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Phytoestrogens

Possible health benefits

Possible health risks

An explanation

References

Many different plants produce compounds that may mimic or interact with estrogen hormones in animals. At least 20 compounds have been identified in at least 300 plants from more than 16 different plant families (1). Referred to as phytoestrogens, these compounds are weaker than natural estrogens and reside in herbs and seasonings (garlic, parsley), grains (soybeans, wheat, rice), vegetables (beans, carrots, potatoes), fruits (date, pomegranates, cherries, apples) and drink (coffee).

Most of us are exposed to many of these natural compounds through food (fruits, vegetables, meat). The two most studied groups of phytoestrogens are the lignans (products of intestinal microbial breakdown of compounds found in whole grains, fibers, flax seeds and many fruits and vegetables) and the isoflavones (found in soybeans and other legumes).

Because scientists have found phytoestrogens in human urine and blood samples, we know that these compounds can be absorbed into our bodies. In fact, phytoestrogens can have one of several fates after being eaten: they can be excreted; they can be absorbed into our bodies; or they can be broken down into other compounds that can also be potent phytoestrogens. Whatever their destiny, phytoestrogens differ remarkably from synthetic environmental estrogens in that they are easily broken down, are not stored in tissue and spend very little time in the body.

All in all, there are differing opinions about phytoestrogens' role in health. When consumed as part of an ordinary diet, phytoestrogens are probably safe and may even be beneficial. In fact, some studies on cancer incidences in different countries suggest that phytoestrogens may help protect against certain cancers (breast, uterus and prostate) in humans.

On the other hand, eating very high levels of some phytoestrogens may pose some health risks. Reproductive problems have been documented in laboratory animals, farm animals and wildlife that ate very high (up to 100% of their diet) amounts of phytoestrogen-rich plants.

Even though humans almost never eat an exclusive diet of phytoestrogen-rich foods (even vegetarians), those who consume uncooked soy or pop photoestrogen pills as a natural therapy may be exposing themselves to some health risks. Many natural compounds, especially hormones, can be potent and can have both good and bad health affects, depending on how much of it is in the body. These substances should always be used in moderation to avoid any unintentional health consequences.

Recent recearch (outlined in the article Phytoestrogens: Friends or foes?) may help to identify potential health benefits and shed some light on how plant compounds protect against certain diseases.

Phytoestrogens have been investigated as possible cancer preventatives and as treatments for menopause and osteoporosis (2). Laboratory animal experiments and comparisons of Asian and Western human populations suggest that diet has a large role in these types of health problems. One study found that Asian populations that eat large amounts of soy products - which contain high levels of phytoestrogens - have lower rates of hormone-dependent cancers (breast, endometrial) and a lower incidence of menopausal symptoms and osteoporsis than do Westerners, who don't traditionally eat these products. Asian immigrants to Western nations also increase their risks of these maladies as they Westernize their diets to include more protein and fat and reduce their fiber and soy (2).

Even short-term exposure to phytoestrogens may offer some long-term protection against some cancers, including breast, colon, prostate, liver and leukemia. According to some animal studies, phytoestrogens (mostly the soy-based compounds) eaten as part of an adult diet can protect against some types of cancer and may even inhibit tumor growth. Another animal study found that newborn rats injected with genistein (an isoflavone found in soy products) and then exposed to a cancer-causing agent later in life developed fewer tumors and waited longer to develop them than the nonexposed rats (2).

Gaining these possible benefits may involve more than just eating more soy products. Asians, for instance, have been eating these compounds for thousands of years and may have evolutionary adaptations that allow them to use phytoestrogens to their advantage. And, some plant and soy products contain other potential anti-cancer substances (such as protease inhibitors and antioxidants) that may also be responsible for some of the health benefits (3).

Evaluating health effects of phytoestrogens is difficult and depends on:

• the kind and dose (amount) of phytoestrogens eaten, and

• the age, gender and health of the person.

As for adverse health effects, the most likely risks associated with phytoestrogens deal with infertility and developmental problems (2). However, it is thought that very large amounts of dietary phytoestrogens would be needed to realize these risks.

Humans have used plants for medicinal and contraceptive purposes for eons. According to modern-day analyses, many of the plants historically noted for their ability to prevent pregnancies or cause abortions contain phytoestrogens and other hormonally-active substances. For instance, during the fourth century BC, Hippocrates noted that the wild carrot (now known as Queen Anne's lace) prevented pregnancies (4). Its seeds, we now know, contain a chemical that blocks progesterone, a hormone that is necessary for establishing and maintaining pregnancy.

