Transcript: Flax Seeds vs. Prostate Cancer
Below is an approximation of this video’s audio content. To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video.
Why is there such a huge disparity in prostate cancer rates? The incidence of the clinically malignant prostate cancer is highest in African-Americans, some 30-fold greater than in Japanese men, and 120 times greater than seen in Chinese men in Shanghai.
Well, in general terms, the Western diet is one in which animal protein and fat consumption is high, whereas the fiber intake is low. In contrast, the proportion of the total caloric intake from animal fat in the more vegetarian-style Oriental diet is low, and the fiber content is higher.
So, maybe diet is playing a role in some of these diseases. But these healthier diets are not just low in animal proteins and fat, and high in starch and fiber—they are also rich in weak plant estrogens, of which there are two types.
We hear a lot about the soy isoflavones, but less about the other group, lignans. This study found higher levels of lignans in the prostate fluids of men in countries with relatively low rates of prostate cancer, and in vitro studies showed lignans can slow the growth of prostate cancer cells in a petri dish. So, a pilot study was performed on flax seed supplementation in men with prostate cancer, before surgery.
Why flax seeds? Because, while lignans are found throughout the plant kingdom, flax has up to 800 times more than any other food. So, they took a bunch of men with prostate cancer about a month before they were scheduled for surgery to get their prostates removed, and started them on a relatively low fat diet, with three tablespoons a day of ground flax seed, to see what effect that might have on the growth of their tumors.
Though they were skeptical that they would observe any differences in tumor biology in the diet-treated patients with such a short-term dietary intervention, they found significantly lower cancer proliferation rates, and significantly higher rates of cancer cell death. That was compared to so-called historical controls, meaning compared to what kind of growth one typically sees in their situation—not to actual, randomized, control group.
But, a few years later, a study was published in which men were their own controls. These were men who just got their prostates biopsied, and were scheduled to get repeat biopsies in six months. So they did the same thing. After the first biopsy, they reduced the fat in their diet, and put them on ground flax seeds to see if it made their repeat biopsy look any different. These were men with what’s called PIN, which is like the prostate equivalent of ductal carcinoma in situ in the breast—precancerous changes. That’s why they were getting repeat biopsies, to make sure it wasn’t spreading. And this is what they found. Significant drop in PSA levels (which is a biomarker of prostate cell growth); drop in cholesterol (which is what one would expect with a lower-fat diet, and all that extra fiber); and, the most important, a significant decrease in the cellular proliferation rate.
In fact, in two of the men, their PSA levels dropped so much they didn’t even have to go through with the second biopsy. There hasn’t been much research on this kind of prostatic hyperplasia, with only four epidemiologic studies reported at the time. They yielded varying findings, with increased risk associated with higher energy, protein, and animal product intake, and decreased risk related to the consumption of alcohol, fruit, and green and yellow vegetables—in sum, a low-fat, plant-based diet, high in phytoestrogens.
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