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- Linus Pauling Institute, Oregon State University: Soy Isoflavones
- Mayo Clinic: Soy
- Mayo Clinic: Soy Safety
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What Are the Dangers of Soy Isoflavones?
Soy, a member of the pea family, is native to the subtropical area of southeastern Asia. Soy contains fiber, protein, and isoflavones. According to the Mayo Clinic, soy isoflavones, sometimes called phytoestrogens, have estrogen-like effects in the body. Although soy has been a part of the diet in many countries for thousands of years, there are some dangers to its consumption.
Cancer
According to researchers at Oregon State University's Linus Pauling Institute, consuming large amounts of soy isoflavones may stimulate the growth of tumors in estrogen-sensitive breast cancer in women with a history of this type of cancer 1. Researchers recommend that, due to this possibility, these women do not consume large quantities of soy.
Large soy intake is also discouraged for women with a history of other cancers sensitive to hormones, such as ovarian and uterine cancer. There is also some concern about the effects of soy isoflavones on other conditions, such as endometriosis, that are sensitive to hormones.
- According to researchers at Oregon State University's Linus Pauling Institute, consuming large amounts of soy isoflavones may stimulate the growth of tumors in estrogen-sensitive breast cancer in women with a history of this type of cancer 1.
- There is also some concern about the effects of soy isoflavones on other conditions, such as endometriosis, that are sensitive to hormones.
Thyroid Function
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In animal and cell culture studies, soy isoflavones inhibit the activity of thyroid peroxidase, Oregon State University researchers note 1. Thyroid peroxidase is an enzyme that is necessary for the synthesis of thyroid hormone. Consuming adequate dietary iodine decreases this effect.
There is evidence that soy may also affect the levels of thyroid hormone in infants, the Mayo Clinic adds. Although rare, there have been cases of increased thyroid size that result in goiter, or enlarged neck.
- In animal and cell culture studies, soy isoflavones inhibit the activity of thyroid peroxidase, Oregon State University researchers note 1.
Infants
Because there is evidence that soy affect the levels of thyroid hormone in infants, iodine has been added to soy formula to eliminate this potential danger. Parents considering feeding their child soy formula should ask their pediatrician for a recommendation of a formula with the optimal amounts of vitamins and minerals.
Research on children during their first year has found that lower bone mineral density results when soy formula is used in place of cow's milk formula, the Mayo Clinic reports.
Infant girls fed soy-based formula report greater use of asthma or allergy drugs as adults than women who were fed cow's milk formula as infants, the Pauling Institute adds.
- Because there is evidence that soy affect the levels of thyroid hormone in infants, iodine has been added to soy formula to eliminate this potential danger.
- Research on children during their first year has found that lower bone mineral density results when soy formula is used in place of cow's milk formula, the Mayo Clinic reports.
Drug Interactions
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Some studies suggest that a high intake of soy isoflavones can interfere with the anti-tumor effects of cancer drugs, such as tamoxifen, researchers at Oregon State University's Linus Pauling Institute advise 1. Until more is known about the interactions between these types of drugs and soy, they recommend that these patients avoid isoflavone extracts or soy protein supplements.
Breast-cancer survivors taking anticoagulant medications, such as warfarin and aspirin, should also avoid high intakes of soy protein, as it may interfere with the efficacy of these medications.
Thyroid-replacement drugs doses are also affected by the ingestion of soy. The dose necessary for adequate thyroid function increases when consumption of soy products is high.
- Some studies suggest that a high intake of soy isoflavones can interfere with the anti-tumor effects of cancer drugs, such as tamoxifen, researchers at Oregon State University's Linus Pauling Institute advise 1.
- Until more is known about the interactions between these types of drugs and soy, they recommend that these patients avoid isoflavone extracts or soy protein supplements.
Other Dangers
Consumption of soy protein has been associated with symptoms of intestinal and stomach difficulties, such as:
- constipation
- bloating
- nausea,
- changes in stool quality
If you experience intestinal irritation from cow's milk, you may also experience this irritation with soy.
Related Articles
References
- Linus Pauling Institute, Oregon State University: Soy Isoflavones
- Ahsan M, Khurram Mallick AK. The Effect of Soy Isoflavones on the Menopause Rating Scale Scoring in Perimenopausal and Postmenopausal Women: A Pilot Study. J Clin Diagn Res. 2017 Sep;11(9):FC13–FC16. doi:10.7860/JCDR/2017/26034.10654
- Mason, P. Isoflavones. The Pharmaceutical Journal. 2001;266(7129):16-19.
- Yu J, Bi X, Yu B, Chen D. Isoflavones: Anti-Inflammatory Benefit and Possible Caveats. Nutrients. 2016;8(6):361. doi:10.3390/nu8060361
- Rietjens IMCM, Louisse J, Beekmann K. The potential health effects of dietary phytoestrogens. Br J Pharmacol. 2017 Jun;174(11):1263-1280. doi:10.1111/bph.13622
- Franco OH, Chowdhury R, Troup J, et al. Use of Plant-Based Therapies and Menopausal Symptoms: A Systematic Review and Meta-analysis. JAMA. 2016;315(23):2554-2563. doi:10.1001/jama.2016.8012
- Herbs and Phytoestrogens. National Women’s Health Network. Published 2015.
- Soy. Drugs.com. Updated January 9, 2018.
- Esch H, Lehmann L. Learn More About Isoflavones. Science Direct. Published 2016.
- Franco OH, Chowdhury R, Troup J, et al. Use of Plant-Based Therapies and Menopausal Symptoms: A Systematic Review and Meta-analysis. JAMA. 2016;315(23):2554-2563. doi:10.1001/jama.2016.8012
- Gardner C, Chatterjee L, Franke A. Effects of isoflavone supplements vs. soy foods on blood concentrations of genistein and daidzein in adults. The Journal of Nutritional Biochemistry. 2009 Mar; 20(3): 227–234. doi:10.1016/j.jnutbio.2008.02.008
- Mason P. Isoflavones. The Pharmaceutical Journal. 2001;266(7129):16-19.
- Rietjens IMCM, Louisse J, Beekmann K. The potential health effects of dietary phytoestrogens. Br J Pharmacol. 2017 Jun;174(11):1263-1280. doi:10.1111/bph.13622
- Vincent A, Fitzpatrick LA. Soy Isoflavones are they useful in menopause? Mayo Clinic Proceedings. 2000;(11):1174-84.
- Yu J, Bi X, Yu B, Chen D. Isoflavones: Anti-Inflammatory Benefit and Possible Caveats. Nutrients. 2016;8(6):361. doi:10.3390/nu8060361
- Zhang F, Haslam D, Terry M, et al. Dietary isoflavone intake and all-cause mortality in breast cancer survivors: The Breast Cancer Family Registry. Wiley Online Library. 2017. doi:10.1002/cncr.30615
Writer Bio
Based in northern Florida, Gail Morales has been writing and editing since 1997. Her articles have appeared in "UpDate," "The Messenger," "Dialog," "well-informed," "The Review," and on various websites. Morales received a B.S. degree in nursing, a B.A. degree in English/journalism, and a master's degree in education.