Soy and tomato foods are probably better at preventing prostate cancer when eaten in combination than alone, researchers from the University of Illinois reported this week.

John Erdman, professor of food science and nutrition, and colleagues used genetically engineered laboratory mice for their study. They were engineered to develop a fast-progressing aggressive form of prostate cancer.

Half the mice that were give tomato and soy had no cancerous lesions in their prostates at the end of the study, compared to ALL the mice in the control group. The control group were given no soy or tomato.

From the age of 4 to 18 weeks, the mice were divided into four groups:

  • 10% whole tomato powder group
  • 2% soy germ group
  • Tomato combined with soy germ group
  • Control group – their food contained neither tomato no soy foods

Professor Erdman explained that that the time frame – 4 to 18 weeks old – reflects an early and lifelong exposure to the bioactive compounds and/or elements in these foods.

Erdman said:

“Eating tomato, soy, and the combination all significantly reduced prostate cancer incidence. 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.”

A study carried out in 2009 by scientists at the National Cancer Institute and Fred Hutchinson Cancer Research Center and published in Cancer Epidemiology, Biomarkers & Prevention (May 2007 issue) reported that lycopene, an antioxidant predominantly found in tomatoes, does not prevent prostate cancer.

Although prostate cancer is the most commonly diagnosed male cancer, it is almost 100% treatable if diagnosed and dealt with early enough. Among elderly patients diagnosed with the disease, it tends to be a very slow-growing cancer. Doctors usually recommend “watchful waiting” in such cases, rather than surgical procedures and/or radiation therapy, co-author Krystle Zuniga explained.

Previous research had shown that prostate cancer rates are lower in countries where soy is regularly eaten by males. Soy isoflavone serum and prostate levels in laboratory mice are similar to levels found in Asian males who eat one or two servings of soy each day.

Zuniga says that the results of the mouse study suggest a 55-year-old male who wants to reduce his risk of developing prostate cancer should consume:

  • 3 to 4 servings of tomato products per week
  • 1 or 2 servings of soy foods per day

The scientists emphasized that their findings also reinforce the recommendation that people should make sure their diets contain a wide range of whole fruits and vegetables.

Erdman said:

“It’s better to eat a whole tomato than to take a lycopene supplement. 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.”

Erdman added that the nutritional focus should be in the soy germ, which has a completely different isoflavone profile from the rest of the soybean. “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.”

The researchers pointed out that the soy product they used was very low in genistein but still has a powerful cancer-prevention benefit. Genistein is known to target MEK4 in human prostate cancer cells.

Written by Christian Nordqvist