Can Soy Prevent and Treat Prostate Cancer?

As I discuss in my video The Role of Soy Foods in Prostate Cancer Prevention and Treatment, a compilation of 13 observational studies on soy food consumption and the risk of prostate cancer found that soy foods appear to be “protective.” What are observational studies? As opposed to interventional studies, in observational studies, researchers observe what people are eating but don’t intervene and try to change their diets. In these studies, they observed that men who ate more soy foods had lower rates of prostate cancer, but the problem with observational studies is that there could be confounding factors. For example, “people who choose to eat soy also make other lifestyle decisions that lower the risk of cancer (e.g., lower fat intake, higher vegetable and fruit intake, more frequent exercise),” maybe that is why they have less cancer. Most of the studies tried to control for these other lifestyle factors, but you can’t control for everything. What’s more, most of the studies were done in Asia, so maybe tofu consumption is just a sign of eating a more traditional diet. Is it possible that the reason non-tofu consumers got more cancer is that they had abandoned their traditional diet? If only we could look at a Western population that ate a lot of soy. We can: the Seventh-Day Adventists.

In the 1970s, more than 12,000 Adventist men were asked about their use of soy milk and then were followed for up to 16 years to see who got cancer and who did not. So, what did they find? Frequent consumption of soy milk was associated with a whopping 70 percent reduction of the risk of prostate cancer, as you can see at 1:33 in my video. Similarly, in a multiethnic study that involved a number of groups, soy intake appeared protective in Latinos, too.

Prostate cells carry beta type estrogen receptors, which appear to act as a tumor suppressor, a kind of “gatekeeper…inhibiting invasion, proliferation and…preventing” the prostate cells from turning cancerous. And, those are the receptors targeted by the phytoestrogens in soy, like genistein, which inhibits prostate cancer cell invasion and spread in a petri dish at the kind of levels one might get consuming soy foods. The prevention of metastases is critical, as death from prostate cancer isn’t caused by the original tumor, but its spread throughout the body, which explains why it “is recommended that men with prostate cancer consume soy foods, such as soybeans, tofu, miso and tempeh.”

Wait a moment. Dean Ornish and his colleagues got amazing results, apparently reversing the progression of prostate cancer with a plant-based diet and lifestyle program. Was it because of the soy? Their study didn’t just include a vegan diet, but a vegan diet supplemented with a daily serving of tofu and a soy protein isolate powder. There have been studies showing that men given soy protein powders develop less prostate cancer than the control group, but what was the control group getting? Milk protein powder. Those randomized to the milk group got six times more prostate cancer than the soy group, but was that due to the beneficial effects of soy or the deleterious effects of the dairy? Dairy products are not just associated with getting prostate cancer, but also with dying from prostate cancer. Men diagnosed with prostate cancer who then ate more dairy tended to die sooner, and “both low-fat and high-fat dairy consumption were positively associated with an increased risk of fatal outcome.”

The best study we have on soy protein powder supplementation for prostate cancer patients found no significant benefit, and neither did a series of soy phytoestrogen dietary supplements. But, perhaps that’s because they used isolated soy components rather than a whole soy food. “Taking the whole-food approach may be more efficacious,” but it can be hard to do controlled studies with whole foods: You can make fake pills, but how do you give people placebo tofu?

A group of Australian researchers creatively came up with a specially manufactured bread containing soy grits to compare to a placebo regular bread and gave slices to men diagnosed with prostate cancer awaiting surgery. As you can see at 4:31 in my video, they saw a remarkable difference in just about three weeks time. It was the first study to show that a diet incorporating a whole soy food could favorably affect prostate cancer markers, but you can’t just go out and buy soy grit bread. Another study was a little more practical. Twenty men with prostate cancer who had been treated with radiation or surgery but seemed to be relapsing were asked to drink three cups of regular soy milk a day. The PSA levels in each of the 20 patients were all rising before they started the soy milk, suggesting they had relapsing or metastatic cancer growing inside of them. However, during a year drinking soy milk, 6 out of the 20 subjects got better, 2 got worse, and the remaining 12 remained unchanged, as you can see from 5:02 in my video. So, they concluded that soy food may help in a subset of patients.

