Eating foods that are rich in soy phytoestrogens may favorably affect blood markers of prostate cancer, reports a study in Urology (2004;64:510–15). Phytoestrogens are plant-derived compounds that can inhibit the body’s production of certain hormones that are linked to cancer development. The best-known phytoestrogens are the isoflavones found in soy foods.
The prostate is a walnut-sized gland that sits in front of the rectum and under the bladder in men. Prostate cancer, the second leading cause of cancer deaths in American men, is the most common internal cancer. The cause is not completely understood, but it is likely due to a combination of advancing age, race, male hormones, genetics, and dietary factors. Prostate cancer is most common in men who are over age 50. Black men have a much higher incidence of the disease than do Asian, Caucasian, and Hispanic men. Men who have a close relative, such as a brother or father, with prostate cancer are more than twice as likely to develop the disease than those who do not. Diets high in animal fat and meat are linked to higher rates of prostate cancer, while fruits and vegetables seem to protect from the disease. The nutrient lycopene, found in high quantities in tomato products, has been shown to decrease the risk of developing prostate cancer. In countries where soy consumption is high, like China and Japan, the rate of prostate cancer is considerably lower than in the US.
Prostate cancer is often not diagnosed until the disease is quite advanced. At these later stages, urinary problems include difficulty stopping and starting the stream of urine, increased frequency of urination, and painful urination. Men with prostate cancer may also have difficulty attaining an erection, and may have blood in their urine. Low back pain can indicate spread of the cancer beyond the prostate to the spine. Treatments for prostate cancer are varied and may include radiation, surgical removal of the prostate, chemotherapy, and therapies aimed at reducing male hormone levels.
A combination of a blood test called prostate specific antigen (PSA), and a rectal examination by a doctor to feel for abnormalities in the prostate, may help detect prostate cancer before any symptoms are noticed. The PSA test is also used to monitor the response of prostate cancer to treatment. PSA levels are correlated with the size of the tumor, in other words, the higher the PSA level, the larger the tumor. Another test called the free PSA level can be used to increase the chance of detecting prostate cancer.
Numerous animal studies have shown soy phytoestrogens to inhibit prostate tumor growth. The new study investigated the effect of a phytoestrogen-rich diet in 28 men with prostate cancer who were to undergo surgical prostate removal. The men were assigned to receive either a soy-based bread containing 50 grams of soy grits or a whole wheat bread (control group). The soy grits provided a total of 117 mg per day of mixed isoflavones. The participants were instructed to eat the bread each day until the day of surgery; the bread was consumed for an average of 24 days. Blood markers of prostate cancer and hormone levels were measured at the beginning of the study and the day before surgery.
There was a significant PSA-level drop in the men eating the soy bread compared with the control group, suggesting a decrease in the size of the tumor. The results of the current study are encouraging; however, until larger studies are conducted, the interpretation of the results should be taken with caution.
By Kimberly Beauchamp, ND
Kimberly Beauchamp, ND, received her bachelor’s degree from the University of Rhode Island and her Doctorate of Naturopathic Medicine from Bastyr University in Kenmore, WA. She is a co-founder and practicing physician at South County Naturopaths, Inc., in Wakefield, RI. Dr. Beauchamp teaches holistic medicine classes and provides consultations focusing on detoxification and whole-foods nutrition.
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