OSU scientists study soy and tomato diet in prostate cancer
COLUMBUS, Ohio - Scientists are watching closely to see if men are willing to make significant changes in their diet to help them fight prostate cancer.
The research projects, under the direction of Dr. Steven Clinton, leader of the Prostate and Genitourinary Oncology Research Group at The Ohio State University Comprehensive Cancer Center, will alter the dietary habits of two groups of men - those who are newly diagnosed with prostate cancer, and those whose disease has already metastasized, or spread.
Epidemiological studies strongly support the hypothesis that nutrition plays a critical role in the development and spread of prostate cancer. Although most scientists agree that changes in diet may help prevent prostate cancer, few studies have considered how diet may improve the outcome of prostate cancer treatment. These two new studies, designed around the inclusion of soy and tomato products in the diet, seek to investigate this possibility.
Soy contains hormone-like substances Clinton has shown to slow prostate cancer growth in laboratory animals. In addition, Asian men, who consume diets rich in soy along with diets lower in fat, red meats and calories, are known to have the lowest rates of prostate cancer in the world. American men, who generally do not consume significant amounts of soy, and whose diets are low in fruits and vegetables, but rich in fat and calories, have prostate cancer rates that are 10 to 20 times higher. Interestingly, when Asian men migrate to North America and adopt western lifestyle and eating habits, their risk for prostate cancer increases significantly.
A possible role for tomato products in cancer prevention is also becoming an area of active research. Tomatoes contain a vast array of phytochemicals, or plant-derived compounds, but the one that has received the most attention is lycopene, a carotenoid that gives certain foods (watermelon, pink grapefruit) their red color. Lycopene is a potent antioxidant, a substance that may help prevent oxidative damage to cellular DNA - one of the hallmarks of the cancer process. Some studies suggest that men who consistently eat at least five servings of tomatoes or tomato products each week over the decades it takes for a prostate tumor to develop may experience a 30 to 40% lower risk of prostate cancer.
Until now, most dietary interventions have been directed at prostate cancer prevention. The two new trials at Ohio State are aimed at altering the course of prostate cancer that has already been diagnosed.
"Our ultimate goal is to improve survival and enhance the benefits of therapy. These studies are among the first to bring intensive dietary modification into the treatment phase of prostate cancer," says Clinton.
One study will be limited to men who have just been diagnosed with prostate cancer and who have chosen to undergo surgery to remove the prostate, a procedure called a prostatectomy. While preparing for surgery, all men will be provided with dietary counseling designed to enhance the intake of fruits and vegetables, whole grains, and fiber while reducing the intake of fat and calories. In addition, men will be assigned to one of four groups and asked to consume a soy product, tomato juice, tomato sauce, or tomato soup daily until surgery. The carefully designed soy protein extract may be mixed with milk, juice, water or any other beverage. Scientists will examine how the dietary interventions influence hormonal changes in the blood and urine that may influence the prostate cancer, and also evaluate prostate tissue removed during surgery to identify any changes that may be related to dietary intervention.
The second study is for men with advanced prostate cancer. "We are looking for men that have already had surgery, radiation, or even hormone therapy, but who are now experiencing a rise in their PSA, indicating the treatment has not been totally effective," says Clinton. "This is a very important group of men who are highly motivated to do whatever they can to improve their survival, but may not be experiencing any symptoms and who do not yet wish to start aggressive therapies, such as chemotherapy, that can have side-effects."
Initially, all participants will be advised to follow a healthy diet and exercise program tailored to their needs. Each participant will then be assigned to either four weeks of a diet rich in tomato products or a diet containing the soy supplement. After the initial four weeks, men will then consume both the soy and the tomato additions for another four weeks. Scientists will examine a number of blood and urine biomarkers before intervention and at several intervals after the special diets begin.
"So far, we are seeing rapid and dramatic improvement in blood cholesterol and l blood pressure, and many men have lost 20 to 30 pounds in weight," says Elizabeth Miller, MS, RD, the study dietician.
Investigators will need to study 40 men before they can accurately assess how the special diets may influence the growth of prostate cancer.
"Men with prostate cancer are generally very motivated," says Clinton, "and if the intervention is a dietary change with little risk, it's very attractive. We've been astounded at how well they are making the changes - with very modest effort on our part."
Clinton says many men with prostate cancer are coming into his clinics already consuming a wide variety of supplements and alternative medicines. "We want to be able to tell men for certain which dietary changes are helpful, which ones do nothing. Right now, physicians and patients are just guessing, " says Clinton.
The Arthur G. James Cancer Hospital and Richard J. Solove Research Institute, part of the Comprehensive Cancer Center at The Ohio State University, is the only free-standing cancer hospital in the Midwest. It is a national and international leader in translational research and clinical care, and one of the charter members of the National Comprehensive Cancer Network. It has consistently been ranked one of the nation's best hospitals by U.S. News and World Report.