Based on all these studies, the results Ornish and his colleagues got were probably due to more than just the soy. Similarly, the low prostate cancer rates in Asia are probably because of more than just the soy, since the lowest rates are also found in parts of Africa, where I don’t think they’re eating a lot of tofu. Indeed, in the multiethnic study, other types of beans besides soy also appeared protective for Latinos and all the groups put together, when looking at the most aggressive forms of prostate cancer. So, the protection associated with plant-based diets may be due to eating a variety of healthy foods. 


That soy milk stat from the Adventist study is astounding. What about fermented soy foods, though? That was the subject of Fermented or Unfermented Soy Foods for Prostate Cancer Prevention?.

Reversing the progression of cancer? See How Not to Die from Cancer.

Given the power of diet, it’s amazing to me how difficult Changing a Man’s Diet After a Prostate Cancer Diagnosis can be. It’s not all or nothing, though. Check out Prostate Cancer Survival: The A/V Ratio.

For soy and breast cancer survival, see Is Soy Healthy for Breast Cancer Survivors?.

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:

Fermented or Unfermented Soy?

As you can see at the start of my video Fermented or Unfermented Soy Foods for Prostate Cancer Prevention?, there is an enormous variation in the rates of prostate cancer around the globe, with among the highest rates in the United States and lowest rates in Asia—though that may be changing. The largest increase in prostate cancer rates in the world in recent decades has been in South Korea, for example: a 13-fold increase in prostate cancer deaths nationwide. Researchers suggested the increase in animal foods may have played a role, since that was the biggest change in their diet over that period, with nearly an 850 percent increase.

This is consistent with what we know in general about foods and the prevention and management of prostate cancer. Tomatoes, cruciferous vegetables like broccoli, and soy foods appear to decrease risk, there’s no clear benefit from fish, but there is an increased risk associated with meat and dairy, as you can see at 0:52 in my video. This may be because a diet based around whole plant foods “may effectively reduce inflammation in the body.”

There is also a genetic factor. If you have a first-degree relative with prostate cancer, you may be at three-fold higher risk, but non-genetic factors may increase your risk 300-fold. How do we know the low rates in Asia aren’t genetic? Because when Asians move to the United States, their rates shoot up, “and by the second generation, the incidence rate [is] already approaching that of average Americans.” This may be because of more Burger Kings and Dairy Queens, but could also be because of eating fewer protective foods, such as soy.

A systematic review of all soy and prostate cancer population studies to date confirmed that soy foods are associated with lower the risk, but that’s a relatively broad category. There are all sorts of soy foods. There are fermented soy foods, like miso and tempeh, and unfermented ones, like tofu and soy milk. Which are more protective? Researchers sifted through the studies, and it turns out that only the unfermented soy seemed to help. Tofu and soy milk consumption was associated with about a 30 percent reduction in risk, whereas there didn’t appear to be any protection linked to fermented soy foods.


What about other healthy plant foods, like broccoli and turmeric? See what they can do in Best Supplements for Prostate Cancer.

Dean Ornish and his colleagues got amazing results, apparently reversing the progression of prostate cancer with a plant-based diet and lifestyle program. Do you think it could be because of the soy? It wasn’t just a vegan diet, but a vegan diet supplemented with a daily serving of tofu and a soy protein isolate powder. Find out in The Role of Soy Foods in Prostate Cancer Prevention and Treatment.

More on the number-one cancer among men:

What about soy and breast cancer? I’m glad you asked!

Who Shouldn’t Eat Soy? Watch the video to find out!

