study of soy protein benefits casts doubt on the FDA allowed "Heart Healthy" claim for soy protein. This review of the literature compared soy protein and its component isoflavones with casein (isolated milk protein), wheat protein, and mixed animal proteins. [ [http://circ.ahajournals.org/cgi/content/full/113/7/1034#SEC2Soy Protein, Isoflavones, and Cardiovascular Health: An American Heart Association Science Advisory for Professionals From the Nutrition Committee -- Sacks et al. 113 (7): 1034 -- Circulation] ] The review panel also found that soy isoflavones have not been shown to reduce post menopause "hot flashes" in women and the efficacy and safety of isoflavones to help prevent cancers of the breast, uterus or prostate is in question. Thus, soy isoflavone supplements in food or pills is not recommended. Among the conclusions the authors state, "In contrast, soy products such as tofu, soy butter, soy nuts, or some soy burgers should be beneficial to cardiovascular and overall health because of their high content of polyunsaturated fats, fiber, vitamins, and minerals and low content of saturated fat. Using these and other soy foods to replace foods high in animal protein that contain saturated fat and cholesterol may confer benefits to cardiovascular health." [ [http://circ.ahajournals.org/cgi/content/full/113/7/1034#SEC5 Soy Protein, Isoflavones, and Cardiovascular Health: An American Heart Association Science Advisory for Professionals From the Nutrition Committee -- Sacks et al. 113 (7): 1034 -- Circulation] ] The original paper is in the journal "Circulation": January 17, 2006. [ [http://circ.ahajournals.org/cgi/content/abstract/CIRCULATIONAHA.106.171052v1?maxtoshow=&HITS=10&hits=10&RESULTFORMAT=&fulltext=soybeans%2Cfda&searchid=1138541151493_2869&FIRSTINDEX=0&search_url=http%3A%2F%2Fcirc.ahajournals.org%2Fcgi%2Fsearch&journalcode=circulationaha Soy Protein, Isoflavones, and Cardiovascular Health. An American Heart Association Science Advisory for Professionals From the Nutrition Committee -- Sacks et al., 10.1161/CIRCULATIONAHA.106.171052 -- Circulation] ]

Health risks

Phytoestrogen

Soybeans contain isoflavones called genistein and daidzein, which are one source of phytoestrogens in the human diet. Because most naturally occurring estrogenic substances show weak activity, normal consumption of foods that contain these phytoestrogens should not provide sufficient amounts to elicit a physiological response in humans. Fact|date=December 2007

Plant lignans associated with high fiber foods such as cereal brans and beans are the principal precursor to mammalian lignans which have an ability to bind to human estrogen sites. Soybeans are a significant source of mammalian lignan precursor secoisolariciresinol containing 13–273 µg/100 g dry weight. [cite journal |author=Adlercreutz H, Mazur W, Bartels P, "et al" |title=Phytoestrogens and prostate disease |journal=J. Nutr. |volume=130 |issue=3 |pages=658S–9S |year=2000 |pmid=10702603 |doi=] Another phytoestrogen in the human diet with estrogen activity is coumestans, which are found in beans, split-peas, with the best sources being alfalfa, clover, and soybean sprouts. Coumestrol, an isoflavone coumarin derivative is the only coumestan in foods. [cite journal |author=de Kleijn MJ, van der Schouw YT, Wilson PW, Grobbee DE, Jacques PF |title=Dietary intake of phytoestrogens is associated with a favorable metabolic cardiovascular risk profile in postmenopausal U.S.women: the Framingham study |journal=J. Nutr. |volume=132 |issue=2 |pages=276–82 |year=2002 |pmid=11823590 |doi=] [cite journal |author=Valsta LM, Kilkkinen A, Mazur W, "et al" |title=Phyto-oestrogen database of foods and average intake in Finland |journal=Br. J. Nutr. |volume=89 Suppl 1 |issue= |pages=S31–8 |year=2003 |pmid=12725654 |doi=10.1079/BJN2002794]

Soybeans and processed soy foods do not contain the highest "total phytoestrogen" content of foods. A study in which data were presented on an as-is (wet) basis per 100 g and per serving found that food groups from highest to lowest levels of total phytoestrogens per 100 g are nuts and oilseeds, soy products, cereals and breads, legumes, meat products, various processed foods that may contain soy, vegetables, and fruits. [ [http://www.leaonline.com/doi/abs/10.1207/s15327914nc5402_5 Lawrence Erlbaum Associates, Inc. - Nutrition and Cancer - 54(2):184 - Abstract ] ]

Women

A 2001 literature review suggested that women with current or past breast cancer should be aware of the risks of potential tumor growth when taking soy products, based on the effect of phytoestrogens to promote breast cancer cell growth in animals. [cite journal |author=de Lemos ML |title=Effects of soy phytoestrogens genistein and daidzein on breast cancer growth |journal=Ann Pharmacother |volume=35 |issue=9 |pages=1118–21 |year=2001 |pmid=11573864 |doi=]

A 2006 commentary reviewed the relationship with soy and breast cancer. They stated that soy may prevent breast cancer, but cautioned that the impact of isoflavones on breast tissue needs to be evaluated at the cellular level in women at high risk for breast cancer. [cite journal |author=Messina M, McCaskill-Stevens W, Lampe JW |title=Addressing the soy and breast cancer relationship: review, commentary, and workshop proceedings |journal=J. Natl. Cancer Inst. |volume=98 |issue=18 |pages=1275–84 |year=2006 |pmid=16985246 |doi=10.1093/jnci/djj356]

Men

Because of the phytoestrogen content, some studies, but not all, have suggested that there is an inverse correlation between soybean ingestion and testosterone in men. [cite journal |author=Dillingham BL, McVeigh BL, Lampe JW, Duncan AM |title=Soy protein isolates of varying isoflavone content exert minor effects on serum reproductive hormones in healthy young men |journal=J. Nutr. |volume=135 |issue=3 |pages=584–91 |year=2005 |pmid=15735098 |doi=] For this reason, they may protect against the development of prostate cancer. [cite journal |author=Heald CL, Ritchie MR, Bolton-Smith C, Morton MS, Alexander FE |title=Phyto-oestrogens and risk of prostate cancer in Scottish men |journal=Br. J. Nutr. |volume=98 |issue=2 |pages=388–96 |year=2007 |pmid=17403269 |doi=10.1017/S0007114507700703] A theoretical decrease in the risk of prostate cancer should, however, be weighed against the possible side-effects of decreased testosterone, which are still unclear. The popular fear that soybeans might cause reduced libido and even feminine characteristics in men has not been indicated by any study; the popularity of the notion seems to be based on the simplistic misapprehension that estrogen and testosterone have a simple, inverse relationship in sexual hormone systems and sex-related behaviour. Their interplay is very complicated and largely still unknown. [ [http://www.ncbi.nlm.nih.gov/pubmed/16775579?ordinalpos=1&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DiscoveryPanel.Pubmed_Discovery_RA&linkpos=5&log$=relatedarticles&dbfrom=pubmed Serum prostate-specific antigen but not testostero... [Eur J Clin Nutr. 2006 - PubMed Result ] ]

Studies published in July 2008 show that Soy products and, more specifically, the phytoestrogen they contain might lower a man's sperm count. [Jorge E. Chavarro, Thomas L. Toth, Sonita M. Sadio, and Russ Hauser. [http://humrep.oxfordjournals.org/cgi/content/short/den243v1 Soy food and isoflavone intake in relation to semen quality parameters among men from an infertility clinic] . "Human Reproduction", pp.1–7. July 23, 2008. [http://humrep.oxfordjournals.org/cgi/reprint/den243v1.pdf (pdf)] ]

Infant formula

There are some studies that state that phytoestrogen in soy can lead to alterations in the proliferation and migration of intestinal cells. The effects of these alterations are unknown. [cite journal |author=Chen AC, Donovan SM |title=Genistein at a concentration present in soy infant formula inhibits Caco-2BBe cell proliferation by causing G2/M cell cycle arrest |journal=J. Nutr. |volume=134 |issue=6 |pages=1303–8 |year=2004 |pmid=15173388 |doi=] However, some studies conclude there are no adverse effects in human growth, development, or reproduction as a result of the consumption of soy-based infant formula. [cite journal |author=Merritt RJ, Jenks BH |title=Safety of soy-based infant formulas containing isoflavones: the clinical evidence |journal=J. Nutr. |volume=134 |issue=5 |pages=1220S–1224S |year=2004 |pmid=15113975 |doi=] Other reviews agree, but state that more research is needed to answer the question of what effect phytoestrogens have on infants. [cite journal |author=Miniello VL, Moro GE, Tarantino M, Natile M, Granieri L, Armenio L |title=Soy-based formulas and phyto-oestrogens: a safety profile |journal=Acta Paediatr Suppl |volume=91 |issue=441 |pages=93–100 |year=2003 |pmid=14599051 |doi=] [cite journal |author=Chen A, Rogan WJ |title=Isoflavones in soy infant formula: a review of evidence for endocrine and other activity in infants |journal=Annu. Rev. Nutr. |volume=24 |issue= |pages=33–54 |year=2004 |pmid=15189112 |doi=10.1146/annurev.nutr.24.101603.064950] Soy formula has also been linked to autoimmune disorders of the thyroid gland. [cite journal |author=Fort P, Moses N, Fasano M, Goldberg T, Lifshitz F |title=Breast and soy-formula feedings in early infancy and the prevalence of autoimmune thyroid disease in children |journal=J Am Coll Nutr |volume=9 |issue=2 |pages=164–7 |year=1990 |pmid=2338464 |doi=]

Allergy

Allergy to soy is often said to be rather common, and the food is listed with other foods that commonly cause allergy, such as milk, eggs, peanuts, tree nuts, shellfish. However, a critical review of medical literature reveals surprisingly little solid information on the topic. The problem has been reported amongst younger children and the diagnosis of soy allergy is often based on symptoms reported by parents and/or results of skin tests or blood tests for allergy. Only a few reported studies have attempted to confirm allergy to soy by direct challenge with the food under controlled conditions. In these circumstances it is clear that skin/blood tests considerably overestimate the problem, as do parental reports. [cite journal | quotes = | last = Cantani | first = A | authorlink = | coauthor = Lucenti P| date = | year = 1997 | month = Aug | title = Natural history of soy allergy and/or intolerance in children, and clinical use of soy-protein formulas | journal = Pediatr Allergy Immunol | volume = 8 | issue = 2 | pages = 59-74 ] It is very difficult to give a reliable estimate of the true prevalence of soy allergy in the general population. To the extent that it does exist, soy allergy may cause cases of urticaria (hives) and angioedema (swelling), usually within minutes to two hours of ingestion of the food. In rare, severe cases true anaphylaxis may occur, a condition that is much more common with allergy to foods such as peanut and shellfish. The reason for the discrepancy is likely that soy proteins, the causative factor in allergy, are far less potent at triggering allergy symptoms than the proteins of peanut and shellfish. [cite journal | quotes = | last = Cordle | first = C T | authorlink = | date = | year = 2004 | month = May | title = Soy protein allergy: incidence and relative severity. | journal = Journal of Nutrition | volume = 134 | issue = 5 | pages = 1213S-1219S ] An allergy test that is positive demonstrates that the immune system has formed IgE antibodies to soy proteins. However, when soy is ingested proteins must evade digestion and be absorbed in a form capable of triggering allergy and also in sufficient quantities to reach a threshold to provoke actual symptoms. The low potency of soy proteins as allergens may help explain why allergy skin/blood tests suggest that soy allergy is common, yet few cases are confirmed when the food is eaten under observation.

Soy can also trigger symptoms via food intolerance, a situation where no immunologic (allergic) mechanism can be proven. One scenario is seen in very young infants who have vomiting and diarrhoea when fed soy-based formula. The symptoms resolve when the formula is withdrawn and recur when it is re-administered. That said, the intolerance resolves in most cases in a matter of months. Older infants can suffer a more severe disorder with vomiting, diarrhoea that may be bloody, anemia, weight loss and failure to thrive. The commonest cause of this unusual disorder is a sensitivity to cow's milk, but there is no doubt that soy formulas can also be the trigger. The precise mechanism is unclear and it could be immunologic, although not through the IgE-type antibodies that have the leading role in urticaria and anaphylaxis. Fortunately it is also self-limiting and will often disappear in the toddler years. [cite journal | quotes = | last = Sampson | first = H A | authorlink = | date = | year = 1999 | month = May | title = Food allergy. Part 1: Immunopathogenesis and clinical disorders | journal = Journal of Allergy and Clinical Immunology | volume = 103 | issue = 5 | pages = 717-728 ]

Promotion as health food

Soy consumption has been promoted by natural food companies and the soy industry's aggressive marketing campaign in various magazines, television ads and in health food markets. Research has been conducted examining the validity of the beneficial health claims with regard to the increase in consumption of soybeans which mimic hormonal activity.

A practice guideline published in the journal "Circulation" questions the efficacy and safety of soy isoflavones for preventing or treating cancer of the breast, endometrium, and prostate (although the same study also concludes that soy in some foods should be beneficial to cardiovascular and overall health) and does not recommend usage of isoflavone supplements in food or pills. [cite journal | quotes = | last = Sacks | first = FM | authorlink = | coauthors = Lichtenstein A, Van Horn L, et. al | date = | year = 2006 | month = Feb | title = Soy protein, isoflavones, and cardiovascular health: an American Heart Association Science Advisory for professionals from the Nutrition Committee. | journal = Circulation | volume = 113 | issue = 7 | pages = 1034–44 | doi = 10.1161/CIRCULATIONAHA.106.171052 | pmid = 16418439 | url = http://circ.ahajournals.org/cgi/content/short/113/7/1034 | format = | accessdate = 2006-10-21] A review of the available studies by the United States' Health and Human Services' Agency for Healthcare Research and Quality (AHRQ) found little evidence of substantial health improvements and no adverse effects, but also noted that there was no long-term safety data on estrogenic effects from soy consumption.cite web | publisher=Consumer Affairs | title=Study Casts Doubt On Soy's Health Benefits | date=2005-08-03 | url=http://www.consumeraffairs.com/news04/2005/soy_study.html ]

Brain

Estrogen helps protect and repair the brain during and after injury. [cite journal |author=Eberling JL, Wu C, Haan MN, Mungas D, Buonocore M, Jagust WJ |title=Preliminary evidence that estrogen protects against age-related hippocampal atrophy |journal=Neurobiol. Aging |volume=24 |issue=5 |pages=725–32 |year=2003 |pmid=12885580| doi = 10.1016/S0197-4580(02)00056-8] The mimicry of estrogen by the phytoestrogens in soy has introduced a controversy over whether such a replacement is harmful or helpful to the brain. Several studies have found soy to be harmful for rats. [cite journal |author=File SE, Hartley DE, Alom N, Rattray M |title=Soya phytoestrogens change cortical and hippocampal expression of BDNF mRNA in male rats |journal=Neurosci. Lett. |volume=338 |issue=2 |pages=135–8 |year=2003 |pmid=12566171| doi = 10.1016/S0304-3940(02)01391-5] Nevertheless the cited study was based on rats fed with concentrated phytoestrogens and not common soybeans. The common amounts of phytoestrogens in soy beans are not to be compared to concentrated estrogen.One study followed over 3000 Japanese men between 1965 and 1999, and that showed a positive correlation between brain atrophy and consumption of tofu.cite journal |author=White LR, Petrovitch H, Ross GW, "et al" |title=Brain aging and midlife tofu consumption |journal=J Am Coll Nutr |volume=19 |issue=2 |pages=242–55 |year=2000 |pmid=10763906 |doi= |url=http://www.jacn.org/cgi/pmidlookup?view=long&pmid=10763906]

Carcinogen

Raw soy flour is known to cause pancreatic cancer in rats.cite journal |author=Dethloff L, Barr B, Bestervelt L, "et al" |title=Gabapentin-induced mitogenic activity in rat pancreatic acinar cells |journal=Toxicol. Sci. |volume=55 |issue=1 |pages=52–9 |year=2000 |pmid=10788559| doi = 10.1093/toxsci/55.1.52] Whether this is also true in humans is unknown because no studies comparing cases of pancreatic cancer and soy intake in humans have yet been conducted, and the doses used to induce pancreatic cancer in rats are said to be larger than humans would normally consume. Heated soy flour may not be carcinogenic in rats.cite journal |author=Roebuck BD, Kaplita PV, Edwards BR, Praissman M |title=Effects of dietary fats and soybean protein on azaserine-induced pancreatic carcinogenesis and plasma cholecystokinin in the rat |journal=Cancer Res. |volume=47 |issue=5 |pages=1333–8 |year=1987 |pmid=3815341 |doi=] cite journal |author=Roebuck BD |title=Enhancement of pancreatic carcinogenesis by raw soy protein isolate: quantitative rat model and nutritional considerations |journal=Adv. Exp. Med. Biol. |volume=199 |issue= |pages=91–107 |year=1986 |pmid=3799291 |doi=] Existing cancer patients are being warned to avoid foods rich in soy because they can accelerate the growth of tumours. [ [www.news.com.au/dailytelegraph/story/0,22049,21054484-5001021,00.html Soy cancer warning] By Clair Weaver January 14, 2007 The Daily Telegraph]

Iron

A small-scale study published in 1995 concluded that "a vegetarian diet that is rich in soybean products and restricted in animal foods is limited in bioavailable iron and is not adequate for maintaining iron balance in men and women" [ [http://jn.nutrition.org/cgi/reprint/125/2/212 Shaw N, Chin C and Pan W, 1995. A Vegetarian Diet Rich in Soybean ProductsCompromises Iron Status in Young Students, "J Nutr" 125(2):212-219] ] .

References

While other studies shows that soybeans are high in phytic acid, which forms insoluble complexes with minerals such as iron, calcium, magnesium and especially zinc [Biosci Biotechnol Biochem. 2004 Jun;68(6):1379-81] ( i.e. blocks the uptake of essential minerals).

External links

Advocacy and nutritional information

* [http://www.soygrowers.com American Soybean Association]
* [http://www.foodpsychology.cornell.edu/research/soy/index.htm Cornell University Food and Brand Lab]
* [http://www.foodrevolution.org/what_about_soy.htm Evaluation of Anti-Soy Data and Anti-Soy Advocates]
* [http://www.guardian.co.uk/comment/story/0,,1839434,00.html Guardian - There's no risk to humans from soya]
* [http://www.cgiar.org/impact/research/soybean.html/ IITA has CGIAR global mandate for Soybean research for development]
* [http://www.iita.org/ International Institute of Tropical Agriculture]
* [http://72.32.142.180/soy_health.htm Soy information at Soyatech]
* [http://news.yahoo.com/s/hsn/20060127/hl_hsn/soyclaimashearthelperindispute Soy Heart healthy claims in dispute]
* [http://www.soyinfocenter.com Soyinfo Center - SoyaScan database and books]
* [http://www.soyconnection.com/ United Soybean Board]
* [http://www.bestsoybean.cn/ Shandong Shengfeng Bestsoybean industry Co.,Ltd.]

Critical

* [http://www.alternet.org/healthwellness/56087/ AlterNet: Health & Wellness: The Dark Side of Soy]
* [http://www.rheumatic.org/soy.htm Concerns Regarding Soybeans]
* [http://www.guardian.co.uk/food/Story/0,,1828158,00.html Guardian - Should we worry about soya in our food?]
* [http://www.hc-sc.gc.ca/fn-an/securit/allerg/allergen_soy-soja_e.html Health Canada: Soy - One of the nine most common food allergens]
* [http://www.aafa.org/display.cfm?id=9&sub=20&cont=522 Soy Allergy Information Page] Asthma and Allergy Foundation of America
* [http://www.soyonlineservice.co.nz/ Soy Online Service]