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Prostate Cancer: The Role of Tomatoes in Prevention
You know the age-old adage, "an apple a day keeps the doctor away." Well, there may soon be a variation -- "A little tomato sauce a day keeps prostate cancer at bay." Sure, it sounds far-fetched, and the connection needs more research. But scientists are buzzing about a powerful plant chemical found largely in tomatoes and tomato products. It's called lycopene.
What Is Lycopene, and What Foods Contain It?
Lycopene is a carotenoid, a plant substance that gives fruits and vegetables a range of colors -- from yellow to bright red. It's found in tomatoes, dried apricots, pink grapefruit, guava, watermelon, and papaya.
Lycopene is also an antioxidant. Antioxidants are natural agents found in fruits, vegetables, tea, and soy. Scientists believe antioxidants may fight cancer with their ability to combat free radicals. The body normally makes free radicals, which help fight off infections and viruses. But too many of these highly charged little bundles may damage the DNA in cells, which can lead to the growth of cancer cells.
What's the Connection With Prostate Cancer?
Scientists think lycopene may act as a powerful antioxidant and control the spread of tumor cells in the prostate. Elizabeth Johnson, PhD, is a scientist who studies carotenoids and disease. She says, "Of all the carotenoids, or plant pigments, lycopene has the strongest antioxidant activity."
But these theories have yet to be proven. Jin-Rong Zhou, PhD, from Harvard Medical School and the director of the Nutrition Metabolism Laboratory at Beth Israel Deaconess Medical Center in Boston, explains, "Lycopene was originally linked with prostate cancer from population studies. These showed that men who ate more tomatoes and tomato products, such as spaghetti sauce, had lower rates of prostate cancer. Researchers believed lycopene in the tomatoes was the important ingredient. Yet there is no direct evidence of how lycopene works in the prostate tissue. The antioxidant benefit is one idea but not clearly proven."
Tomato Sauce and Tomatoes: Not Created Equal
Johnson says that tomatoes are by far the best sources of lycopene. But certain things affect how much is absorbed in the body.
"Contrary to the popular belief that fresh is always better, when it comes to lycopene, fresh is not better," says Johnson. One factor that helps absorption is how much the tomato is processed -- meaning if it is diced and cooked.
Johnson explains, "Lycopene in food is bound up in the cell walls of the plant. Chopping and heating help break up that plant structure, so lycopene is released and better absorbed."
Fat also affects lycopene. "Lycopene is fat-soluble, meaning it needs some fat to be absorbed in the gut," says Johnson. So tomato sauce or well-cooked, diced tomatoes with a little oil yield more lycopene than fresh, plain tomatoes.
Why Not Just Pizza?
A few years ago, research found that pizza, with its lycopene-rich tomato sauce, was linked to a reduced risk for prostate cancer. But if you think this gives you license to eat super-supreme pizzas, think again.
Pizza was also associated with unhealthy lifestyle practices.
Zhou says, "In general, pizza is not considered a healthful food because it's high in saturated fat and usually lacking in vegetables. The tomato sauce or tomatoes on the pizza was more likely the benefit here -- not the pizza itself."
So, What Should You Eat?
"But people shouldn't expect to add some tomato products to an unhealthful diet and think the problem is solved. Instead, the focus should be to eat a healthful diet abundant in various fruits and vegetables that includes tomatoes and tomato products."
Johnson adds, "To advocate one food or group of foods is all right, but you don't want to go overboard. As humans, we're not just concerned with cancer. We're also concerned with heart disease, diabetes, obesity, etc. The focus should be on a whole diet that helps prevent many diseases.
"Fortunately, it's pretty much the same message for all these diseases -- eat a diet rich in fruits and vegetables and low in fat that includes a variety of foods," she says.
Zhou agrees. "Lycopene is just one factor of many. It likely interacts with other plant chemicals in the tomato and other fruits and vegetables to help fight disease. So the whole dietary pattern is important."
What About Supplements?
Lycopene supplements pack high doses of the carotenoid into pills. Sometimes these amounts are far more than can be eaten in a typical diet.
Johnson believes that lycopene supplements are counterproductive. "All of the carotenoids, including lycopene, have very similar structures that may rival each other to be absorbed. So if you overdo it with one carotenoid, you could lose the benefit of another. Different carotenoids may lower the risk for different cancers, so you may miss out on those advantages."
Johnson adds, "Lycopene supplements are expensive. And there's no guarantee they are absorbed well. Compare a bottle of tomato juice with a bottle of lycopene supplements -- the juice is a lot cheaper, you're taking in a realistic amount of lycopene, and you get the benefit of other nutrients in the juice."