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:

Garlic Powder to Lower Lead Levels

There are so-called chelation drugs that can be taken for acute, life-threatening lead poisoning—for instance if your two-year-old swallowed one of the little lead weights her grandma was using while sewing curtains and the doctor happened to miss it on x-ray, so it stayed lodged inside her until she died with a blood lead level of 283 mcg/dcl, a case I discuss in my video Best Foods for Lead Poisoning: Chlorella, Cilantro, Tomatoes, Moringa?.

However, for lower grade, chronic lead poisoning, such as at levels under 45 mg/dL, there were no clear guidance as to whether these chelation drugs were effective. When they were put to the test, the drugs failed to bring down lead levels long term. Even when they worked initially, in dose after dose, the lead apparently continued to seep from the patients’ bones, and, by the end of the year, they ended up with the same lead levels as the sugar pill placebo group, as you can see at 0:50 in my video. It was no surprise, then, that even though blood lead levels dipped at the beginning, researchers found no improvements in cognitive function or development.

Since much of lead poisoning is preventable and the drugs don’t seem to work in most cases, that just underscores the need “to protect children from exposure to lead in the first place.” Despite the medical profession’s “best intentions to do something to help these kids…drug therapy is not the answer.” Yes, we need to redouble efforts to prevent lead poisoning in the first place, but what can we do for the kids who’ve already been exposed?

The currently approved method, these chelating drugs that bind and remove lead from our tissues, “lack[s]…safety and efficacy when conventional chelating agents are used.” So, what about dietary approaches? Plants produce phytochelatins. All higher plants possess the capacity to synthesize compounds that bind up heavy metals to protect themselves from the harmful effects, so what if we ate the plants? “Unlike other forms of treatment (e.g., pharmacotherapy with drugs), nutritional strategies carry the promise of a natural form of therapy that would presumably be cheap and with few to no side effects.” Yes, but would it work when the drugs didn’t?

We had learned that a meal could considerably cut down on lead absorption, but “the particular components of food intake that so dramatically reduce lead absorption” were uncertain at the time. Although the calcium content of the meal appeared to be part of it, milk didn’t seem to help and even made things worse. What about calcium supplements? Some assert that calcium supplements may help in reducing lead absorption in children, but “recommendations…must be based on evidence rather than conviction.” What’s more, those assertions are based in part on studies on rodents, and differences in calcium absorption and balance between rats and humans make extrapolation tricky. What you have to do is put it to the test. Researchers found that even an extra whopping 1,800 mg of calcium per day had no effect on blood lead levels. Therefore, the evidence doesn’t support conclusions that calcium supplements help.

What about whole foods? Reviews of dietary strategies to treat lead toxicity say to eat lots of tomatoes, berries, onions, garlic, and grapes, as they are natural antagonists to lead toxicity and therefore should be consumed on a regular basis. Remember those phytochelatins? Perhaps eating plants might help detoxify the lead in our own bodies or the bodies of those we eat.

These natural phytochelatin compounds work so well that we can use them to clean up pollution. For example, the green algae chlorella can suck up lead and hold onto it, so what if we ate it? If it can clean up polluted bodies of water, might it clean up our own polluted bodies? We don’t know, because we only have studies on mice, not men and women.

So, when you hear how chlorella detoxifies, they’re talking about the detoxification of rat testicles. Yes, a little sprinkle of chlorella might help your pet rat, or perhaps you could give them some black cumin seeds or give them a sprig of cilantro, but when you hear how cilantro detoxifies against heavy metals, I presume you don’t expect the researchers to be talking about studies in rodents. If we’re interested in science protecting our children, not just their pets, we’re out of luck.

The same is true with moringa, tomatoes, flaxseed oil, and sesame seed oil, as well as black grapes, and black, white, green, and red tea. There are simply no human studies to guide us.

Dietary strategies for the treatment of lead toxicity are often based on rodent studies, but, for tofu, at least, there was a population study of people that showed lower lead levels in men and women who ate more tofu. The researchers controlled for a whole bunch of factors, so it’s not as if tofu lovers were protected just because they smoked less or ate less meat, but you can’t control for everything.

Ideally, we’d have a randomized, placebo-controlled study. Researchers would take a group of people exposed to lead, split them into two groups, with half given food and the other half given some kind of identical placebo food, and see what happens. It’s easy to do this with drugs because you just use look-alike sugar pills as placebos so people don’t know which group they’re in, but how do you make placebo food? One way to do disguised food interventions is to use foods that are so potent they can be stuffed into a pill—like garlic. There had been various studies measuring the effects of garlic in rats and looking at garlic as a potential antidote for lead intoxication distributed among different mouse organs, but who eats mouse organs? One animal study did have some direct human relevance, though, looking at the effect of garlic on lead content in chicken tissues. The purpose was to “explore the possible use of garlic to clean up lead contents in chickens which”—like all of us on planet Earth—“had been exposed to lead pollution and consequently help to minimize the hazard” of lead-polluted chicken meat.

And…it worked! As you can see at 1:59 in my video Best Food for Lead Poisoning: Garlic, feeding garlic to chickens reduced lead levels in the “edible mass of chicken” by up to 75 percent or more. Because we live in a polluted world, even if you don’t give the chickens lead and raise them on distilled water, they still end up with some lead in their meat and giblets. But, if you actively feed them lead for a week, the levels get really high. When you give them the same amount of lead with a little garlic added, however, much less lead accumulates in their bodies.

What’s even more astonishing is that when researchers gave them the same amount of lead—but this time waited a week before giving them the garlic—it worked even better. “The value of garlic in reducing lead concentrations…was more pronounced when garlic was given as a post-treatment following the cessation of lead administration”—that is, after the lead was stopped and had already built up in their tissues. We used to think that “the beneficial effect of garlic against lead toxicity was primarily due to a reaction between lead and sulfur compounds in garlic” that would glom on to lead in the intestinal tract and flush it out of the body. But, what the study showed is that garlic appears to contain compounds that can actually pull lead not only out of the intestinal contents, but also out of the tissues of the body. So, the “results indicate that garlic contain chelating compounds capable of enhancing elimination of lead,” and “garlic feeding can be exploited to safeguard human consumers by minimizing lead concentrations in meat….”

If garlic is so effective at pulling lead out of chickens’ bodies, why not more directly exploit “garlic feeding” by eating it ourselves? Well, there had never been a study on the ability of garlic to help lead-exposed humans until…2012? (Actually, I’m embarrassed to say I missed it when the study was first published. That was back when I was just getting NutritionFacts.org up and running. Now that we have staff and a whole research team, hopefully important studies like this won’t slip through the cracks in the future.)

The study was a head-to-head comparison of the therapeutic effects of garlic versus a chelation therapy drug called D-penicillamine. One hundred and seventeen workers exposed to lead in the car battery industry were randomly assigned into one of two groups and, three times a day for one month, either got the drug or an eighth of a teaspoon of garlic powder compressed into a tablet, which is about the equivalent of two cloves of fresh garlic a day. As expected, the chelation drug reduced blood lead levels by about 20 percent—but so did the garlic. The garlic worked just as well as the drug and, of course, had fewer side effects. “Thus, garlic seems safer clinically and as effective,” but saying something is as effective as chelation therapy isn’t saying much. Remember how chelation drugs can lower blood levels in chronic lead poisoning, but they don’t actually improve neurological function?

Well, after treatment with garlic, significant clinical improvements were seen, including less irritability, fewer headaches, and improvements in reflexes and blood pressure, but these improvements were not seen in the drug group. They weren’t seen after treatment with the chelation therapy drug. So, garlic was safer and more effective. “Therefore, garlic can be recommended for the treatment of mild-to-moderate lead poisoning.


 There are also some human studieson vitamin C. Check out Can Vitamin C Help with Lead Poisoning?.

For even more lead videos, see:

To learn more about chlorella, 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: