URBANA, Ill. — Tomatoes and soy foods may be more effective
in preventing prostate cancer when they are eaten together than when either is
eaten alone, according to a University of Illinois study.
“In our study, we used mice that were genetically engineered
to develop an aggressive form of prostate cancer,” said John Erdman, a U of I
professor of food science and nutrition. “Even so, half the animals that had
consumed tomato and soy had no cancerous lesions in the prostate at study’s end.
All mice in the control group — no soy, no tomato — developed the
From the time they were 4 to 18 weeks old, the animals were
fed one of four diets: 10 percent whole tomato powder; 2 percent soy germ;
tomato powder plus soy germ; and a control group that ate neither tomato nor
The four- to 18-week time frame modeled an early and
lifelong exposure to the bioactive components in these foods, Erdman said.
“Eating tomato, soy and the combination all significantly
reduced prostate cancer incidence,” he said. “But the combination gave us the
best results. Only 45 percent of mice fed both foods developed the disease
compared to 61 percent in the tomato group, and 66 percent in the soy group.”
Prostate cancer is the most frequently diagnosed cancer in
men, but the disease has nearly a 100 percent survival rate if it’s caught
early. In older men, it often is a slow-growing cancer, and these men often
choose watchful waiting over radiation and surgical treatments that have
unwelcome side effects, said Krystle Zuniga, co-author of the paper.
Soy isoflavone serum and prostate levels in the mice are
similar to those found in Asian men who consume one to two servings of soy
daily. In countries where soy is eaten regularly, prostate cancer occurs at
significantly lower levels, Erdman noted.
How much soy and tomato should a 55-year-old man concerned
about prostate health eat in order to receive these benefits?
“The results of the mouse study suggest that three to four
servings of tomato products per week and one to two servings of soy foods daily
could protect against prostate cancer,” Zuniga said.
According to the scientists, these findings reinforce the
recommendation that we should all eat a wide variety of whole fruits and
“It’s better to eat a whole tomato than to take a lycopene
supplement,” Erdman said. “It’s better to drink soy milk than to take soy
isoflavones. When you eat whole foods, you expose yourself to the entire array
of cancer-fighting, bioactive components in these foods.”
The researcher’s whole-food recommendation is bolstered by
the way soy germ performed in this study. He noted that soy germ has a very
different isoflavone profile than the rest of the soybean.
“Of the isoflavones, genistein gets most of the attention,”
he said. “But soy germ is very high in the other isoflavones, daidzein and
glycitein, and low in genistein.”
It was interesting for the scientists to see that the soy
product they used, although low in genistein, was still very effective at
reducing cancer incidence, Erdman added.
“The interactions of dietary tomato powder and soy germ on
prostate carcinogenesis in the TRAMP model” has been published online in Cancer
Prevention Research and is available at
Zuniga and Erdman of the U of I Division of Nutritional
Sciences and Steven K. Clinton of Ohio State University are co-authors of the
article. Funding was provided by the National Cancer Institute, National
Institutes of Health.