More recent research shows that phytoestrogens can affect the fertility of animals that eat them. This is especially true when phytoestrogens represent the bulk of the diet, but this rarely the case for humans. Some examples from the animal world follow.

• Phytoestrogens in dry, summertime grasses reduced the number of offspring in wild populations of California quail (5) and deer mice (6).

• Australian sheep suffered from reproductive problems and infertility after grazing in pastures with the phytoestrogen-containing clover Trifolium subterraneum (7). Two phytoestrogen compounds, equol and coumestrol, were identified as the culprits.

• Rat pups, exposed to high doses of the plant estrogen coumestrol (found in sunflower seeds and oil and alfalfa spouts) through their mother's milk, suffered permanent reproductive problems: female pups when grown did not ovulate, and males had altered mounting behavior and fewer ejaculations (8).

• Neonatal and immature rats exposed to coumestrol experienced estrogen-related responses, such as premature estrous cycles. Coumestrol also interupted ovarian cycles in adult female rats (2).

• Newborn rats exposed to the phytoestrogen genistein (a compound found in soy products), experienced altered hormone secretions and the onset of puberty may have been delayed because female rats were exposed to the compound as fetuses (2).

Phytoestrogens behave like hormones, and like any hormone, too much or too little can alter hormone-dependent tissue functions. Taking too much of any hormone may not be good for a human or an animal. Similarily, too many phytoestrogens, at the wrong time, may have some adverse health effects. The studies listed above, which cannot be directly applied to humans, can help us to define what dietary levels are safe and clarify the possible reproductive and developmental risks associated with phytoestrogens.

Some scientists believe that plants make phytoestrogens as a defense mechanism to stop or limit predation by plant-eating animals (9, 10, 11). Instead of protecting themselves with thistles or thorns or tasting bad, these plants use chemicals that affect the predatory animal's fertility.

Although using estrogen-mimicking compounds for protection may sound far-fetched, it makes sense from an evolutionary stance. Many real-life examples support the theory that plants and animals change together, or co-evolve, over time.

The explanation goes something like this: to avoid predation, plants produce compounds (phytoestrogens) that limit a herbivores reproduction. Thus, the predator's population decreases and more plants prosper.

But remember, because of genetic differences, not all species or individuals of a given species will react to the phytoestrogens in the same way. While some herbivores may show fertility problems, others may acquire resistance - like some insects are resistant to pesticides and some bacteria that can survive antibiotics. Likewise, some humans may be more susceptible to the benefits and risks of phytoestrogens than others would be.

1. T. Colborn, D. Dumanoski and J.P. Myers. 1996. Our Stolen Future, p. 76. New York: Penguin Books.

2. Barrett, J. 1996. Phytoestrogens: Friends or foes? Environmental Health Perspectives 104:478-82.

3. Makela, S., R. Santti, L. Salo and J.A. McLachlan. 1995. Phytoestrogens are partial estrogen agonists in the adult male mouse. In Estrogens in the Environment (Proceedings Estrogens in the Environment, III: Global Health Implications). Environmental Health Perspectives 103(Supplement 7):123-127.

4. Riddle, J.M. 1994. Contraception and Abortion from the Ancient World to the Renaissance. Boston: Harvard University Press.

5. Leopold, A.S., M. Erwin, J. Oh and B. Browning. 1976. Phytoestrogens: Adverse effects on reproduction in California quail. Science 191:98-100.

6. Berger, P.J., E.H. Sanders, P.D. Gardner and N.C. Negus. 1977. Phenolic plant compounds functioning as reproductive inhibitors in Microtus montanus. Science 195:575-577.

7. Bennetts, H.W., E.J. Underwood and F.L.A. Sheir. 1946. A specific breeding problem of sheep on subterranean clover pastures in Western Australia. Australian Veterinary Journal 22:2-12.

8. Whitten, P., C. Lewis and F. Naftolin. 1993. A Phytoestrogen diet induces the premature anovulatory syndrome in lactationally exposed female rats. Biology of Reproduction 49:1117-21.

9. Ehrlich, P. and P.H. Raven. 1964. Butterflies and plants: A study of coevolution. Evolution 18:586-608.

10. Guillette, L.J. Jr. 1995. Endocrine disrupting environmental contaminants and developmental abnormalities in embryos. Human and Ecological Risk Assessment 1(2):25-36.

11. Hughes, C. 1988. Phytochemical mimicry of reproductive hormones and modulation of herbivore fertility by phytoestrogens. Environmental Health Perspectives 78:171-75.

EE vs hormones

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