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:

70% Taking Common Antidepressants Suffer Sexual Side Effects

What’s the latest on treating depression with the spice saffron? Years ago, I covered a head-to-head comparison of saffron versus Prozac for the treatment of depression in my video Saffron vs. Prozac, and saffron seemed to work just as well as the drug. In the years since, five other studies have found that saffron beat out placebo or rivaled antidepressant medications.

It may be the spice’s red pigment, crocin, since that alone beat out placebo as an adjunct treatment, significantly decreasing symptoms of depression, symptoms of anxiety, and general psychological distress. Perhaps, its antioxidants played a role in “preventing free radical-induced damage in the brain.” The amount of crocin the researchers used was equivalent to about a half teaspoon of saffron a day.

If the spice works as well as the drugs, one could argue that the spice wins, since it doesn’t cause sexual dysfunction in the majority of men and women like most prescribed antidepressants do. SSRI drugs like Prozac, Paxil, and Zoloft cause “adverse sexual side effects” in around 70 percent of people taking them. What’s more, physicians not only significantly underestimate the occurrence of side effects, but they also tend to underrate how much they impact the lives of their patients.

Not only is this not a problem with saffron, the spice may even be able to treat it, as I explore in my video Best Food for Antidepressant-Induced Sexual Dysfunction. “In folk medicine, there is a widely held belief that saffron might have aphrodisiac effects.” To test this, men with Prozac-induced sexual impairment were randomized to saffron or placebo for a month. By week four, the saffron group “resulted in significantly greater improvement in erectile function…and intercourse satisfaction,” and more than half of the men in the saffron group regained “normal erectile function.” The researchers concluded that saffron is an “efficacious treatment” for Prozac-related erectile dysfunction. It has all been found to be effective for female sexual dysfunction, as well, as you can see at 2:35 in my video. Female sexual function increased by week four, improving some of the Prozac-induced sexual problems but not others. So, it may be better to try saffron in the first place for the depression and avoid developing these sexual dysfunction problems, since they sometimes can persist even after stopping the drugs, potentially worsening one’s long-term depression prognosis.

This includes unusual side effects, such as genital anesthesia, where you literally lose sensation. It can happen in men and women. More rarely, antidepressants can induce a condition called restless genital syndrome. You’ve heard of restless legs syndrome? Well, this is a restless between-the-legs syndrome. These PSSDs, or Post-SSRI Sexual Dysfunctions, meaning dysfunctions that appear or persist after stopping taking these antidepressants, can be so serious that “prescribing physicians should mention the potential danger of the occurrence of genital (e.g., penile or vaginal) anesthesia to every patient prior to any SSRI treatment.” If you’re on one of these drugs, did your doctor warn you about that?

All hope is not lost, though. Evidently, penile anesthesia responds to low-power laser irradiation. After 20 laser treatments to his penis, one man, who had lost his penile sensation thanks to the drug Paxil, partially regained his “penile touch and temperature sensation.” However, he still couldn’t perform to his girlfriend’s satisfaction, and she evidently ended up leaving him over it, which certainly didn’t help his mood. But, before you feel too badly for him, compare a little penile light therapy to clitoridectomy, clitoris removal surgery, or another Paxil-related case where a woman’s symptoms only improved after six courses of electroshock therapy.

Pass the paella!


For more on the spice, check out:

Those drug side effects sound devastating, but depression is no walk in the park. However, when one balances risk and benefit, one assumes that there are actually benefits to taking them. That’s why the shocking science I explored in Do Antidepressant Drugs Really Work? is so important.

What else may boost mood? A healthy diet and exercise:

For more on sexual health generally, see:

What else can spices do? Here’s just a taste:

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: