Phytoestrogens are plant generated estrogen-like compounds that possess the ability to modulate hormone activity within the human body.
In the scientific and medical community, there is a great deal of controversy surrounding the intake of phytoestrogens. Despite decades of research, there is a rough consensus on whether phytoestrogens are beneficial or harmful to human health.
While most individuals equate phytoestrogens with soy, phytoestrogens exist rather ubiquitously through the plant world.
Foods or plant matter highest in phytoestrogens are1:
-Oilseeds (sunflower, canola, etc.)
-Soy and soy products
-Wheat and wheat products
-Processed meat products
There are four main classifications for dietary phytoestrogens2:
(The listing of examples in each category is not exhaustive)
-flavonols (quercetin, kaempferol, myricetin, fisetin, pachypodol, rhamnazin)
-flavones (apigenin, luteolin, tangeritin)
-flavanones (epicatechin, eriodictyol, hesperetin, homoeriodictyol, naringenin)
-isoflavonoids (glycitein, genistein, daidzein, formononetin, Biochanin A)
-prenylflavonoids (6‐prenylnaringenin, 6‐geranylnaringenin, 8‐prenylnaringenin and isoxanthohumol)
4) Stilbenes (polyphenols):
The most commonly consumed and researched forms of phytoestrogens in the western diet are1:
-Isoflavones (genistein, daidzein, glycitein, formononetin)
-Lignans (secoisolariciresinol, matairesinol, pinoresinol, lariciresinol)
Historically, we see the most considerable consumption of phytoestrogens in Asian countries. Intake of phytoestrogens through soy foods across Asia is found most frequently in edamame, tofu, fermented soy, bean curd, and soy sauces. Isoflavones in soy occur in glycoside form and break down into aglycone form during digestion. Bacterial hydrolysis to aglycone metabolites also takes place during the fermentation of soy.
While Asians consume less processed soy, Western consumption of soy tends towards more processing seen in bars, dietary supplements, food additives, and infant formulas.
Prominent research areas surrounding phytoestrogens include bone health, menopause, cancer, cardiovascular health, infant health, and cognitive function. Much of the data on soy remains inconclusive.
To determine why phytoestrogens generate such wide-ranging outcomes, we first need to understand the nature of their biological activity.
Phytoestrogens carry a structural similarity to 17-β-oestradiol (E2), which is considered the most potent of the three natural estrogens. By resembling E2, phytoestrogens act as competition for estrogen receptor site binding. Binding at the receptor results in modulation of receptor site expression and is considered the primary mode of action for phytoestrogens. When a phytoestrogen binds at an estrogen receptor site, it outcompetes the binding of endogenous estrogens. Phytoestrogens are considered weaker estrogens. The result of binding by phytoestrogens is deemed to be primarily anti(oestrogenic)3.
All humans have two primary estrogen receptors types: ERα and ERβ.
When phytoestrogens bind to ERα, we observe the proliferation of estrogen-dependent cancers, while the activation of ERβ can counteract ERα stimulation. Human tissues all contain various concentrations of each type of estrogen receptor throughout the body. Differential receptor expression suggests the hormonally regulated activity of the organ is unique at each location.
Research comparing 17-β-oestradiol (E2) vs. various phytoestrogens reveals most phytoestrogen compounds prefer binding to ERβ receptor sites.3
A study on the soy-derived isoflavone genistein reveals activation of ERβ at much lower concentrations before ERα activation occurs.4 A preference for ERβ is considered protective from an oncogenic standpoint.
New and emerging research is seeking to investigate the inter-individual variations which account for the lack of conclusive data on phytoestrogens.
Owing to research in the following areas, we now have a more accurate depiction of the influence of phytoestrogens on human physiology:
-The influence of phytoestrogens on genes which regulate cell proliferation and differentiation
-Cross-cultural variability in response to phytoestrogens
-Variation in estrogen receptor expression
-Gut microbiota and their impact on the metabolism of phytoestrogens
-Age-related epigenetic modifications in response to the consumption of phytoestrogens
-How differences in breast cancer types may respond to the intake of phytoestrogens
An ever-expanding body of research supports the contention that our lifestyle and environmental factors heavily influence our genome’s expression. In research involving phytoestrogens and cancer development, there is an added focus on studying cell-mediated interactions affecting apoptosis, cell proliferation and survival, inhibition of angiogenesis and metastasis, and antioxidant properties of phytoestrogens. Dangers attributed to soy intake stem from potential implications in the progression of cancer development.
All studies to date have been performed in vitro, in animal models, or gathered through epidemiological data.
The following is a summary of key findings on the proposed safety and biological activity of soy:
Despite extensive inquiry, the research on soy remains heavily convoluted. Individual variability also makes it difficult to predict the relationship between phytoestrogens and cancer development. The biological activity of phytoestrogens appear to be modulated by age, lifestyle, risk factors, diet, hormones, microbiome, pre-existing conditions, and type or quantity of phytoestrogen consumed.
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Naomi Sachs, B.Sc., A.C.H.N., PFT
Fully-certified since 2015, Naomi has been successfully coaching clients throughout North America and facilitating their self-growth in the nutrition and fitness realm. If you are feeling overwhelmed by the myriad of health strategies available, her services aim to introduce clarity and self-motivation.