Soy and Hormones

Estrogen and Testosterone

Excerpts from “Soyfoods Cooking for a Positive Menopause”

The phytoestrogens in soy are structurally similar to human estrogen, but very weak compared to the estrogens that the human body produces. They bind with estrogen receptors in the human body. Phytoestrogens are believed to protect against breast and prostate cancers, two hormone-dependent cancers. Isoflavones, found in soy, are only one type of phyto (or plant) hormone or sterol. There are many others available in a number of plant foods.

Soy foods have been studied exhaustively and it is now easy to figure how much isoflavone there is in a serving of one soy food or another. One tablespoon of flaxseed has about an equal portion of isoflavones to one portion of soy food. Wild yam is full of isoflavones and is used as a source for natural progesterone and estrogen therapy products, but it is not the same as the yam we buy in the grocery store.

Isoflavones resemble animal (or human, in this case) estrogens just enough to be accepted by cell estrogen receptors and bind weakly to the cell surface membrane. The estrogen receptors have been compared to “tiny switching stations”, “locks” or “docking stations” on the cells. Joanna Dwyer and colleagues at the New England Medical Center and Tufts University theorized in an article they wrote for The Journal of The American Dietetic Association (July 1994) that in pre-menopausal women the estrogen receptors are occupied and the weaker plant estrogens must compete for these sites. However, in postmenopausal women, whose self-produced estrogen declines about 60%, there is a far greater chance of the plant estrogens “docking” and this can increase the amount of estrogens available to her.

Perhaps the most important soybean estrogen in genistein. It is considered a powerful anticarcinogen and it is found in good supply in whole soybeans (including roasted soybeans or “soynuts”), textured soy protein, soy flour, soymilk, tofu and tofu products, and tempeh.

Daidzein, another soybean estrogen generously supplied by these soy foods, is now under intense study for its potential cancer-fighting and bone-building qualities. It, like genistein, is turned by intestinal bacteria into a substance that competes with human estrogen. Although other foods contain phytosterols, no other commonly consumed foods contain these two powerful phytoestrogens. And it has been proven in human studies that isoflavones in the diet are absorbed into the bloodstream– one study in which volunteers ate 40 grams of textured soy protein daily for just five days, the isoflavone levels in their urine (which indicates their presence in the bloodstream) increased as much as thousandfold in comparison to levels taken before the study.

In fact, in a 1993 study, women living in a controlled environment for two months had an average increase of two and a half days in the length of time between menstrual periods when they ate soy, which attests to the powerful effect phytoestrogens can have on a woman’s body.

This type of evidence has led a few scientists to wonder if eating large amounts of soy can lower fertility, but most authorities, including Mark Messina, Ph.D., author of The Simple Soybean and Your Health, points out that Chinese and Japanese women have no trouble with fertility levels, despite daily high soy intake. Kenneth Setchell, Ph.D., professor of Pediatrics at Children’s Hospital and Medical Center in Cincinnati says that, though soy lengthens the cycle, it does not prevent ovulation and there is still a normal menstrual cycle.


Boron, a trace element which is necessary for our health but which you need very little of, helps activate both vitamin D and estrogen. It is in good supply in plant foods, such as the soybean, but not in animal proteins. A study was done in 1986 of post-menopausal women between the ages of 48 and 82, led by Forrest Nielsen, Ph.D., director of the U.S, Department of Agriculture’s Agricultural research Center in Grand Forks, North Dakota. Boron supplementation markedly reduced urinary excretion of calcium and magnesium and also RAISED the level of and estrogen called estradiol-17 beta, a female hormone, and TESTOSTERONE (a precursor to estradiol-17 beta), a predominantly male hormone which women produce in smaller amounts, but which increases energy and libido. (Testosterone is now often prescribed in small amounts to postmenopausal women who have lost their sexual desire.) Boron supplementation is not recommended– it should be easy to ingest enough of this ultra-trace mineral on a plant-based diet containing lots of soy.

One of the factors that perked the interest of cancer researchers some years ago was the striking difference between mortality rates for breast cancer and prostate cancer in the West (North America and Europe) compared to Asian countries, such as China, Japan, the Republic of Korea, and Thailand. In the West, your chances of dying of breast or prostate cancer can be ten to twenty times higher than if you lived in one of these Asian countries! (Japan’s average daily soy intake is 29.5 g, whereas in the U. S. it is negligible. Japan’s breast cancer death rate is 6 per 100,000 people, and the U. S. rate is 22.4 per 100,000. Japan’s prostate cancer death rate is 3.5 per 100,000, and the U.S. rate is 15.7.)

Thanks to Bryanna Clark Grogan for the book excerpt.

Now, worried about hormones? Soy can help! A study published in the May 2000 issue of the Journal of the American College of Cardiology finds that phytoestrogens (natural chemicals found in many plants) provide women with many of the same benefits as hormone replacement therapy (HRT) without increasing the risk of breast or uterine cancers. In addition to treating hot flashes and other menopausal symptoms, research has shown that phytoestrogens may help prevent breast cancer, heart disease, and osteoporosis (a degenerative bone disease). Phytoestrogens are found in soybeans, flaxseeds, black cohosh, alfalfa spouts, and other plants.

The average amount of soy recommended for women to help protect against breast cancer is 35 grams per day-also the average amount Asian women consume per day. 60 grams is the maximum amount of soy used in clinical trials involving breast cancer patients. Products rich in phytoestrogens include soy milk, tofu, roasted soy nuts, soy protein powders, and tempeh. Not all soy products contain phytoestrogens (also called isoflavones).