Harvard Men's Health Watch

Medical memo: Food for thought: Tomatoes, broccoli, and prostate cancer

Medical memo

Food for thought: Tomatoes, broccoli, and prostate cancer

Scientists don't know what causes prostate cancer, but they have good reason to think that diet plays an important role. Since obesity increases risk, calories are the biggest culprits. Among specific foods and nutrients, saturated fat from animal sources (especially whole-fat dairy products and red meat) appears to be the major worry. Large amounts of calcium and alpha-linolenic acid (the omega-3 fat in canola oil and flaxseeds) may also increase the risk of aggressive prostate cancer. In contrast, whole grains, fruits and vegetables, fish, selenium, vitamin D, and perhaps vitamin E (in smokers) may decrease risk. Soy products, red wine, and pomegranates have also been touted as possibly protective, but the evidence is far from conclusive.

It will take time for researchers to sort this out. Human biology is complex, and clinical studies are slow and expensive. For example, although the 35,500-person SELECT trial should give us the answers about vitamin E and selenium, results are not expected until 2012. To gain insights at a faster pace, scientists often turn to animal studies. And reports make tomatoes and broccoli look awfully good, at least for rats.

Rodent research

A 2007 experiment was conducted by a team of scientists from the University of Illinois and Ohio State University. The "volunteers" were 206 male rats. The animals were divided into six groups that were fed diets containing (1) 10% tomato plus 10% broccoli, (2) 5% tomato plus 5% broccoli, (3) 10% broccoli, (4) 10% tomato, (5) lycopene powder (an antioxidant found in tomatoes and other foods that's been touted as being good for the prostate), and (6) normal diet. After one month, prostate cancer cells were implanted in each animal. Two additional groups of animals received only the normal rat diet; one of these groups was started on the testosterone-blocking drug finasteride after tumor implantation, and the other underwent surgical castration.

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