Soy Bread Studied in Men with Prostate Cancer

NCI CAM Annual Report-FY10

Compared with men in the United States, men living in many Asian nations have a lower risk of prostate cancer. “If you look at what factors may contribute to the differences in risk, one of the many variables that jumps out is the much greater consumption of soy in Asia,” said Steven Clinton, M.D., Ph.D., a professor of Medical Oncology at Ohio State University (OSU), who studies the role of dietary factors in prostate and other cancers.

Research in Dr. Clinton’s laboratory and else­where – including studies in mouse models of prostate cancer – have shown that certain phytochemicals (chemicals that are found in plants) in soy have potential anti-prostate-cancer properties. However, the ability of soy to help prevent or treat prostate cancer in men remains unproven.

One of the challenges researchers face in study­ing this question is coming up with a conve­nient – and tasty – way to incorporate adequate, well-defined amounts of soy phytochemicals into the typical Western diet. With support from NCI*, Yael Vodovotz, Ph.D., an associate professor in OSU’s Department of Food Science and Technology, is collaborating with Dr. Clinton to compare two types of soy bread that the researchers developed for that purpose. The soy bread “provides in two slices a dose of soy phytochemicals that would be similar to that consumed daily by many Asian popula­tions,” said Dr. Clinton.

The researchers are focusing on soy bread as a so-called functional food (foods that have potential health benefits, beyond just basic nutrition), rather than giving people individual soy phytochemicals, and in particular, soy compounds known as isoflavones. “The idea is that not only the isoflavones, but also the other components of soy may be very critical” for the biological effects in humans, Dr. Vodovotz said. She said that using soy bread as a “phytochemi­cal delivery system” allows researchers to create a consistent product, yet provide a complex variety of soy components.

The OSU researchers are conducting a small clinical study to compare two types of soy bread as a source of phytochemicals in the diet. Both varieties contain isoflavones, but one of the breads includes an enzyme that yields twice as much of an altered form of isoflavone, known as the aglycone form, Dr. Vodovotz explained. The aglycone form is believed to be more biologi­cally active and more readily absorbed from the digestion into the bloodstream than unaltered forms of isoflavones.

The 40 men in the study all had active prostate cancer and rising prostate specific antigen (PSA) -a biological marker of prostate cancer- levels but were not undergoing active therapy during the 20-week study period. For the first 8 weeks, half of the men ate three slices per day of the regular soy bread, while the other half ate three slices daily of the aglycone-enriched bread. After a 2-week, soy-free period, each study participant ate the other form of soy bread for another 8 weeks.

The researchers found that about 90% of the men could eat the soy breads on a daily basis without any difficulties, while about 5% experi­enced very minor gastrointestinal distress. No other serious problems were observed, Dr. Clinton said. “Overall, the majority of men found the food easily incorporated into the diet, and some men are even purchasing soy bread that is now on the market, while others are making their own soy bread at home,” he noted. “At least a third of the men suggested that we need to improve the product to make it competitive with breads available on the market.”

The researchers are analyzing blood samples from the men and running a range of tests to find out whether the aglycone form of isofla­vones is in fact better absorbed and has a greater effect on various biomarkers that have been linked with anti-cancer activity.

Once the final results are in, the researchers hope to use an optimized form of soy bread in clinical trials that will rigorously test the ability of soy phytochemicals to improve the treatment of prostate cancer or to prevent the disease in men who are considered at high risk. Dr. Vodo­votz commented, “We hope to eventually have the bread in a commercially available form, be­cause if you’re going to recommend something for prostate cancer, it better be available in the marketplace.”