Tomato Diet Can't Guarantee Prostate Health: Study

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Stopping progression is crucial. According to Scardino, for those whose disease does progress, the risk of death is much higher -- nearly 50 percent.

"I think it's an important study," Scardino said. That lycopene and bulk carotenoids reduced the risk of progressing to advanced disease without impacting the risk of developing prostate cancer overall, he said, "suggests maybe these micronutrients are not as important in [stopping] carcinogenesis as they are in [slowing] progression of a very small early tumor to one that becomes invasive and larger and develops the ability to metastasize."

"The study provides supportive evidence that lycopene and the carotenoids may have an effect on delaying the progression of prostate cancer, so, from that point of view, it is an interesting study," Scardino added.

But Alan Kristal, associate head of the Cancer Prevention Program at the Fred Hutchinson Cancer Research Center in Seattle, remained more skeptical. Though he called the study "well-executed," Kristal noted, for instance, that the authors were unable to control for prostate-specific antigen (PSA) testing among the men. These blood tests often detect clinically irrelevant tumors, he explained.

"You can never do an observational study of prostate cancer without rigorously controlling for whether or not the person got PSA screening," Kristal said. "The more times you take the test, the more likely you are to get the disease."

He also noted that the finding for lycopene contradicts a report published in May in Cancer Epidemiology Biomarkers and Prevention. That study did account for PSA testing, and it found no effect of lycopene whatsoever on prostate cancer risk -- including the risk of advanced disease.

"To my mind, that study is definitive," said Kristal. "It's a big study, extremely well executed, properly analyzed, and not biased by PSA screening."

A review of lycopene's effect on cancer by the U.S. Food and Drug Administration, published in July in the Journal of the National Cancer Institute, likewise found "no credible evidence to support an association between lycopene intake and a reduced risk of prostate, lung, colorectal, gastric, breast, ovarian, endometrial, or pancreatic cancer and very limited evidence to support an association between tomato consumption and reduced risks of prostate, ovarian, gastric, and pancreatic cancers," according to that study's authors.