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CancerQuest > Introduction to Patient Information > An Introduction to Cancer Treatments > Introduction to Complementary and Alternative Medicine (CAM) > CAM: Phytoestrogens (Soy)

CAM: Phytoestrogens (Soy)

Classified as:
Phytochemical, Phytoestrogens, Isoflavone

Types of Phytoestrogens
Isoflavones (e.g. genistein, daidzein, glycitein, formononetin) ⁽¹⁾

,
Structure of Genistein                                                          Structure of Daidzein

Lignans (e.g. secoisolariciresinol, matairesinol, pinoresinol, lariciresinol) ⁽¹⁾

Structure of a Lignan

Coumestan (e.g coumestrol) ⁽²⁾

Structure of Coumestan

Isoflavonoids

Structure of Isoflavonoids

Flavonoids (flavanols, flavanones, flavones, flavonols) ⁽²⁾

,
Structure of Flavonol                                                Structure of Flavone

Intro and Background:
The term phytoestrogen classifies a large group of compounds derived from plants and they are naturally found in many foods. Some of the major groups of phytoestrogens are isoflavones, lignans and coumestans. Isoflavones are most commonly found in soy (very rich in isoflavones), legumes, meat, cereals, nuts, fruits, and vegetables. Lignans are found in most plants with flaxseed registering the highest concentrations. ⁽¹⁾ Coumestans can be found in pinto beans, alfalfa sprouts, and vegetables. ⁽³⁾
Phytoestrogens have been found to exhibit antioxidant properties. ⁽⁴⁾ Because antioxidant activity is associated with the health and survival of cells, this discovery has led some to believe they may able to prevent and combat cancer in humans. ⁽⁵⁾ Another reason phytoestrogens are believed to be anticancer agents is the lower occurrence of prostate and breast cancer in Asian nations. In these countries, much more phytoestrogens from soy and vegetables are consumed than in Western countries. This intake, presumably, contributes to their low rate of these cancer types. ⁽⁶⁾

Please read our notice on CAM and chemoprevention methods

These compounds are also assumed to inhibit cancer growth because they have a structural similarity to steroid hormones like estrogen and testosterone. Estrogen is a known instigator of hormone responsive cancer types (i.e. breast, uterine, endometrial). The resemblance of phytoestrogens to estrogen allows them to bind to molecular receptors intended for this hormone, which may result in fewer cancer causing signals in cells. ⁽⁷⁾ Researchers believe that this class of compounds may also be involved in regulating apoptosis as well. ⁽⁴⁾ While, phytoestrogens might be good agents in the fight against cancer, they are also being studied for their possible ability to protect against cardiovascular disease, osteoporosis, and menopausal symptoms. ⁽¹⁾

Learn MORE about apoptosis

Scientific Research:
While older population studies from the early and mid-nineties hint that a diet higher in phytoestrogens may reduce hormone related cancers; recent studies have yielded conflicting results for the effectiveness of phytoestrogens against cancer. ⁽⁸⁾

One study has shown that high doses of a phytoestrogen from soy (genistein) can slow down the growth of mouse cancer cells in vitro. ⁽⁹⁾ Flaxseed oil, containing phytoestrogens, has also been shown to prevent estrogen related tumor cell growth in vitro and in mice. ⁽¹⁰⁾ On the other hand, phytoestrogens are also suspected to cause cancer and improper fetal development. ⁽¹¹⁾ Some European countries have even recommended maximum levels of soy intake per day. ⁽¹¹⁾ Other studies support the reason for using caution with phytoestrogens because they have shown that phytoestrogens increase breast cancer cell growth in vitro. ^{(8) (12)}

Currently, researchers are conducting several clinical trials designed to investigate the potential role of phytoestrogens in preventing cancer prevention and causation. ⁽⁸⁾ For information about ongoing clinical trials involving phytosestrogens, please visit our section on Finding Clinical Trials.

US Food and Drug Administration Approval
There is not enough evidence to support that phytoestrogens are effective in the fight against cancer and they have not been approved by the FDA for cancer treatment. ⁽¹³⁾

*It is important to keep in mind that many cancer treatments, including chemotherapy and radiation, work by generating free radicals in order to destroy cancer cells. If a cancer patient takes antioxidants while undergoing radiation or chemotherapy treatment, it is possible that these compounds may protect tumor cells from the desired free radicals. Doctors may recommend that patients undergoing these treatments avoid antioxidants so that the treatment is as effective as possible. ⁽¹⁴⁾

References for this page:

1. Thompson LU, Boucher BA, Liu Z, Cotterchio M, Kreiger N. Phytoestrogen content of foods consumed in Canada, including isoflavones, lignans, and coumestan. Nutr Cancer. (2006) 54(2):184-201 [PUBMED]
2. Yano S, Umeda D, Yamashita T, Ninomiya Y, Sumida M, Fujimura Y, Yamada K, Tachibana H. Dietary flavones suppresses IgE and Th2 cytokines in OVA-immunized BALB/c mice. Eur J Nutr. (2007) May 11 [PUBMED]
3. Horn-Ross PL, Barnes S, Lee M, Coward L, Mandel JE, Koo J, John EM, Smith M. Assessing phytoestrogen exposure in epidemiologic studies: development of a database (United States). Cancer Causes Control. (2000) 11(4):289-98 [PUBMED]
4. Cotterchio M, Boucher BA, Manno M, Gallinger S, Okey A, Harper P. Dietary phytoestrogen intake is associated with reduced colorectal cancer risk. J Nutr. (2006) 136(12): 3046-53. [PUBMED]
5. Kurzer MS, Xu X, Dietary Phytoestrogens. Annual Review of Nutrition (1997) 17:359-81 [PUBMED]
6. Sitori CR, Arnold A, Johnson SK. Phytoestrogens: End of Tale? Ann Med. 2005; 37(6): 423-38 [PUBMED]
7. Markiewicz L. Garey J, Adlercreutz H, Gurpide E, In Vitro Bioassay of Non-Steroidal Phytoestrogens. Journal of Steroid Biochemistry Molecular Biology (1993) 45(5): 299-405 [PUBMED]
8. Tempfer CB, Bentz EK, Leodolter S, Tscherne G, Reuss F, Cross HS, Huber JC. Phytoestrogens in clinical practice: a review of the literature. Fertil Steril. (2007) 87(6): 1243-9 [PUBMED]
9. Chen YC, Nagpal ML, Stocco DM, Lin T. Effects of Genistein, Resveratrol, and Quercetin on Steroidogenesis and Proliferation of MA-10 mouse Leydig Tumor Cells. Journal of Endocrinology. (2007) 192 (3); 527-37 [PUBMED]
10. Bergman Jungestrom M, Thompson LU, Dabrosin C. Flaxseed and its lignans inhibit estradiol-induced growth, angiogenesis, and secretion of vascular endothelial growth factor in human breast cancer xenografts in vivo. Clin Cancer Res. (2007) 13(3):1061-7. [PUBMED]
11. Sitori CR, Arnold A, Johnson SK. Phytoestrogens: End of Tale? Ann Med. 2005; 37(6): 423-38 [PUBMED]
12. Rice S. Whitehead SA. Phytoestrogens and Breast Cancer- Promoters or Protectors? Endocrin- Related Cancer. (2006) 13(4): 995-1015 [PUBMED]
13. US Food and Drug Adminstration website. Accessed 9/10/2010 [http://www.fda.gov/]
14. Borek C. Dietary antioxidants and human cancer. Integr Cancer Ther (2004). 3: 333-341. [PUBMED]