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NEWS & VIEWS

TOMATOES BEAT LYCOPENE ALONE FOR PROSTATE CANCER PROTECTION

A recent study suggests whole tomatoes offer better protection from prostate cancer than lycopene supplements alone. The research, published in the Journal of the National Cancer Institute (2003;95:1,578–1,586), found that rats that were fed tomato powder (including seeds and skins) had a lower risk of dying with prostate cancer than rats fed either a control diet or the control diet supplemented with lycopene.

Several epidemiologic studies have suggested that lycopene-rich tomato products have a protective effect against prostate cancer. But the question of whether lycopene acts alone or in concert with other components of tomatoes has been difficult to ascertain.

Researchers from Ohio State University and the University of Illinois, Urbana-Champaign addressed this question with a rat model of prostate carcinogenesis. They randomized 194 male rats treated with the carcinogenic regimen of N-methyl-N-nitrosourea and testosterone into six diet groups. The first three groups had unrestricted access to their food; one group received a control diet, the second and third groups received an otherwise identical diet containing either lycopene (161 mg lycopene/kg diet) or whole tomato powder (13 mg lycopene/kg diet). The other three groups were randomized to the same three food sources, but in addition, their food intake was restricted by 20% (they were fed 80% of the average daily intake of rats in the free-feeding group).

Rats on the free-feeding tomato powder diet had a 26% lower risk of dying with prostate cancer and a 21% lower overall mortality rate compared with animals on the control diet; reductions in disease-specific and overall mortality were statistically significant. By contrast, lycopene supplementation did not significantly affect either outcome. Calorie-restriction significantly reduced prostate cancer-specific mortality (by 32%) but did not significantly affect overall mortality.

"This study suggests we need to put at least as much emphasis into looking at whole foods as cancer preventive agents and not just single substances derived from them," said study coauthor Steven Clinton, MD, PhD, Associate Professor of Hematology and Oncology, and Human Nutrition at Ohio State University.

He also noted that the finding that energy restriction reduces tumor growth supports the recent ACS study published in the New England Journal of Medicine (2003;348:1,625–1,638), which found that obesity is a contributing factor in many cancers, including prostate cancer. "I think what we’re seeing in animals is probably relevant to humans and reaffirms concern about excess caloric intake and lack of exercise that are now really common in our society," Clinton said.

No significant interactions were observed between the effects of food restriction and tomato powder, suggesting the benefit of these two interventions might be additive.

While the findings don’t challenge the view of lycopene as an important compound in prostate cancer prevention, they do suggest it works best in the presence of other compounds found in tomatoes and other foods. "Perhaps there’s been too much emphasis on the reductionist approach that a whole food can be replaced by one component," said Clinton.

Rather, he recommends what the ACS and the National Cancer Institute promote: a varied diet rich in fruits and vegetables, with at least five servings a day. "I try to tell my patients it’s reasonable to consider including tomato products within that recommendation ... epidemiological studies suggest men would do well to eat five to seven servings of tomato products each week."

What kind of tomato product is best has not been firmly established, Clinton noted. "Whole tomatoes and processed - juice, soup, sauce - all can be considered healthy ways to get tomato products," he said. "Right now I’d use the word ‘variety’. "

Whole tomatoes may be a better bet for prostate health than lycopene supplements.

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