Breast cancer has been notoriously low in Asian women on their traditional diet. From 1970 to 1999, however, the incidence more than doubled in Singapore and Japan. Moreover, once Asian women move and abandon their traditional diet, breast cancer incidence resembles that of Western women. In an attempt to clarify the reasons for these changes, Anna H. Wu et al, undertook a cross-sectional in depth study of 144 healthy postmenopausal Chinese women in Singapore.

Since the literature is quite clear about the relationship of endogenous estrogen levels and breast cancer, the authors tried to screen out dietetic and other lifestyle factors that might mediate estrogen levels.

To complete their information analysis, they utilize studies done in other parts of the world such as Japan, Finland and England.

While the Singapore study of Anna H. Wu, et al measures both estradiol (E1) and estrone (E2) and androstenedione, (2) other studies measure either E1 or E2 so they are only partially comparable. The Singapore study is, in fact, one of the most complete not only because of their reliance on the above markers, but because they also took into consideration the body mass index (BMI) and showed that increased BMI has "substantial and significant influence on endogenous E1 and E2". This most likely has to do with increased aromatase enzyme activity and biotransformation of androgens into estrogens.

Many studies, including the fallowing study we are about to review by Anna H. Wu, et al (2) have shown a reduction in breast cancer with high soy intake among Chinese women. The hypothesis was that high soy intake might reduce the risk of high level of endogenous estrogen especially of E1 and in fact the Singapore study proved just that. In the Singapore study the E1 (estradiol) plasma levels were 15% lower among individuals on the highest intake of soy. (See appropriate levels in the discussion of the next article)) They found out that E1 levels decline, not in a linear manner in relation to soy intake, but that the reduction was apparent in those on the highest amount of soy. The authors also reported that, in a Japanese study, the levels of E2 (estrone) were "significantly and inversely" correlated to their soy intake. In my opinion these findings raise the question of whether or not women who have had breast cancer should be on high levels of isoflavones or its active components, genestein and dyazin. Till further studies on cancer staging and soy intake are undertaken I recommend prudence and to investigate the usage of fermented soy. The next study called, "Adolescent and Adult Soy Intake and Risk of Breast Cancer in Asian American Women"(2),brings about very interesting findings regarding the efficacy of soy intake as a preventive measure This study shows the futility of commencing soy intake, later in life as a cancer preventive measure not withstanding its benefit as a menopausal symptom relief...

Soy, in the form of tofu, miso soup and other derivatives, has been the basis of the traditional Asian diet since time immemorial. These cultures, unbeknown to them, were undertaking a large clinical study on the relationship of soy intake and breast cancer prevention.

Epidemiological studies report that Japanese women on the traditional diet have the lowest incidence of breast cancer of all. Their pattern of eating also controls the symptoms of menopause, the most bothersome aspect of aging for many western women. Interestingly enough, in the Japanese language, there is no word for hot flashes. All this anecdotal information has created interest in the public, and Western women have begun consuming many soy products. Tofu and other derivatives have emerged as good foods to handle menopausal symptoms. And now, we have evidence that they do more than that.

The market has followed the public interest with a plethora of soy derivatives to satisfy our need for variety. Our supermarket’s shelves are replenished with various forms of tofu products from soft and hard tofu, to soy milk, soy spread, soy cheese and even soy ice cream.

The scientific world, at the tail of this popular trend, began in the 1990’s to investigate the validity of these popular beliefs. The issue of soy byproducts intake in relationship to breast cancer prevention was, at best, controversial. No one had done a specific study to quantify the incidence of breast cancer in relation to the time of consumption and to the quantity of soy intake until this recent study in Los Angeles by Wu, et al. Between 1995 and 1998, the authors interviewed over 1000 Asian-American women of Chinese, Japanese and Filipino extraction in the Los Angeles area. 501 of these had breast cancer and 595 worked as a control group.

The study’s primary interest was that of establishing, first of all, if the period of life, when the consumption of tofu took place, made a difference. Secondly, they went out to establish the approximate quantity of the active components of tofu: the ISOFLAVONES that would confer cancer protection.

1. Early pattern of intake (during Adolescence only)

2. During Adolescence and Adult life

3. Starting in adult life

This sophisticated analysis unveiled a significant finding and that is; the most important time to consume adequate amounts of soy is adolescence. The amount that grants some degree of breast cancer prevention seems to range between 12mg and 26mg a day of the active components (isoflavones). During adolescence, even low frequency of usage (once a week) in adequate quantity seems to give mild but long lasting protection, 23% reduction in breast cancer incidence. The highest degree of protection is in the group that uses tofu throughout life including adolescence.

Adolescence, therefore, offers an opportunity for altering the alarming trend of increasing breast cancer incidence. The group in which tofu exerts no protection against breast cancer is that of women starting tofu consumption in adult life. This does not exclude the beneficial effects of soy, regarding menopausal symptoms.

During puberty (and pregnancy) breast tissues undergo rapid cell division. This coincides with the time when the tissues have the highest uptake of estrogen, both endogenous and exogenous (food and toxic byproducts known as xeno-estrogens.) These latter are particularly carcinogenic.

One of the hypotheses for the protective effect of soy and in particular one of its most active ingredients: genestein is the fact that this isoflavone binds to the breast tissues, preempting the uptake of too much estrogen and in particular of the most carcinogenic exogenous forms (xeno-estrogens).

That alone could be sufficient. But there is more.

	Adequate amounts of soy reduce endogenous estrogen. (A too high level of estrogen, regardless of the source is never desirable.)
	Genestein, the most active component, might diminish the production of carcinogenic byproducts of estrogen metabolism.
	Studies in animals also show that genestein "favorably influenced mammary gland morphology". In other words, this active component of tofu, assures that breast tissues reach maturity, which is the opposite of what occurs in cancer.

Cancer is in fact a disorderly regression of tissues to a younger and immature status: the more immature the tissues the more aggressive the cancer.

The latter article also reported findings from the Shanghai study in which soy intake "was significantly inversely related to risk of mammography density pattern" and other cancer risk factors.

As for the issue of dosage, what emerged from the study is the fact that one needs to consume at least 12 mg of the active isoflavone a day for minimal protection. The preferred amount is around 45 mg a day. (One cup of soy milk contains about 20 to 30 mg of isoflanoves, and one-half cup of tofu or tempeh contains about 35 mg.) (3).

In summary, large amounts of soy products (at least 45 mg of the active ingredients per day – preferably throughout life), appropriate lifestyle to guarantee a correct body mass index (BMI) and as the first study indicates, elimination of smoking, very limited alcohol consumption and adequate intake of green tea, have emerged as sound preventive breast cancer measures5.

The most convincing aspect of the second article was the fact that women who only consumed tofu products in adolescence had still a mild reduction in breast cancer of 23%, while women who only started as adults, regardless of the quantity of intake, had no protection at all against breast cancer incidence.

Soy based products, especially in the most genuine forms of tofu, miso soup and Tofu milk, when used throughout life, especially at the time when the mammary gland undergoes the most rapid growth (puberty and pregnancy) affords us with the best protection against breast cancer.

This review doesn’t include other important factors such as high and frequent exposure to carcinogens, high levels of stress and other factors that were not the domain of these two articles. If we have learned anything it is the fact that we need to be more proactive in guiding our girls to consume foods that will ensure future protection, and avoid lifestyle factors that are detrimental.