How Tomatoes Flunked the FDA's Anticancer Test

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COLLEGE PARK, Md. -- The FDA won't rule out the possibility that tomatoes are cancer-fighters, but it considers the evidence supporting that claim to be exceedingly flimsy.

COLLEGE PARK, Md., July 10 -- The FDA won't rule out the possibility that tomatoes are cancer-fighters, but it considers the evidence supporting that claim to be exceedingly flimsy.

Eighteen months after the agency refused a request from food companies to allow them to make unfettered claims that both fresh and cooked tomatoes have anti-malignancy properties, and that lycopene, the anti-oxidant in the fruit, is responsible, the FDA has explained its thinking.

If granted, food companies would have been able to advertise that everything from the tomato sauce on pizza to lycopene capsules from a health food store prevented a range of cancers, Claudine Kavanaugh, Ph.D., of the FDA's Center for Food Safety and Applied Nutrition here, and colleagues wrote in the July 10 issue of the Journal of the National Cancer Institute.

But after a painstaking analysis of 145 studies, the agency concluded there's no scientific evidence of any cancer-fighting benefit from lycopene and only limited evidence for any benefit from tomatoes themselves. (See FDA Tomato Ruling May Make Pizza a Health Food)

All of the 81 observational studies of lycopene and cancer were rejected as failing to meet the scientific standards for a claim of a cancer prevention benefit, Dr. Kavanaugh and colleagues said.

But tomatoes themselves, whether fresh or cooked, fared better. Of the 64 studies of tomatoes and various forms of cancer, only 25 were rejected outright.

And, on the basis of the review of the remaining 39, Dr. Kavanaugh and colleagues said, food companies were allowed to make "qualified claims" that tomatoes might reduce the risk of prostate, gastric, ovarian, and pancreatic cancer.

But any claims had to include the FDA's own view of the evidence:

  • For prostate cancer, there was "little scientific evidence" supporting an anti-cancer benefit.
  • For gastric cancer, "FDA concludes that it is unlikely that tomatoes reduce the risk."
  • For ovarian cancer, "it is highly uncertain that tomato sauce reduces the risk."
  • For pancreatic cancer, "FDA concludes that it is highly unlikely that tomatoes reduce the risk."

For all other malignancies that were studied - including breast, lung, and cervical cancer -- the FDA concluded there wasn't enough credible evidence to allow any form of health claim, no matter how qualified.

The process was limited by the small number of high-quality studies, said Paul Coates, Ph.D., of the NIH in an accompanying editorial, and the results are likely to be difficult to communicate properly to the public.

But neither problem "diminishes the importance of using evidence-based review principles to evaluate important diet-health relationships," Dr. Coates said.

He added that one advantage of an evidence-based review system is that the issue can be re-opened if new data become available.

In another editorial, Edward Giovannucci, M.D., Sc.D., of the Harvard School of Public Health, argued that the widespread use of prostate-specific antigen testing might be skewing the data concerning prostate cancer and tomatoes.

In places where PSA tests are used widely, Dr. Giovannucci argued, the rate of prostate cancer increases, as more small cancers - including many that are not clinically important - are found.

If occurrence is used as an endpoint, he said, any beneficial effect of either lycopene or tomatoes themselves might be overwhelmed by the increased rate of disease.

He noted that studies supporting a benefit for lycopene or tomatoes were either done in the U.S. before widespread PSA testing or more recently in places where PSA tests are still not widely used.

"Although it may be premature to espouse increased consumption of tomato sauce or lycopene for prostate cancer prevention, this area of research remains promising," he said.

Dr. Giovannucci was lead author of a 2002 prospective study in the Journal of the National Cancer Institute on tomato products, lycopene, and prostate cancer risk.