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:

Should We Increase Our Protein Intake After Age 65?

A study that purported to show that diets high in meat, eggs, and dairy could be as harmful to health as smoking supposedly suggested that “[p]eople under 65 who eat a lot of meat, eggs, and dairy are four times as likely to die from cancer or diabetes.” But if you look at the actual study, you’ll see that’s simply not true: Those eating a lot of animal protein didn’t have four times more risk of dying from diabetes—they had 73 times the risk. Even those in the moderate protein group, who got 10 to 19 percent of calories from protein, had about 23 times the risk of dying of diabetes compared to those consuming the recommended amount of protein, which comes out to be about 6 to 10 percent of calories from protein, around 50 grams a day.

So, the so-called low protein intake is actually the recommended protein intake, associated with a major reduction in cancer and overall mortality in middle age, under age 65, but not necessarily in older populations. When it comes to diabetes deaths, lower overall protein intake is associated with a longer life at all ages. However, for cancer, it seems to flip around age 65. I discuss this in my video Increasing Protein Intake After Age 65.

“These results suggest that low protein intake during middle age followed by moderate to high protein consumption in old adults may optimize healthspan and longevity.” Some have suggested that the standard daily allowance for protein, which is 0.8 grams of daily protein for every healthy kilogram of body weight, may be fine for most, but perhaps older people require more. The study upon which the recommended daily allowance (RDA) was based indicated that, though there was a suggestion that the “elderly may have a somewhat higher requirement, there is not enough evidence to make different recommendations.” The definitive study was published in 2008 and found no difference in protein requirements between young and old. The same RDA should be adequate for the elderly. However, adequate intake is not necessarily optimal intake. The protein requirement “studies have not addressed the possibility that protein intake well above the RDA could prove beneficial,” or so suggests a member of the Whey Protein Advisory Panel for the National Dairy Council and a consultant for the National Cattlemen’s Beef Association.

A study followed sedentary individuals over the age of 65 for 12 years and found they lose about one percent of their muscle mass every year. If you force people to lie in bed for days at a time, anyone would lose muscle mass, but older adults on bedrest may lose muscle mass six times faster than young people also on bedrest. So, it’s use it or lose it for everyone, but the elderly appear to lose muscle mass faster, so they better use it. The good news is that in contrast to the 12-year U.S. study, a similar study in Japan found that the “[a]ge-related decreases in muscle mass were trivial.” Why the difference? It turns out that in the Japanese study, “the participants were informed about the results of their muscle strength, [so] they often tried to improve it by training before the next examination.” This was especially true among the men , who got so competitive their muscle mass increased with age, which shows that the loss of muscle mass with age is not inevitable—you just have to put in some effort. And, research reveals that adding protein doesn’t seem to help. Indeed, adding more egg whites to the diet didn’t influence the muscle responses to resistance training, and that was based on studies funded by the American Egg Board itself. Even the National Dairy Council couldn’t spin it: Evidently, strength “training-induced improvements in body composition, muscle strength and size, and physical functioning are not enhanced when older people…increase their protein intake by either increasing the ingestion of higher-protein foods or consuming protein-enriched nutritional supplements.”

Is there anything we can do diet-wise to protect our aging muscles? Eat vegetables. Consuming recommended levels of vegetables was associated with basically cutting in half the odds of low muscle mass. Why? “[T]he alkalizing effects of vegetables may neutralize the mild metabolic acidosis” that occurs with age, when that little extra acid in our body facilitates the breakdown of muscle. I’ve discussed before how “[m]uscle wasting appears to be an adaptive response to acidosis.” (See my video Testing Your Diet with Pee and Purple Cabbage for more on this.) We appear to get a chronic low-grade acidosis with advancing age because our kidney function starts to decline and because we may be eating an acid-promoting diet, which means a diet high in fish, pork, chicken, and cheese, and low in fruits and vegetables. Beans and other legumes are the only major sources of protein that are alkaline instead of acid-forming. And indeed, a more plant-based diet—that is, a more alkaline diet—was found to be positively associated with muscle mass in women aged 18 to 79.

So, if we are going to increase our protein consumption after age 65, it would preferably be plant-based proteins to protect us from frailty. No matter how old we are, a diet that emphasizes plant-based nutrition “is likely to maximize health benefits in all age groups.”


What was that about a study that purported to show that diets high in meat, eggs, and dairy could be as harmful to health as smoking? See my video Animal Protein Compared to Cigarette Smoking.

Protein is so misunderstood. For more on the optimal amount of protein, see Do Vegetarians Get Enough Protein? and The Great Protein Fiasco.

Interested in learning more about the optimal source of protein? See:

What about the rumors that plant protein is incomplete? See The Protein Combining Myth.

For information on buffering the acid in our blood, see Testing Your Diet with Pee and Purple Cabbage.

And, for more on acid/base balance, 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, year-in-review presentations:

Dialing Down the Grim Reaper Gene

Only about 1 in 10,000 people live to be a 100 years old. What’s their secret? I discuss this in my video Animal Protein Compared to Cigarette Smoking.

In 1993, a major breakthrough in longevity research was published about a single genetic mutation that doubled the lifespan of a tiny roundworm. Instead of all worms being dead by 30 days, the mutants lived 60 days or longer. This lifespan extension was “the largest yet reported in any organism.” This methuselah worm, a “medical marvel,” is “the equivalent of a healthy 200-year-old human.” All because of a single mutation? That shouldn’t happen. Presumably, aging is caused by multiple processes, affected by many genes. How could knocking out a single gene double lifespan?

What is this aging gene—a gene that so speeds up aging that if it’s knocked out, the animals live twice as long? It’s been called the Grim Reaper gene and is the worm equivalent of the human insulin-like growth factor 1 (IGF-1) receptor. Mutations of that same receptor in humans may help explain why some people live to be a hundred and other people don’t.

So, is it just the luck of the draw whether we got good genes or bad ones? No, we can turn on and off the expression of these genes, depending on what we eat. Years ago I profiled a remarkable series of experiments about IGF-1, a cancer-promoting growth hormone released in excess amounts by our liver when we eat animal protein. Men and women who don’t eat meat, egg white, or dairy proteins have significantly lower levels of IGF-1 circulating within their bodies, and switching people to a plant-based diet can significantly lower IGF-1 levels within just 11 days, markedly improving the ability of women’s bloodstreams to suppress breast cancer cell growth and then kill off breast cancer cells.

Similarly, the blood serum of men on a plant-based diet suppresses prostate cancer cell growth about eight times better than before they changed their diet. However, this dramatic improvement in cancer defenses is abolished if just the amount of IGF-1 banished from their systems as a result of eating and living healthier is added back. This is one way to explain the low rates of cancer among plant-based populations: The drop in animal protein intake leads to a drop in IGF-1, which in turn leads to a drop in cancer growth. The effect is so powerful that Dr. Dean Ornish and colleagues appeared to be able to reverse the progression of early-stage prostate cancer without chemotherapy, surgery, or radiation—just a plant-based diet and lifestyle program.

When we’re kids, we need growth hormones to grow. There’s a rare genetic defect that causes severe IGF-1 deficiency, leading to a type of dwarfism. It also apparently makes you effectively cancer-proof. A study reported not a single death from cancer in about 100 individuals with IGF-1 deficiency. What about 200 individuals? None developed cancer. Most malignant tumors are covered in IGF-1 receptors, but if there’s no IGF-1 around, they may not be able to grow and spread.

This may help explain why lives appear to be cut short by eating low-carb diets. It’s not just any low-carb diet, though. Specifically, low-carb diets based on animal sources appear to be the problem, whereas vegetable-based low-carb diets were associated with a lower risk of death. But low-carb diets are high in animal fat as well as animal protein, so how do we know the saturated animal fat wasn’t killing off people and it had nothing to do with the protein? What we need is a study that follows a few thousand people and their protein intakes for 20 years or so, and sees who lives longest, who gets cancer, and who doesn’t. But, there had never been a study like that…until now.

Six thousand men and women over age 50 from across the United States were followed for 18 years, and those under age 65 with high protein intakes had a 75 percent increase in overall mortality and a fourfold increase in the risk of dying from cancer. Does it matter what type of protein? Yes. “These associations were either abolished or attenuated if the proteins were plant derived,” which makes sense given the higher IGF-1 levels in those eating excess protein.

The sponsoring university sent out a press release with a memorable opening line: “That chicken wing you’re eating could be as deadly as a cigarette.” It explained that “eating a diet rich in animal proteins during middle age makes you four times more likely to die of cancer than someone with a low-protein diet—a mortality risk factor comparable to smoking.” And when they say “low-protein diet,” what they actually mean is getting the recommended amount of protein.

“Almost everyone is going to have a cancer cell or pre-cancer cell in them at some point. The question is: Does it progress?” said one of the lead researchers. That may depend on what we eat.

“[T]he question is not whether a certain diet allows you to do well for three days,” a researcher noted, “but can it help you survive to be 100?” Excessive protein consumption isn’t only “linked to a dramatic rise in cancer mortality, but middle-aged people who eat lots of proteins from animal sources…are also more susceptible to early death in general.” Crucially, the same didn’t apply to plant proteins like beans, and it wasn’t the fat; the animal protein appeared to be the culprit.

What was the response to the revelation that diets high in meat, eggs, and dairy could be as harmful to health as smoking? One nutrition scientist replied that it was potentially dangerous because it could “damage the effectiveness of important public health messages.” Why? Because a smoker might think “why bother quitting smoking if my cheese and ham sandwich is just as bad for me?”

This reminds me of a famous Philip Morris cigarette ad that tried to downplay the risks of smoking by saying that if we think second-hand smoke is bad, increasing the risk of lung cancer 19 percent, drinking one or two glasses of milk every day may be three times as bad with a 62 percent higher risk of lung cancer. What’s more, doubling the risk is frequently cooking with oil, tripling our risk of heart disease is eating non-vegetarian, and multiplying our risk six-fold is eating lots of meat and dairy. So, they conclude, “Let’s keep a sense of perspective.” The ad goes on to say that the risk of cancer from second-hand smoke may be “well below the risk reported…for many everyday items and activities.” So, breathe deep!

That’s like saying we shouldn’t worry about getting stabbed because getting shot is so much worse. Or, if we don’t wear seatbelts, we might as well have unprotected sex. If we go bungee jumping, we might as well disconnect our smoke alarms at home. Two risks don’t make a right.

Of course, you’ll note Philip Morris stopped throwing dairy under the bus once they purchased Kraft Foods.


The IGF-1 story is so pivotal that it’s one of the first video series I ever produced for NutritionFacts.org. I’m so glad I was able to release this long-awaited update. If you want a blast from the past, watch the original series starting with Engineering a Cure.

For more parallels between the tobacco industry and the food industry, see:

What about the mobile phone industry? Does Cell Phone Radiation Cause Cancer?

For more on healthy aging and longevity, see:

It’s important to note the so-called low protein intake is actually the recommended protein intake, which is associated with a major reduction in cancer and overall mortality in middle age, under age 65. But did you notice that it says not among older individuals? All of this is covered in my video Increasing Protein Intake After Age 65.

In health,
Michael Greger, M.D.

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