Everything about Phytoestrogens totally explained
Phytoestrogens sometimes called "dietary estrogens" are a diverse group of naturally occurring non steroidal plant compounds that because of their structural similarity with
estradiol (17β-estradiol), have the ability to cause
estrogenic or/and antiestrogenic effects.
Their name comes from
phyto = plant and
estrogen = estrus (period of fertility for female mammals) +
gen = to generate.
The similarities, at molecular level, of
estrogens and phytoestrogens, allow them to mildly mimic and sometimes act as antagonists to
estrogen but it was unknown if they could have any effect in human or animal metabolism. In the 1940s it was noticed for the first time that red clover (a phytoestrogens-rich plant) pastures had effects on the fertility of grazing sheep. Researchers are still exploring the
nutritional role of these substances in such diverse metabolic functions as the regulation of
cholesterol, and the maintaining of proper bone density post-
menopause. Evidence is accruing that phytoestrogens may have protective action against diverse health disorders such as
prostate,
breast,
bowel, and other
cancers,
cardiovascular disease,
brain function disorders,
menopausal symptoms and
osteoporosis
Phytoestrogens can't be considered as nutrients given that the lack of these in diet doesn't produce any characteristic deficiency syndrome nor do they participate in any essential biological function.
Ecology
These compounds in plants are an important part of their defense system mainly against fungi .
Phytoestrogens are considered archiestrogens (ancient, naturally occurring) and as dietary phytochemicals they're considered as co-evolutive with mammals. In human diet, phytoestrogens are not the only source of exogenous estrogens nor are they considered the largest source.
Xenoestrogens (novel, man-made), which are found as food preservants and ingredients, and also in cosmetics, plastics, insecticides as well as environmentally, have a consistent influence that's added to dietary phytoestrogens, making it difficult to clearly separate the action of these two kind of agents in studies done on populations.
Avian studies
The consumption of plants with unusual content of phytoestrogens under extraordinary conditions, have shown to decrease fertility in quail . Parrot food as available in nature has shown only weak estrogenic activity. Studies on screening methods for environmental estrogens present in manufactured supplementary food, with the purpose to enable reproduction of endangered species. have been researched .
Food sources
According to a study by Canadian researchers about the content of nine common phytoestrogens in a Western diet, foods with the highest relative phytoestrogen content were nuts and oilseeds, followed by soy products, cereals and breads,
legumes, meat products, and other processed foods that may contain soy, vegetables, fruits, alcoholic, and nonalcoholic beverages.
Flax seed and other oilseeds contained the highest total phytoestrogen content, followed by soy bean and
tofu. The highest concentrations of Isoflavones are found in soy bean and soy bean products (eg. tofu) followed by legumes, whereas lignans are the primary source of phytoestrogen found in nuts and oilseeds (for example flax) and also found in cereals, legumes, fruits and vegetables.
Phytoestrogen content varies in different foods, and may vary significantly within the same group of foods (for example soy beverages, tofu) depending on processing mechanisms and type of soy bean used. Legumes (in particular soybeans), whole grain cereals, and some seeds are high in phytoestrogen.
A more comprehensive list of foods known to contain phytoestrogens includes:
soy beans,
tofu,
tempeh,
soy beverages,
linseed (flax),
sesame seeds,
wheat,
berries,
oats,
barley,
dried
beans,
lentils,
rice,
alfalfa,
mung beans,
apples,
carrots,
wheat germ,
ricebran,
soy linseed bread,
ginseng,
bourbon and
beer
fennel and
anise
Health Risks and Benefits
In human beings, phytoestrogens are readily absorbed, circulate in plasma and are excreted in the urine. Metabolic influence is different from that of grazing animals due to the differences between ruminant versus monogastric digestive systems., there has been some unsubstantiated speculation that this similarity and the consumption of high quantities of phytoestrogens may result in hormonal imbalances. However, the scientific studies which have been done don't support these concerns. The main reason why the dietary consumption of phytoestrogens isn't considered a risk factor is that phytoestrogens don't appear to bioaccumulate.
Phytoestrogen in men
The use of phytoestrogens (as soy protein) in fast food meals and other processed foods as a low-cost substitute for meat products may lead to consumption of isoflavonoids by fast food eaters. A research team at the
Queen's University in
Belfast, in a review article, claims that such intake may lead to a slight decrease in male fertility, including a decrease in reproductive capability if isoflavones are taken in excess during childhood.
In theory, exposure to high levels of phytoestrogens in men could alter their hypothalamic-pituitary-gonadal axis. However, studies have shown that such a hormonal effect is minor. Isoflavones supplementation has no effect in sperm concentration, count or motility and show no changes in testicular or ejaculate volume. Researchers are studying if these mild effects may explain the protective effects of phytoestrogens in prostate cancer prevention.
Phytoestrogen in women
There are conflicting studies, and it's unclear if phytoestrogens have any effect on the cause or prevention of cancer in women.. While some epidemiological studies showed a protective effect against breast cancer,
in vitro studies concluded that women with current or past breast cancer should be aware of the risks of potential tumor growth when taking soy products, although the potential for tumor growth was found related only with small concentration of genistein and protective effects were found with larger concentrations of the same phytoestrogen. A 2006 review article stated the opinion that not enough information is available, and that even if isoflavones have mechanisms to inhibit tumor growth,
in vitro results justify the need to evaluate, at cellular level, the impact of isoflavones on breast tissue in women at high risk for breast cancer.
The generally accepted position on this topic is that phytoestrogens may be beneficial for healthy women and that women with known breast cancer should be aware of potential risks and consider avoiding consumption until more information is available.
Some reviews express the opinion that more research is needed to answer the question of what effect phytoestrogens may have on infants, but their authors didn't find any adverse effects. Multiple studies conclude there are no adverse effects in human growth, development, or reproduction as a result of the consumption of soy-based infant formula. One of these studies, published at the Journal of Nutrition
In some countries, phytoestrogenic plants have been used for centuries in the treatment of menstrual and menopausal problems as well as for fertility problems. The plants most used have been those that have later shown higher content of phytoestrogens for example
Pueraria mirifica, and its close relative,
kudzu,
Angelica, fennel and anise.
[Further Information]
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