Treating Prostate Cancer

Hello and welcome to Nutrition Facts. I’m your host, Dr. Michael Greger. Today, we’re going to explore smart nutrition choices based, naturally, on facts. Whenever there’s a new drug or surgical procedure, you can be assured that you and your doctor will probably hear about it because there’s a corporate budget driving its promotion; but, what about advances in the field of nutrition? That’s what this podcast is all about. 

For American men, prostate cancer is the most common internal cancer and the second leading cause of cancer death, according to the U.S. Centers for Disease Control. Lifestyle habits appear to be important in both preventing and treating prostate cancer, and a plant-based diet, especially when combined with moderate exercise, may be helpful as part of this program.

Dr. Dean Ornish showed that a plant-based diet and lifestyle program could apparently reverse the progression of prostate cancer, but that was for early stage, localized, watch-and-wait cancer. What about for more advanced stage life-threatening disease? Here’s what they found out.   

So, we had all this “preliminary evidence,” based on all the case reports “that prostate cancer may be sensitive to diet even after [it metastasizes].” It may prolong survival, and even cause “remission of bone [metastases] in men with advanced disease.” So, researchers decided to put it to the test “a 4-month [long] intervention.” They figured too much saturated fat, too little fiber, and too much meat may be the biggest players in “tumor promotion and progression.” So, they put people on a whole food plant-based diet of whole grains, beans, seeds, and fruit. Figuring this would be quite the “departure from their [regular] diet,” they included a stress-reduction component, in hopes of improving dietary compliance.

Okay. So, who were these ten men? They all didn’t just have prostate cancer; they all had “underwent [a] radical prostatectomy” to remove their primary tumor, and then “subsequently had increasing PSA” levels, indicative of probable metastatic disease. PSA stands for prostate-specific antigen; it’s only made by prostate cells, and they just had their entire prostates removed. So, the level should be zero. The fact that they not only still had some PSA, but that it was rising, suggests that the surgery failed, and the cancer had spread and is making a comeback.

Well, in the Ornish study, the more people complied with the diet and lifestyle recommendations, the better they did. Dietary changes only work if you actually do them. Just because you tell people to start eating a whole food plant-based diet doesn’t mean patients actually do it. One can use fiber intake as a proxy for dietary compliance, since all whole plant foods have fiber, and Ornish’s patients about doubled their fiber intake, from 31 to 59.

How did this group do? They started out even worse, averaging 14 grams a day, and only made it up to 19 grams a day. That’s not a whole food plant-based diet—that doesn’t even make it up to the recommended minimum daily intake. Only four men increased their fiber intake at all. So, maybe that may explain the different responses. Like, how did patient 2 do? The man whose fiber improved the most had the best PSA result, and the man whose fiber intake dropped the most had the worst PSA result. And, indeed, it appears the more change they made to their diet, the better their results.

The researchers concluded that “a plant-based diet delivered in the context of [stress management]…may slow the rate of tumor progression,” and unlike other treatments, may give patients some control over their disease. And, as Ornish pointed out, “the only side effects are beneficial ones.”

What happens when metastatic prostate cancer patients were taught to increase intake of whole grains, vegetables, fruit, and beans, and to decrease meat, dairy, and junk?  Here’s Part II of our series. 

Dr. Ornish and colleagues were able to show an apparent reversal in the progression of early stage localized prostate cancer with a plant-based diet and lifestyle program, and researchers at the University of Massachusetts and elsewhere showed a similar diet may help slow the progression of even advanced prostate cancer over a period of four months. How about six months? Researchers at UC San Diego found more cancer patients in the same situation, and put them through the same protocol. These were patients who were already treated for “invasive prostate cancer…by [either] radical prostatectomy or radiation therapy,” yet had “rising PSA” levels, suggesting the treatment didn’t work, and the cancer was on the move.

In those with a cancer recurrence, PSA levels typically “rise exponentially…, reflecting the gradual, inexorable growth of the cancer in the body.” “[T]he rate of [this] PSA rise is the single best predictor of…the…development of overt metastatic disease, as well as of overall survival.” The next step would be what’s called “hormonal therapy,” which is chemical or surgical castration, which has a list of side effects, including loss of libido, and sexual function, and strength, and vitality. Therefore, we try to hold off on that for as long as possible. So, if we’re just waiting, might as well give diet a try.

So, “[t]hey were taught to increase intake of whole grains, vegetables, fruit, and [beans], and to decrease meat, dairy, and refined [carbs].”

Of all possible lifestyle interventions, why a whole food, plant-based diet? Well, if you look around the world, there are huge differences in prostate cancer rates, with “We’re #1, USA, USA” rates up to a hundred times higher than some places in Asia, for example. And, it’s not just genetic; within one generation of coming to the U.S., cancer rates shoot up, and the grandkids end up with the same top-of-the-pile rates. A whole range of “lifestyle factors” have been looked at, but diet appears to have the greatest influence. Specifically, “[c]onsumption of meat and dairy…appears to increase risk, and consumption of plant…foods appears to decrease risk.” Hence, the plant-based diet.

“A possible mechanism…is arachidonic acid,” an inflammatory compound which we make from omega-6 rich oils, like corn oil, sunflower, safflower, and cottonseed oil, and also comes “preformed in…animal-based foods”—particularly from chicken in the American diet, and also eggs. And, in a Petri dish, at least, arachidonic acid appears to stimulate prostate cancer cell growth as much 200%. But, ask men to remove processed and animal foods from their diet for six months, and what happens?

In the absence of treatment, levels of PSA tend to increase exponentially, but eating healthier, nine of the ten patients showed an apparent slowing of cancer growth, and four of the nine an apparent reversal in cancer growth. The average “doubling time”—an estimate of how long it takes for their cancer to double in size—slowed from doubling every year, to closer to every ten years.

Their “findings suggest” that without further surgery, radiation, or chemo, “disease progression” can be slowed, or even reversed, despite the “prevailing scientific consensus…that cancer progression is largely irreversible.” They’re “not refut[ing] the benefits of standard therapies,” and not “guarantee[ing] that a plant-based diet and stress reduction will always induce remission. But [the results] do contribute to [this] growing [medical] literature that…in at least some circumstances, cancer may be partly reversible.” Just by modifying “dietary and lifestyle factors”, men “may be able to prevent disease spread”—all without getting their testicles chopped off.

In our last story today, soy is put to the test for the treatment of prostate cancer.

A compilation of 13 “observational studies” on soy food consumption and the risk of prostate cancer found that soy foods appear to be “protective.” Observational studies, as opposed to interventional studies; they observed what people were eating, but didn’t intervene and try to change their diets. So, they observed that men who ate more soy foods had lower rates of prostate cancer.

But, the problem with observation studies is that there could be confounding factors. Maybe people who choose to eat soy may also make other healthy lifestyle decisions, like eating more fruits and vegetables, and maybe that’s actually why they have less cancer. Most of the studies tried to control for these other lifestyle factors, but you can’t control for everything.

Most of the studies were done in Asia; so, maybe tofu consumption is just a sign of eating more of a traditional diet. Maybe the reason non-tofu consumers got more cancer is that they had abandoned their traditional diet. If only there was a Western population that ate a lot of soy we could look at. There is: Seventh Day Adventists.

In the ‘70s, more than 12,000 Adventist men were asked about their use of soy milk, and then, they were followed for up to 16 years to see who got cancer, and who did not. So, “Does high soy milk intake reduce prostate cancer incidence?” “Frequent consumption…of soy milk was associated with [a whopping] 70 percent reduction of the risk of prostate cancer.” 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 tumor suppressors, kind of a “‘gatekeeper’…inhibiting invasion, proliferation,” and preventing the prostate cells from turning cancerous in the first place. 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 kinds 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 recommendations for men with prostate cancer to consume soy foods as well.

Wait a second. Do you think the amazing results Dean Ornish and colleagues got—apparently reversing the progression of prostate cancer with a plant-based diet and lifestyle program—was 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].” There have been studies showing 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. But is that from the beneficial effects of soy, or the deleterious effects of the dairy? Dairy products are not just associated with getting prostate cancer, but also dying from prostate cancer. Men diagnosed with prostate cancer who then ate more dairy tended to die sooner. And, “[b]oth low-fat and high-fat dairy consumption were…associated with an increased risk of [a] 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. Maybe that’s because they just used isolated soy components rather than a whole soy food. “Taking the whole food approach may be more efficacious.” It’s hard to do controlled studies with whole foods, though; I mean, you can make fake pills, but how do you give people placebo tofu?

Based on all these studies, the results Ornish got were probably more than just the soy. Similarly, the low prostate cancer rates in Asia are probably more than just the soy, since the lowest rates are also found in parts of Africa, and I don’t think they’re eating a lot of tofu in Africa. Indeed, in a 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. And so, the protection associated with plant-based diets may be due to eating a variety of healthy foods. 

To see any graphs, charts, graphics, images, or studies mentioned here, please go to the Nutrition Facts podcast landing page.  There, you’ll find all the detailed information you need plus links to all the sources we cite for each of these topics.

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Thanks for listening to Nutrition Facts. I’m Dr. Michael Greger.

This is just an approximation of the audio content, contributed by Allyson Burnett.