John Erdman a University of Illinois professor of food science and nutrition, said that for their study they used mice that were genetically engineered to develop an aggressive form of prostate cancer
He said that even so, half the animals that consumed tomato and soy had no cancerous lesions in the prostate at study's end.
However, all the mice in the control group-no soy, no tomato-developed the disease, he said.
From the time the mice were 4 to 18 weeks old, the animals were fed one of four diets, (1) 10 percent whole tomato powder; (2) 2 percent soy germ; (3) tomato powder plus soy germ; and (4) a control group that ate neither tomato nor soy.
Erdman said that the 4- to 18-week time frame modelled an early and lifelong exposure to the bioactive components in these foods.
He said that eating tomato, soy, and the combination all significantly reduced prostate cancer incidence. But the combination gave us the best results.
Erdman asserted that 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.
Erdman noted that 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.
Krystle Zuniga, co-author of the paper, said that the results of the mouse study suggests that three to four servings of tomato products per week and one to two servings of soy foods daily could protect against prostate cancer.
Erdman said that it's better to eat a whole tomato than to take a lycopene supplement and it's better to drink soy milk than to take soy isoflavones.
He said that when people eat whole foods, they expose themselves to the entire array of cancer-fighting, bioactive components in these foods.
He added that of the isoflavones, genistein gets most of the attention. But soy germ is very high in the other isoflavones, daidzein and glycitein, and low in genistein.