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The US Food and Drug Administration is explaining its stance on the cancer-fighting potential of tomatoes and lycopene, the compound that gives tomatoes their red color. The agency says there is "no credible evidence" that lycopene reduces the risk of cancer, and only "very limited credible evidence" that tomatoes and tomato sauce do.

That doesn't mean you should take tomatoes off your shopping list, though. The American Cancer Society still recommends eating a wide variety of colorful fruits and vegetables every day, and tomatoes definitely fit that bill, says Colleen Doyle, MS, RD, American Cancer Society director of nutrition and physical activity.

Rather, the FDA judgments affect the cancer-related claims that food or supplement companies can put on their products. None are allowed for lycopene, and only a few carefully worded claims are allowed for tomatoes and tomato products.

In a report published in this week's Journal of the National Cancer Institute, agency scientists describe how they came to their conclusions.

The FDA review was prompted by requests the agency received in 2004 from companies that wanted to put cancer-related health claims on their tomato or lycopene products. The companies asked the FDA to review the evidence linking these compounds to lower risks of several cancers including prostate, lung, colorectal, stomach, breast, cervical, endometrial, ovarian, and pancreatic cancer.

Numerous studies have examined the issue. The FDA considered scores of these studies -- and rejected most of them.

The rejected studies were not included in the evidence review because the FDA found flaws in the design or because the studies did not provide enough information for FDA scientists to draw conclusions.

Of 81 studies of lycopene and cancer, all were excluded from the review for these reasons. One major problem the FDA cited: In studies of diet, it's too difficult to determine the effect of a single nutrient -- in this case lycopene -- when so many others may also be at play. As a result, the agency determined there was no credible evidence to support a link between lycopene in any form (as a supplement or as part of food) and a lower risk of any of the cancers it considered.

Of 64 studies on tomatoes or tomato products and cancer, only 39 were deemed strong enough to be included in the FDA review. The agency found no credible evidence, based on these studies, to support the idea that tomatoes or tomato products lower the risk of lung, breast, colorectal, endometrial, or cervical cancer.

The FDA found what it called "very limited credible evidence" linking these foods to lower risk of pancreatic, ovarian, and stomach cancer. The evidence was so sparse, however, that the agency says it's unlikely that eating tomatoes can lower the risk of ovarian and stomach cancer, and highly unlikely that the food affects pancreatic cancer risk.

The evidence for prostate cancer was slightly better, but still "limited," the JNCI report says. The agency identified 2 large, prospective studies that did show a reduced risk, but also several smaller studies that had mixed results. The agency therefore decided that there is a "very low level of comfort that a relationship exists between the consumption of tomatoes and/or tomato sauce and prostate cancer risk."

In an editorial published along with the report, the lead author of one of those positive prostate cancer studies says the FDA's conclusions shouldn't discourage future research into the prostate cancer-preventing potential of tomatoes and lycopene.

Edward Giovannucci, MD, ScD, of the Harvard School of Public Health, says the FDA's review could not account for the effect of PSA testing on prostate cancer detection rates, or for potentially protective effects tomatoes and lycopene may have on more advanced forms of prostate cancer.

"This area of research remains promising," he writes.

The FDA's report highlights the fact that a single food isn't likely to be a magic bullet against cancer, says Doyle.

"What has been linked to a reduced risk [of cancer] is an overall healthy diet that includes a variety of fruits and vegetables," she stresses.

So if you like tomatoes, dig in.

"Choose fruits and vegetables with the most color, like broccoli, tomatoes, cantaloupe, and deep green leafy vegetables like kale," Doyle advises. "These are packed with nutrients and other plant chemicals that have been associated with a lower risk of cancer and other diseases."

Another reason to keep the crisper stocked: Fruits and veggies are low-cal, so eating them won't add inches to your waistline. Keeping your weight in check is one of the most important ways to lower your cancer risk, Doyle says.

Citation: "The US Food and Drug Administration's Evidence-Based Review for Qualified Health Claims: Tomatoes, Lycopene, and Cancer" Published in the July 18, 2007 Journal of the National Cancer Institute (Vol. 99, No. 14: 1074-1085). First author: Claudine J. Kavanaugh, PhD, MPH, RD, Center for Food Safety and Nutrition, US Food and Drug Administration.

"Does Prostate-Specific Antigen Screening Influence the Results of Studies of Tomatoes, Lycopene, and Prostate Cancer Risk" Published in the July 18, 2007, Journal of the National Cancer Institute (Vol. 99, No. 14: 1060-1062). First author: Edward Giovannucci, MD, ScD, Harvard School of Public Health.