For the past few years, preliminary studies of tomatoes and lycopene -- the antioxidant substance that makes them red -- suggested that the fruit and its extracts may reduce the risk of cancer.
Consumers took note, and lycopene become the fourth best-selling supplement in the United States.
But now a review by researchers from the U.S. Food and Drug Administration published in the current issue of the Journal of the National Cancer Institute has found that there is very little scientific evidence for the anti-cancer properties of either tomatoes or lycopene.
"We wrote this article, based on the data from 2005, to give the scientific community a window into how we make regulatory decisions," said the study's lead author Claudine Kavanaugh, a researcher at the Center for Food Safety and Applied Nutrition.
"But we are also trying to help the consumer, to give consumers more information about the level of science that supports health claims."
The review examined 64 separate studies that took place from 1989 to 2005.
The FDA team found that tomatoes had no effect on the risk of lung, colorectal, breast, cervical or endometrial cancer.
They did find some "very limited" evidence that tomatoes -- but not lycopene alone -- slightly reduced the risk of certain cancers, including prostate, ovarian, gastric and pancreatic cancer.
And based on those slim scientific credentials, the FDA will continue to allow companies that market tomato products to advertise some possible cancer risk reduction.
"Basically, if there is a certain amount of data, we are required by law to let companies make qualified health claims on their packaging," said Kavanaugh.
Some Call Tomato Health Claims Rotten
But even though companies can still legally label their products as having cancer-reducing agents, some public interest groups say this is hypocritical.
"Studies show that consumers are confused by such messages, which obfuscate the consensus-based advice to eat more fruits, vegetables and whole grains, and to cut back on saturated fats, trans fats, sodium and sugar," said Bruce Silverglade, director of legal affairs at the Center for Science in the Public Interest.
"The FDA should keep dietary advice simple, and not permit health claims for foods like tomatoes and tomato sauce when the agency itself has found that the evidence is weak."
Though researchers are still unclear on exactly why lycopene does not appear to reduce the risk of cancer alone, one possibility is that it has to work in tandem with other substances in tomatoes to be beneficial.
"Most whole foods -- especially whole grains, soy and beans -- are a complex package of nutrients, fibers, phytochemicals, minerals and some have phytosterols and antinutrients," said Dr. James Anderson, professor of medicine and clinical nutrition at the University of Kentucky.
"Working synergistically, these components may offer benefits not seen with isolated ingredients."
Others agree that the total nutritional value food is more than just the sum of its parts.
"Even if lycopene is the key nutrient in the tomato, it may need the other compounds in the tomato to do its best work," said Keith Ayoob, associate professor of pediatrics at the Albert Einstein College of Medicine.
"This isn't exclusive to tomatoes. Better preliminary results with weight loss were found with dairy calcium than with calcium supplements, and the list could go on."
Absence of Proof, or Proof of Absence?
But while the latest round of research delivers a blow to lycopene, most agree that more studies are needed.
"Nutrition science is constantly evolving," said Ayoob. "Studies aren't perfect, and no one study is ideal, so there have to be many. So many of the epidemiological studies are treated as gospel, and that's wrong."
Others point out that this was a review of previous studies, not a large, randomized clinical trial, which could have yielded stronger results.
"It reaffirms what we keep learning over and over again," said Dr. David Katz, director of the Prevention Research Center at Yale University School of Medicine.
"There is no silver bullet in food. Dietary pattern influences health very powerfully. But that power does not tend to reside in a single food, and certainly not in a single nutrient. Lycopene joins the ranks of vitamin C, beta carotene, and vitamin E in this regard."
Meanwhile, Katz says there are many common-sense ways to take care of yourself and reduce your risk of cancer.
"Eat well overall, be active, don't smoke, control your weight," he said. "The best defense we know against cancer is taking good care of yourself."
He added: "Tomatoes have a role in that, but just a supporting role. They are not a stand out star; this show requires an ensemble cast."