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Foods for Prostate Cancer Survival
By Neal D. Barnard, M.D.
Many research studies have shown how foods affect the risk of developing prostate cancer. Vegetables and fruits reduce the risk, while dairy products and fatty foods appear to increase it.
But what about after cancer has been diagnosed? Will a change in eating habits help a man beat the disease? More research is needed, but evidence already available suggests that, whatever other treatments a man may undergo, changes in his diet might well save his life.
The first clues that diet could make a big difference in survival emerged from international comparisons in the 1970s. A man in Hong Kong, where diets are rich in rice and vegetables, is half as likely to have cancerous cells in his prostate, compared to a man in Sweden, where diets are high in dairy products and meat. But if cancer happens to strike, a man in Hong Kong is eight times more likely to survive it, compared to his Swedish counterpart.1 In other words, it appears that the same sort of dietary habits that reduce the risk of cancer also slow its progress if it occurs.
Why would diet changes help? One explanation relates to insulin-like growth factor (IGF-I), a substance in the bloodstream that is a powerful stimulus for cancer cell growth. Men following plant-based diets have lower IGF-I levels than other men, while dairy products tend to drive IGF-I levels up. Men following low-fat diets also have slightly lower testosterone and estrogen levels and higher levels of a protein called sex-hormone binding globulin, which binds and temporarily inactivates testosterone and estrogen. The net effect is a drop in the biochemical factors that stimulate cancer growth.
Fat on Trial
The first prospective studies of diet’s potential benefits were purely observational. In 1999, researchers in Québec City reported their findings after following 384 men with prostate cancer over a five-year period. It turned out that those who consumed the most saturated fat—the kind particularly prevalent in meats and dairy products—had three times the risk of dying from the disease, compared to those with the lowest saturated fat intake. Increased risk was also found with higher intakes of total and monounsaturated fat, but these increases were not significant.2 The following year, researchers in Toronto and Vancouver reported the results of a study of 263 men with prostate cancer. After adjustment for clinical stage, tumor grade, and other factors, men who consumed the most monounsaturated fat (the type that is abundant in olive and canola oils) lived longest. Their risk of dying was 70 percent lower, compared to those with the lowest intake of monounsaturates. The study also found increased risk from animal fat and saturated fat intake, although these latter findings were not strong enough to reach statistical significance.3
Testing a Vegan Diet
Dean Ornish, M.D., who had already demonstrated the benefits of a low-fat, vegetarian diet for heart patients (finding that it reversed heart disease in 82 percent of research participants), decided to put a similar program to the test for prostate cancer.4 The 84 volunteers were men with cancer who were able to defer treatment, at least for the moment, because they were keeping a careful watch on their prostate-specific antigen (PSA, an index of cancer spread) levels, a strategy known as “watchful waiting.” Typically, PSA levels slowly rise, and eventually treatment (e.g., surgery) may be required. Dr. Ornish randomly assigned half the men to their usual care (the control group) and the remaining half to a low-fat, vegan diet, along with regular exercise and stress management. In the 42 men in the control group, PSA levels rose over the three-month study period, and 7 required additional treatment. But in the 42 men assigned to the vegan diet and lifestyle intervention, the average PSA level dropped from 6.3 to 5.8, and none required further treatment. These results were presented at the Scientific Conference on Complementary, Alternative, and Integrative Therapies at Harvard University on April 13, 2002.
Using Diet against Recurrent Cancer
Dr. Ornish’s approach is extremely promising for men with early disease. But what about advanced cancer? Evidence suggests that diet changes can still play a vital role. Two studies have used special diets in men who had previously been operated on for prostate cancer but had recurrences of their disease. Using a macrobiotic diet emphasizing whole grains, vegetables, and legumes while avoiding dairy products and most meats, nine men with prostate cancer had an average survival of 228 months, compared to 72 months for a matched group of men using no special diet.5
A study at the University of Massachusetts tested the benefits of a diet change in ten men with prostate cancer that had recurred after surgery. The diet was based on whole grains, legumes, green and yellow vegetables, seeds, soy products, and fruit, and the men were also instructed in stress-reduction techniques. To measure the program’s effect, researchers tracked how long it took for the patients’ PSA levels to double—the longer the PSA doubling time, the slower the cancer is spreading. Before the study began, the average PSA doubling time was 6.5 months. But after four months in the program, it had slowed to 17.7 months, an encouraging finding. In three of the men, PSA levels actually fell.6
An additional survival study is underway at Memorial Sloan-Kettering Cancer Center in New York.7 And at the University of California at Los Angeles, two studies are in progress.8 In the first, men with prostate cancer who have elected for “watchful waiting” are randomly assigned to a “Western diet” or a low-fat, high-fiber diet, and serum growth factors and biomarkers are followed. In the second study, men scheduled for radical prostatectomy are given green tea, black tea, green tea extract, or a control prior to surgery and their prostate tissue is examined for the effects of these treatments. In 2003, an additional pre-prostatectomy study will begin, studying the effect of a low-fat diet.
Cancer-Fighting Power You Can See
Researchers at the University of California at Los Angeles conducted a series of unusual experiments that demonstrate the power of diet and exercise. They drew blood samples from a group of eight men who had been following a low-fat diet and exercising regularly for several years. They also drew blood samples from overweight men who were not following the diet and exercise program. They added portions of each man’s blood serum to test tubes containing standardized prostate cancer cells. Serum from men on the low-fat diet and exercise program slowed cancer cell growth by 49 percent, compared to serum from the other men. How could this be? Differences in testosterone, estrogen, and insulin account for part of the effect, but other changes in the blood exert additional effects the researchers have not yet teased out.9 The research team also found that a man’s serum shows demonstrable cancer-inhibiting power within as little as eleven days after beginning a low-fat diet and exercise regimen.10
The Bottom Line
While more research will be of great value, evidence already suggests that men with prostate cancer—and their families—should be encouraged to adopt a low-fat, vegan diet. By boosting vegetables, fruits, beans, and whole grains and avoiding dairy products, meats, eggs, and fried foods, men are able to take advantage of protective nutrients and avoid cancer-promoting factors.
For more information, we recommend Healthy Eating for Life to Prevent and Treat Cancer, by the PCRM Expert Nutrition Panel with Vesanto Melina, R.D. (John Wiley & Sons, 2002, available through PCRM Marketplace).
In our next issue, we’ll cover dietary factors in breast cancer survival.
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