What Does Drinking Soy Milk Do to Hormone Levels?

The vast majority of breast cancers start out hormone-dependent, where estradiol, the primary human estrogen, “plays a crucial role in their breast cancer development and progression.” That’s one of the reasons why soy food consumption appears so protective against breast cancer: Soy phytoestrogens, like genistein, act as estrogen-blockers and block the binding of estrogens, such as estradiol, to breast cancer cells, as you can see at 0:24 in my video How to Block Breast Cancer’s Estrogen-Producing Enzymes.

Wait a second. The majority of breast cancers occur after menopause when the ovaries have stopped producing estrogen. What’s the point of eating estrogen-blockers if there’s no estrogen to block? It turns out that breast cancer tumors produce their own estrogen from scratch to fuel their own growth.

As you can see at 1:03 in my video, “estrogens may be formed in breast tumors by two pathways, namely the aromatase pathway and sulfatase pathway.” The breast cancer takes cholesterol and produces its own estrogen using either the aromatase enzyme or two hydroxysteroid dehydrogenase enzymes.

So, there are two ways to stop breast cancer. One is to use anti-estrogens—that is, estrogen-blockers—like the soy phytoestrogens or the anti-estrogen drug tamoxifen. “However, another way to block estradiol is by using anti-enzymes” to prevent the breast cancer from making all the estrogen in the first place. And, indeed, there are a variety of anti-aromatase drugs in current use. In fact, inhibiting the estrogen production has been shown to be more effective than just trying to block the effects of the estrogen, “suggesting that the inhibition of estrogen synthesis is clinically very important for the treatment of estrogen-dependent breast cancer.”

It turns out that soy phytoestrogens can do both.

Using ovary cells taken from women undergoing in vitro fertilization, soy phytoestrogens were found to reduce the expression of the aromatase enzyme. What about in breast cancer cells, though? This occurred in breast cancer cells, too, and not only was aromatase activity suppressed, but that of the other estrogen-producing enzyme, as well. But this was in a petri dish. Does soy also suppress estrogen production in people?

Well, as you can see at 2:34 in my video, circulating estrogen levels appear significantly lower in Japanese women than Caucasian American women, and Japan does have the highest per-capita soy food consumption, but you can’t know it’s the soy until you put it to the test. Japanese women were randomized to add soy milk to their diet or not for a few months. Estrogen levels successfully dropped about a quarter in the soy milk supplemented group. Interestingly, as you can see at 3:04 in my video, when the researchers tried the same experiment in men, they got similar results: a significant drop in female hormone levels, with no change in testosterone levels.

These results, though, are in Japanese men and women who were already consuming soy in their baseline diet. So, the study was really just looking at higher versus lower soy intake. What happens if you give soy milk to women in Texas? As you can see at 3:29 in my video, circulating estrogen levels were cut in half. Since increased estrogen levels are “markers for high risk for breast cancer,” the effectiveness of soy in reducing estrogen levels may help explain why Chinese and Japanese women have such low rates of breast cancer. What’s truly remarkable is that estrogen levels stayed down for a month or two even after the subjects stopped drinking soy milk, which suggests you don’t have to consume soy every day to have the cancer protective benefit.

Wait, soy protects against breast cancer? Yes, in study after study after study—and even in women at high risk. Watch my video BRCA Breast Cancer Genes and Soy for the full story.

 What about if you already have breast cancer? In that case, see Is Soy Healthy for Breast Cancer Survivors?

 And what about GMO soy? Get the facts in GMO Soy and Breast Cancer.

 Okay, then, Who Shouldn’t Eat Soy? Watch my video and find out.


What else can we do to decrease breast cancer risk? See:

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In health,

Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations:

What About the Sodium in Miso?

According to the second World Cancer Research Fund/American Institute for Cancer Research expert report, “[s]alt is a probable cause of stomach cancer,” one of the world’s leading cancer killers. If the report’s estimate of an 8 percent increase in risk for every extra gram of salt a day is correct, then in a country like the United Kingdom, nearly 1,700 cases of stomach cancer happen every year just because of excess salt intake, as you can see at 0:27 in my video Is Miso Healthy?, and, in a country like the United States, it would be thousands more annually.

The risk of stomach cancer associated with salt intake appears on par with smoking or heavy alcohol use, but may only be half as bad as opium use or increased total meat consumption, as you can see at 0:43 in my video. These findings were based on a study of more than a half million people, which may explain why those eating meatless diets appear to have nearly two-thirds lower risk.

We know dietary salt intake is directly associated with the risk of stomach cancer, and the higher the intake, the higher the risk. A meta-analysis went one step further and looked at specific salt-rich foods: pickled foods, salted fish, processed meat, and miso soup. Habitual consumption of pickled foods, salted fish, and processed meat were each associated with about a 25 percent greater risk of stomach cancer. The pickled foods may explain why Korea, where the pickled cabbage dish kimchi is a staple, appears to have the highest stomach cancer rates in the world, as you can see at 1:39 in my video. But researchers found there was no significant association with the consumption of miso soup. This may be because the carcinogenic effects of the salt in miso soup are counteracted by the anti-carcinogenic effects of the soy, effectively canceling out the risk. And, if we made garlicky soup with some scallions thrown in, our cancer risk may drop even lower, as you can see at 2:06 in my video.

