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Last Updated: 03/29/13

Tomato and Soy Combination Studied for Prostate Cancer Prevention

Center to Reduce Cancer Health Disparities

Krystle Zuniga, a Ph.D. candidate at University of Illinois at Urbana-Champaign (UI-UC), has always been interested in nutrition and learning how various whole foods can have an impact on cancer prevention.

Ms. Zuniga is a recipient of an NCI Ruth L. Kirschstein National Research Service Award* for Individual Pre-doctoral Fellowships to Promote Diversity in Health-Related Research (F31), which is a component of the Continuing Umbrella of Research Experiences (CURE) program at NCI. This fellowship provides Ms. Zuniga with funding support to complete her Ph.D. training in Nutritional Science at the UI-UC and to pursue her goal of becoming a translational researcher in the field of diet and cancer.

In her predoctoral training, Ms. Zuniga – under the mentoring of Steven Clinton, M.D., Ph.D., at The Ohio State University (OSU) – investigated the bioavailability of soy-based compounds, such as isoflavones, and tomato phytochemicals, such as carotenoids, in animal models. Her research on the combination of these foods in rats for prevention of prostate cancer led to Ms. Zuniga’s first peer-reviewed publication**. She was also excited to work with clinical collaborators at OSU “who are trying to look at the combination of soy and tomato products in human clinical trials,” she recalled. “Then we really became interested in finding the optimal combination of those foods for cancer prevention.”

Ms. Zuniga is currently pursuing her interest in research to quantitatively define and understand the mechanisms by which consumption of soy or tomato products, alone or together, may reduce the risk of prostate cancer. “The objective is to investigate the effects of soy germ- and/or tomato powder-containing diets on the progression of prostate cancer in the TRAMP (Transgenic Adenocarcinoma of Mouse Prostate) model,” she noted.

Based on findings from her previous animal study, Ms. Zuniga hypothesized that combining soy and tomato may not be as effective in preventing cancer as are diets that used soy or tomato alone. “We found less carotenoid accumulation in the prostate, liver, and other organs in the rats that received both tomato and soy,” she said. “So we were worried there was a negative interaction of the two foods in the animals and that less of the compounds were getting into the tissues of interest and maybe making the combination less protective.”

Although her current study in the TRAMP model found similarly lower levels of carotenoids in tissues from the combination diet, nonetheless, the mice who ate both soy and tomato powder did better in terms of the progression of prostate cancer, Ms. Zuniga reported, compared with mice who were fed only one of the foods, and compared to the control group who ate neither. She plans to publish her findings in the near future.

“I think it’s exciting that this intervention is able to have this much of an effect in a very aggressive model of prostate cancer in mice,” Ms. Zuniga noted. Because most prostate cancers in men are slow growing, “the type of effect such a dietary combination could have in humans could be pretty significant as well.” The use of a whole-foods approach for cancer prevention also avoids many of the safety concerns from traditional chemoprevention by using large doses of single compounds extracted from plants and other sources, she said.

The NCI fellowship grant “has been helpful to my career,” Ms. Zuniga commented. “I was really excited to get funded to do this type of project in nutrition and cancer prevention.”

* Grant number: 1F31CA153804-01A1

** Zuniga K., & Erdman J. (2011). Combined consumption of soy germ and tomato powders results in altered isoflavone and carotenoid bioavailability in rats. Journal of Agricultural and Food Chemistry, 59, 5335-41.