Do Estrogens In Soy Increase Prostate Cancer Risk?

At present, confusion and controversy surround the inclusion of soy in the diet of those men at risk for developing prostate cancer.


Research on soy and prostate cancer presents a conflicting picture.

A Japanese study published in Cancer Epidemiology Biomarkers & Prevention found a correlation between increased intake of soy isoflavones and decreased risk of localized prostate cancer.

The 20 year study of 8000 Japanese men in Hawaii found a direct correlation between tofu consumption and lower rates of prostate cancer. Those who consumed tofu once a week or less were three times as likely to get prostate cancer as those who ate it daily.

The same study found, however, that a high intake of these compounds correlated with more severe cases of advanced prostate cancer.

The benefits of soy

Countries that have a high intake of soy in their diet tend to have much lower rates of prostate cancer compared to  countries where soy intake is fairly low.

Plant chemicals known as isoflavones are thought to play a key role in soy’s amazing cancer-protecting qualities. One isoflavone in particular, genistein, has been found to be effective in slowing the progression of prostate cancer.

In a study conducted at the University of California in the US, scientists added genistein to a culture of human prostate cancer cells. It was found to spur the production of a gene called p21, which inhibits the manufacture of a protein that cancer cells need to grow, so causing the cancer cells to die off. Animal studies have confirmed that genistein can reduce the size of prostate cancer tumors.

How can soy benefit prostate cancer?

The protection against cancer may come from phyto-oestrogens in soy. Phyto-oestrogens are chemicals found in plant foods (phyto means ‘plant’).  They are similar to the female sex hormone oestrogen.  There are different types of phyto-oestrogens.  Some are found in soya bean products.  Others are found in the fiber of whole grains, fruit, vegetables and flax seed.  Milk may also contain phyto-oestrogens, but this depends on what the cows have been eating.

The isoflavones in soy keep cells from going rowdy,” says researcher Nagi B. Kumar, PhD, RD, of the Moffitt Cancer Center in Tampa, who headed that study in Prostate. “Most cells function, mature, and eventually die off. But some cells are mutated, and they proliferate in a way that’s pointless, progressive, and wild. That’s what causes cancer, and soy seems to help stop this.”


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 thousand-fold in comparison to levels taken before the study.

On the other hand…..

Soy apparently has many beneficial constituents along with harmful ones.

Dietary genistein and highly processed soy agents have been found to stimulate growth in the MCF-7 prostate cancer cells, and to promote prostate cancer in ovaraectomised athymic mice models.

Non-fermented soy contains allergens, several toxins, and (particularly if uncooked, unfermented, & unsprouted) powerful protease inhibitors, which inhibit the critical anti-cancer action of proteolytic enzymes, particularly trypsin.

Far from being the perfect food, modern soy products contain anti-nutrients and toxins and they interfere with the absorption of vitamins and minerals.”

Unfermented soy contains high levels of a number of compounds that can: block the absorption of calcium, magnesium, iron and zinc; stunt growth; and alter hormone levels, disrupting menstruation, lowering testosterone, increasing the risk of breast cancer, and causing thyroid and prostate complications!. Unfermented soy includes things like soy milk, soy burgers and soy hot dogs,

Soybeans ontains large quantities of natural toxins or “anti-nutrients”. First among them are potent enzyme inhibitors that block the action of trypsin and other enzymes needed for protein digestion.

These inhibitors are large, tightly folded proteins that are not completely deactivated during ordinary cooking. They can produce serious gastric distress, reduced protein digestion and chronic deficiencies in amino acid uptake. In test animals, diets high in trypsin inhibitors cause enlargement and pathological conditions of the pancreas, including cancer.

Practical common-sense conclusions:

Avoid Unfermented soy products -Only eat fermented soy products

In order to derive some benefit from soy, consume only fermented soy products – such as organic miso (mugi barley and genmai miso are the best), organic tempeh, soy sauce or tamari and natto.

Fermented soy products have the highest levels of cancer-fighting nutrients. Fermented soy products are known to contain high concentrations of the isoflavone, genistein, and other compounds that exhibit anticancer activity in preclinical models. Read more on the benefits of fermented soy products for healing prostate cancer »



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