COLUMBUS, Ohio – A tomato a day may help keep prostate cancer at bay -- but a widely used dietary supplement derived from tomatoes may not be sufficient. That's the conclusion of the first animal study comparing the cancer-preventing potential of tomato products to that of lycopene, a substance extracted from tomatoes and taken by many men in hopes of warding off prostate cancer.
Research by scientists at The Ohio State University Comprehensive Cancer Center – Arthur G. James Cancer Hospital and Richard J. Solove Research Institute and their colleagues showed that rats with prostate cancer survived longer when fed a diet that included whole tomato products but not when fed the same diet plus lycopene. The effect was most apparent when the animals' food intake was modestly restricted. The study was published in the Nov. 4 issue of the Journal of the National Cancer Institute.
"Our findings strongly suggest that risks of poor dietary habits cannot be reversed simply by taking a pill," says study co-author Steven K. Clinton, associate professor of hematology and oncology and of human nutrition. "We shouldn't expect easy solutions to complex problems. We must focus more on choosing a variety of healthy foods, exercising and watching our weight."
A number of earlier studies have suggested that eating tomatoes and tomato products such as sauce, paste and soup is associated with a lower prostate-cancer risk. Scientists proposed that lycopene, a potent antioxidant and the substance that makes tomatoes red, gives the fruit its anti-cancer properties.
Clinton and his colleagues first separated 194 rats with prostate cancer into three groups. A control group was fed a balanced diet containing no detectable lycopene. The second group received the control diet plus lycopene, and a third group received the control diet mixed with tomato powder made from tomato paste that included seeds and skins.
Additionally, each group was subdivided into an energy-restricted group and an energy-unrestricted group. Animals in the unrestricted group received as much food as they wanted; energy-restricted animals received 20 percent less food than the unrestricted group. The experiment lasted about 14 months.
Rats in the tomato-fed, energy-unrestricted group showed a longer prostate-cancer free survival compared to controls. Their risk of dying from prostate cancer dropped by 26 percent. Animals in the tomato-fed, energy-restricted group fared even better, showing a 32 percent drop in risk. No benefit from lycopene alone was seen in either the energy-restricted or unrestricted groups.
"Our study does not say that lycopene is useless," Clinton says. "Instead it suggests that if we want the health benefits of tomatoes, we should eat tomatoes or tomato products and not rely on lycopene supplements alone."
Along with Clinton, John W. Erdman, Jr., professor of nutritional sciences, University of Illinois, Urbana-Champaign; Thomas W.-M. Boileau, post doctoral fellow; Zhiming Liao, research scientist; Sunny Kim, statistician; Stanley A. Lemeshow, professor of public health and director, Biostatistics Program, all from Ohio State, also worked on the project.
Funding from the National Cancer Institute and The Ohio State University Comprehensive Cancer Center supported this research.