Phytoestrogens are compounds found in various plant foods that can mimic the hormone estrogen in the body. Estrogen impacts nearly every major organ in the body, including the brain, bones, skin, gut and heart. Each of these organs contains estrogen receptors. Receptors function like a lock. When a key -- in this case, a hormone -- fits the lock, it will trigger a specific function in the body. While phytoestrogens act similarly to estrogen, the overall effect is less pronounced. Because of the wide role of estrogen, phytoestrogens in the diet have been linked to improved memory, cholesterol levels, bone development and cancer risk.
Types of Phytoestrogens
There are three types of phytoestrogens found in the diet: isoflavones found in legumes, lignans found in flaxseeds, and coumestans found in sprouts. Most scientific research has focused on isoflavones found in soy, especially their role in breast and ovarian cancers. It is important to note that phytoestrogen components can be isolated from the whole food and are used as fillers in processed foods or supplements. There may be a difference in health benefits based on where the phytoestrogens originate.
Health Benefits
The Shanghai Women's Health Study linked soy intake to decreased risk of breast cancer in perimenopausal women. Interestingly, the same benefit was not seen in postmenopausal women, indicating a potential impact of age on absorption or use of soy. Some evidence also suggests that soy intake may be protective against prostate cancer, male-pattern baldness and acne. Soy appears to inhibit the active, more potent form of testosterone from binding to receptors responsible for these processes. A study analyzing memory found that a 60 mg per day supplement of soy improved cognition in perimenopausal women, but a follow-up study involving postmenopausal women found no effect. Isoflavones and lignans may protect against heart disease by decreasing unhealthy LDL levels.
Concerns
While the benefits of phytoestrogens in the diet seem vast, there are inconsistent results in research. One study analyzing breast cancer cells found that they grew when exposed to soy isolates, a highly refined version of soy. The more concentrated the soy isolate, the more the cancer grew. However, when the same breast cancer cells were exposed to soy flour, no cancer growth was seen. This indicates that soy from whole foods may be protective against cancer, while processed versions may have the opposite effect.
Individual Variability
Bioavailability, or the amount of a nutrient the body is able to absorb, varies from person to person based on age, diet, gender and genetics. The bioavailability of phytoestrogens may vary depending on the source -- diet or supplement -- and also based on the person. Studies support the notion that benefits of phytoestrogens may be seen in specific populations during specific times of life. Asian populations appear to have decreased risk of breast cancer with increased intake of soy in the diet, yet other studies do not show the same effect in Europeans.
Controversy
The Women's Lifestyle and Health Cohort Study followed more than 47,000 women for 16 years in Sweden and found that high or low intakes of phytoestrogens were neither protective nor harmful. Another cancer study looking at phytoestrogens and incidence of prostate and colon cancer also did not find any links. This University of Cambridge study looked at the level of phytoestrogens in the blood and urine of subjects, which shows the amount actually absorbed by the body. This takes into account individual differences in absorption of phytoestrogens.
Considerations
Even though research has shown inconsistent results on the health benefits or concerns of eating phytoestrogens, it is important not to completely eliminate them from your diet. Consider eating less processed versions such as edamame since the null or harmful effects were seen exclusively with supplements containing soy isolates. Eat a variety of fruits and vegetables, whole grains and lean protein, and exercise for optimum health.
References
- "Micronutrients and Brain Health"; Lester Packer et al; 2010
- "Inflammapharmacology"; Health Benefits of Isoflavones in Functional Foods; M.C.Y. Wong, et al; Vol. 16, No. 5
- "Inflammapharmacology"; Phytoestrogens and Breast Cancer: A Complex Story; W.G. Helferich, et al; Vol. 15, No. 5
- "Biomarkers and Prevention"; Dietary Phytoestrogens and the Risk of Ovarian Cancer in Women's Lifestyle and Health Cohort Study; M. Hedelin et al; February 2011
- "Cancer Epidemiology Biomarkers and Prevention"; Lack of Prospective Associations Between Plasma and Urinary Phytoestrogens and Risk of Prostate and Colorectal Cancer in European Prospective into Cancer-Norfolk Study; Heather Hard et al; October 2008
