Ask the Doctor


"to whom it may concern:

i believe that a vegetarian diet with soy isoflavone in soy products is good for breast cancer.  isn't it that only estradiole and estrione are the only harmful estrogens to breast cancer patients?  and not estriole?  please, check that a vegetarian diet and soy can only maintain a weak and harmless estriole in the body of a breast cancer patient.

i think  we should concentrate more on restricting hormone fed livestocks in breast cancer diets than soy products.

thank you  for your attention on the matter.

more power to your site.

yours truly,


a breast cancer patient from the philippines,

Susan, "


I agree with your sentiments that trying to do things that will protect our food supply would be energy wisely spent.  With cancer, prevention is the best treatment.  Unfortunately, although there are a great many things that might be implicated in causing cancer that could easily be changed, little money or effort goes toward that.  The vast majority goes to treating cancer once it appears.

The science on meat consumption and cancer risk has been very confusing in the past.  Currently my feeling is that it is not as simple as a vegetarian diet protects against cancer and meat eaters get cancer.  I wish it were.  Instead there are many factors involved;here are three that come to mind immediately.
a.  Diets high in meat that is overcooked drastically increase cancer, especially breast cancer rates.  Women, for example, who prefer well done meat have 12 times the breast cancer rate as women who prefer less cooked meat. 
b. Vegetarians eat more fruits and vegetables than meat eaters.  Consumption of fruits and vegetables plays a more significant role than whether someone is a vegetarian or not. Vegetarians eat less fat in general, another risk factor for breast cancer.  c.  Vegetarians frequently have lower Vitamin B-12 status.  This is, by itself, a risk for breast cancer.

The research on soy products and soy isoflavones is not clear.  Most arguments in favor of soy being protective against breast cancer begin with the assumption that Japanese women get less breast cancer because they eat soy.  There are a number of other explanations for their lower breast cancer incidence.  For example, they start menstruating at a later age, a clearly protective factor.  They eat more fish.  They eat more fermented foods (a risk factor for gastric cancer but possibly protective against breast cancer).  The laboratory research on soy show a dual effect on cancer.  High concentrations of genestein slow breast cancer cell growth and sound very exciting.  Unfortunately at low concentrations, genestein actually stimulates the growth of breast cancer cells.  It appears that even with the most conscientious oral consumption of soy products it is impossible to raise tissue levels into the range where soy inhibits breast cancer cell growth.

There are three main estrogens in human metabolism:
E1  Estrone
E2 Estradiol
E3 Estradiol

E1 and E2 are considered strong estrogens, having the greatest estrogen effect on the body, producing secondary sexual characteristics, stopping hot flashes, and also stimulating cancer cell growth.  There has been a long standing theory that E3, estradiol, is a weaker estrogen, and might be protective against breast cancer by preventing the binding of the strong stimulatory estrogens to breast cells.  This theory may hold for cancer prevention but it is not clear that it holds for existing cancer.  The idea has been around for years that soy will also bind to the estrogen receptors and prevent estrogen effect.  The problem is that soy does appear to have enough estrogen like effect that, again at low doses, it stimulates breast cancer cells more than it inhibits it.

At this point the jury is still out whether breast cancer patients should consume any soy or whether they should consume a lot of soy.  In some situations I present my patients with a choice that goes, "This might help you, it won't hurt so why don't you try it?"  In the case of soy, the story is different, "This might help you or it might hurt you, it's one or the other and we aren't sure."

Hippocrates said the primary role of the physician, was to first and foremost, do no harm.  I cannot suggest soy to women with breast cancer at this time.

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