Isoflavones
Isoflavones are a group of plant-derived compounds classified as flavonoids, often referred to as phytoestrogens due to their structural similarity to estrogen hormones. They are primarily found in legumes, with soybeans being the richest source, containing key isoflavones like genistein and daidzein. Isoflavones are believed to confer various health benefits, particularly in relation to hormone-related cancers, including breast, prostate, and endometrial cancers. They work by binding to estrogen receptors in the body, specifically the beta receptors, which may help inhibit cancer growth.
Research into the health effects of isoflavones has evolved, with more recent long-term clinical studies suggesting potential protective benefits against breast and prostate cancer, particularly among populations with high soy consumption, such as Asians. However, findings have been mixed regarding their impact on cardiovascular health and menopausal symptoms. Some studies indicate that isoflavones might interfere with certain hormone therapies, so individuals undergoing such treatments should consult their healthcare provider before considering isoflavone supplementation. Overall, while the beneficial effects of isoflavones are increasingly recognized, further research is needed to fully understand their roles and efficacy in human health.
On this Page
Subject Terms
Isoflavones
ALSO KNOWN AS: Phytoestrogens
DEFINITION: Isoflavones are a subclass of plant chemicals known as flavonoids (also referred to as bioflavonoids in the media). The beneficial effects attributed to isoflavones have encouraged nutritional supplement manufacturers to refine and market isoflavones derived from soybeans. Although most of these purported benefits were once based only on epidemiological or laboratory animal studies, in the twenty-first century, more definitive conclusions with regard to human health are appearing with the results of long-term clinical trials.
Cancers treated or prevented:Breast, prostate, and endometrial cancers
Delivery routes: Oral by diet, pill, or capsule
How these compounds work: Isoflavones occur in foods bound to sugar in the form of glycosides. After ingestion, the glycosides are digested in the small intestine with the help of bacteria, releasing the active isoflavones. The isoflavones are absorbed and bound to plasma proteins for transport in the blood. There are two forms of estrogen receptors. Alpha receptors are predominantly found in reproductive tissue (uterus, breast, and ovaries), while beta receptors are predominant in other tissues. Isoflavones bind with the greatest affinity to beta receptors, while the hormone estrogen principally targets the alpha receptor. When isoflavones bind to estrogen receptors in the breast, endometrium, or prostate (in place of estrogen), they may help prevent cancer by inhibiting activation of the receptor and the resultant growth-signaling process.
Isoflavones are found naturally in legume plants. Soybeans contain the isoflavones genistein and daidzein, the most common active isoflavones in human foods. They are also known as phytoestrogens, since they are similar in structure to estrogen hormones produced in the human body and demonstrate weak estrogenic activity.
Many claims have been made regarding the beneficial actions of isoflavones. This may be attributable to the binding of isoflavones to beta receptors in various tissues to enhance the estrogen effect. One study evaluated the results of nineteen clinical trials with isoflavones and found that isoflavones had a negligible effect on cardiovascular risk factors. Likewise, isoflavones did not appear to be beneficial in reducing flushing or bone loss in postmenopausal women. Still, as the twenty-first century progressed and information on long-term clinical studies became available, the benefits of isoflavones became more apparent. A meta-analysis of eleven clinical studies done at Johns Hopkins Medicine showed daily consumption of isoflavones was responsible for a 26 percent reduction in breast cancer risk, especially in post-menopausal women. An additional studied appeared to confirm isoflavones can significantly reduce the prevalence of prostate cancer in men under certain conditions.
Epidemiological (population) studies indicate that Asians, who consume a traditional diet high in soy foods, have a much lower incidence of breast and prostate cancer than Western people. Studies have suggested that long-term exposure to high levels of estrogen may increase the risk of women developing breast or endometrial cancer. Although dietary consumption of isoflavones may provide protection for Asian women, it remains unclear whether the differences seen between them and Western women are attributable to high soy consumption during adolescence, lifetime consumption, or other factors.
Side effects: Some studies have indicated that the protective effect of hormone therapies for cancer, such as tamoxifen or other antiestrogenic drugs, may be abrogated by use of isoflavones; other study findings have disputed that idea. Those undergoing hormone therapies should consult their physician about the use of isoflavones.
Bibliography
Chabot, Guy G., et al. "Flavonoids in Cancer Prevention and Therapy: Chemistry, Pharmacology, Mechanisms of Action, and Perspectives for Cancer Drug Discovery." Alternative and Complementary Therapies for Cancer: Integrative Approaches and Discovery of Conventional Drugs. Ed. Moulay Alaoui-Jamali. New York: Springer, 2010.
“How to Prevent Prostate Cancer? - Prostate Cancer Prevention.” American Cancer Society, 22 Nov. 2023, www.cancer.org/cancer/types/prostate-cancer/causes-risks-prevention/prevention.html. Accessed 13 June 2024.
“Natural Compounds Derived from Soy and Other Plants Reduce Breast Cancer Recurrence and Improve Survival, Research Shows.” Johns Hopkins Medicine, 10 Jan. 2024, www.hopkinsmedicine.org/news/newsroom/news-releases/2024/01/natural-compounds-derived-from-soy-and-other-plants-reduce-breast-cancer-recurrence-and-improve-survival-research-shows. Accessed 13 June 2024.
Pejčić, Tomislav, et al. "The Role of Isoflavones in the Prevention of Breast Cancer and Prostate Cancer." Antioxidants, vol. 12, no. 2, 2023, p. 368, doi.org/10.3390/antiox12020368. Accessed 13 June 2024.
Simon, Stacy. “Soy and Cancer Risk: Our Expert's Advice.” American Cancer Society, 29 Apr. 2019, www.cancer.org/cancer/latest-news/soy-and-cancer-risk-our-experts-advice.html. Accessed 13 June 2024.
"Tips for Eating Healthier - Eating to Reduce Cancer Risk." American Cancer Society, 18 Oct. 2021, www.cancer.org/cancer/risk-prevention/diet-physical-activity/eat-healthy/add-fruits-and-veggies-to-your-diet.html. Accessed 13 June 2024.