Cancer isn’t the primary reason people are told to avoid salt, though. What about miso soup and high blood pressure? Similar to the relationship between miso and cancer, the salt in miso pushes up our blood pressures, but miso’s soy protein may be relaxing them down. If we compare the effects of soy milk to cow’s milk, for example, and, to make it even more fair, compare soy milk to skim cow’s milk to avoid the saturated butter fat, soy milk can much more dramatically improve blood pressure among women with hypertension, as you can see at 2:43 in my video. But would the effect be dramatic enough to counter all the salt in miso? Japanese researchers decided to put it to the test.

For four years, they followed men and women in their 60s, who, at the start of the study, had normal blood pressure, to see who was more likely to be diagnosed with hypertension in that time: those who had two or more bowls of miso soup a day or those who had one or less. Two bowls a day may add a half teaspoon of salt to one’s daily diet, yet those who had two or more bowls of miso soup every day appeared to have five times lower risk of becoming hypertensive. So, maybe the anti-hypertensive effects of the soy in the miso exceed the hypertensive effects of the salt.


Indeed, miso paste, a whole soy food, can be used as a “green light” source of saltiness when cooking. That’s why I used it in my pesto recipe in How Not to Die and in my How Not to Die Cookbook. It can help you in Shaking the Salt Habit.

Not convinced that salt is bad for you? Check out these videos:

Not convinced that soy is good for you? See:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations:

How to Treat Endometriosis with Diet

“Endometriosis is a major cause of disability and compromised quality of life in women and teenage girls.” It “is a chronic disease which is under-diagnosed, under-reported, and under-researched…[and for patients, it] can be a nightmare of misinformation, myths, taboos, lack of diagnosis, and problematic hit-and-miss treatments overlaid by a painful, chronic, stubborn disease.”

Pain is what best characterizes the disease: pain, painful intercourse, heavy irregular periods, and infertility. About one in a dozen young women suffer from endometriosis, and it accounts for about half the cases of pelvic pain and infertility. It’s caused by what’s called “retrograde menstruation”—blood, instead of going down, goes up into the abdominal cavity, where tissue of the uterine lining can implant onto other organs. The lesions can be removed surgically, but the recurrence rate within five years is as high as 50 percent.

Endometriosis is an estrogen-dependent disease, so might the anti-estrogenic effects of the phytoestrogens in flaxseeds and soy foods help, as they appear to do in breast cancer? I couldn’t find studies on flax and endometriosis, but soy food consumption may indeed reduce the risk of that disease. What about treating endometriosis with soy? While I couldn’t find any studies on that, there is another food associated with decreased breast cancer risk: seaweed.

Seaweeds have special types of fiber and phytonutrients not found in land plants, so in order to get these unique components, we would need to incorporate sea vegetables into our diet. Seaweeds, may have anti-cancer properties, including anti-estrogen effects. Japanese women have among the lowest rates of breast, endometrial, and ovarian cancers, as well as longer menstrual cycles and lower estrogen levels circulating in their blood, which may help account for their low risk of estrogen-dependent cancers. We assumed this was due to their soy-rich diets, but their high intake of seaweed might also be helping.

When seaweed broth was dripped on human ovary cells that make estrogen, estrogen levels dropped. Why? It either inhibits production or facilitates breakdown of estrogen. It may even block estrogen receptors, lowering the activity of the estrogen that is produced. This is in a petri dish, though. Does it happen in women, too? Yes.

Researchers estimated that an effective estrogen-lowering dose of seaweed for an average American woman might be around five grams a day, but, apparently, no one has tried testing it on cancer patients yet. However, it has been tried on endometriosis, as I discuss in my video How to Treat Endometriosis with Seaweed.

Three women with abnormal menstrual cycles, including two with endometriosis, volunteered to add a tiny amount of dried, powdered bladderwrack, a common seaweed, to their daily diet. This effectively lengthened their cycles and reduced the duration of their periods—and not just by a little. As you can see at 3:14 in my video, subject 1 had a 30-year history of irregular periods, averaging every 16 days. Taking just a quarter-teaspoon of this seaweed powder a day added 10 days onto her cycle, up to 26 days, and adding a daily half-teaspoon increased her cycle to 31 days, nearly doubling its length. Furthermore, as you can see at 3:38 in my video, all three women experienced marked reductions in blood flow and a decreased duration of menstruation. For 30 years, subject 1 had been having her period every 16 days, and it typically lasted 9 days. Can you imagine? Then, by just taking a daily half-teaspoon of seaweed, her period came just once a month and only lasted about four days. Most importantly, in the two women suffering from endometriosis, they reported “substantial alleviation” of their pain. How is that possible? There was a 75 percent drop in estrogen levels after just a quarter-teaspoon of seaweed powder a day and an 85 percent drop after a half-teaspoon. 

Of course, with just a few women and no control group in that study, we need bigger, better studies. But, that study was published more than a decade ago and not a single such study has been published since. Millions of women are suffering with these conditions. Does the research world just not care about women? The more pointed question is: who’s going to fund the work? Less than a teaspoon of seaweed costs less than five cents, so a larger study may never be done. But, without any downsides, I suggest endometriosis sufferers give it a try.


For more on endometriosis, see my video What Diet Best Lowers Phthalate Exposure?, and, to learn about the anti-estrogenic effects of the phytoestrogens in flaxseeds on breast cancer, see Flaxseeds and Breast Cancer Survival: Clinical Evidence.

Interested in more on sea vegetables? See:

I recommend staying away from kelp and hijiki, though. Why? See Too Much Iodine Can Be as Bad as Too Little.

Learn more about other natural remedies for menstrual problems:

In health,
Michael Greger, M.D.

PS: If you haven’t yet, you can subscribe to my free videos here and watch my live presentations: