Mention “Silent Spring” and thoughts immediately turn to Rachel Carson’s epic in which she alerted readers to the risks of pesticides. But long before, way back in the 1940s, Australian sheep farmers experienced a silent spring of their own. The familiar baa baa of spring lambs was absent. Lambs were being born alright, but they were stillborn. What was causing the disaster? Actually it was the farmers themselves. Or at least the clover they had planted to feed their sheep.
It turned out that the clover was rich in a couple of natural estrogens, namely genistein and formononetin. As soon as clover was removed from the animals’ diet, the stillbirths stopped. Of course clover is not the only plant to produce estrogens with biological activity. There are a variety of plant derived estrogens, or “phytoestrogens.” The term estrogen comes from “estrus,” the willingness of a female to engage in mating activity and encompasses estradiol, estrone and estriol, three compounds that occur naturally in the human body. While plants do not contain these, they do contain a variety of structurally related compounds that can mimic the action of the naturally occurring human estrogens.
There are three main classes of phytoestrogens, namely isoflavonoids, coumestans and lignans. Coumestans are found in high concentrations in lima beans, clover, alfalfa sprouts, split peas. Beans and legumes are especially high in isoflavonoids, with soy beans and soy products being the richest source. Kidney, navy, pinto, red, small white and mung beans as well as chickpeas, split peas, peanuts and clover sprouts also contain estrogenic compounds. Lignans are found in flaxseeds as well as in sesame seeds, poppy seeds and sunflower seeds. Flours derived from wheat and rye also are sources of lignans as is rice. Fruits such as strawberries, peaches, pears, raisins, cherries, grapefruit, mandarin, kiwi, plums, oranges and apricots have lignans, with apricots having the highest amount. Vegetable sources of lignans include broccoli, cauliflower, brussel sprouts, cabbage, onions, garlic, leeks, French beans, red and green peppers, carrots, spinach, cucumbers, tomatoes and kale, with kale being the richest source of lignans. Even tomato paste, tofu and chocolate contain these compounds.
The effects of lignans in the diet are difficult to tease out given that they are found in foods together with numerous other potentiall biologically active compounds. It is interesting to note, however, that researchers such as Dr. Lilian Thompson of the University of Toronto have shown that giving breast cancer patients muffins containing twenty-five grams of ground flaxseeds a day resulted in reduced tumour growth.
And then there is meat. Estradiol and estrone are part of the mix of hormones commonly implanted into cattle to enhance growth and these contribute to our estrogen intake. And when meat is cooked a compound with the foreboding name 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine), abbreviated as PhIP is formed. It also has estrogenic properties and is suspected of being a carcinogen. Milk also contains a variety of estrogens. The recent increase of hormone-dependent cancers in Japan roughly parallels the increasing consumption of beef. During the past quarter century as beef consumption increased five –fold, hormone-dependent cancers have risen five-fold. More specifically, breast and ovarian cancer increased four-fold, endometrial eight-fold and prostate ten-fold. Of course such an association does not prove cause and effect but it does merit further investigation. The increased meat consumption is likely to be a bigger factor in the onset of disease than exposure to synthetic chemicals which have been widely blamed.
So what’s the point? We are awash in dietary estrogens, yet virtually every day brings some alarmist news about some synthetic chemical found in plastics, cleaning agents or cosmetics that is supposedly harming our health because of its estrogenic effect. This in spite of the fact that these are found in smaller amounts and have much weaker estrogenic potential than compounds found in plants, meat and dairy products. I’m not suggesting that there is no issue here. Just because there is an abundance of natural estrogens doesn’t mean that we should have no concern about adding to the load. But there is an undue emphasis on synthetic chemicals that may have estrogenic activity. I’m quite sure I’m getting more estrogenic compounds from my hummus than from the plastic container it comes in.