WEDNESDAY, Nov. 5, 2003 (HealthDayNews) -- Men who want to reduce their risk of prostate cancer should opt for tomato products, not simply the lycopene found in them, a new animal study suggests.
Rats fed diets that contained whole tomato powder, including lycopene and other compounds, had a 26 percent lower risk of prostate cancer death than those that were fed diets containing pure lycopene or standard diets without either lycopene or tomato products, researchers report in the Nov. 5 issue of the Journal of the National Cancer Institute.
"Since lycopene is the carotenoid in tomatoes that gives it its red color and has antioxidant properties, many assume the reasons tomatoes may protect, if they do, from cancer is because of the lycopene," says study author Dr. Steven K. Clinton, a medical oncologist at Ohio State University.
"The lab animal study supports the epidemiological association that tomato products are associated with a lower risk [of prostate cancer] but does not support the hypothesis that it is lycopene alone mediating that effect," Clinton adds.
His study also showed that cutting calories may be wise.
The rats in the project were divided not just into the lycopene and tomato powder groups, but into groups that got unlimited access to food and those in which calories were reduced by 20 percent.
Those rats that were cut back 20 percent on calories had a 32 percent lower risk of prostate cancer death compared to those with unlimited access to food, the researchers say.
This year, 220,900 new cases of prostate cancer are expected to be found, according to the American Cancer Society, and 28,900 men are expected to die from it.
While many Americans would prefer to take a lycopene pill, Clinton says, his study points to the benefit of getting tomato products from the diet in the form of the vegetable itself, or juice, soup or sauces such as tomato or salsa.
The caloric restriction, another part of the study, was modest, he says, compared to other studies that looked at reductions of 30 percent or 40 percent.
"This reinforces the importance of preventing obesity," Clinton says. Earlier this year, a study published in the New England Journal of Medicine reported that being overweight or obese seems to be responsible for 14 percent of cancer deaths in men and 20 percent in women, with prostate cancer one of the types associated with being overweight.
"The energy restriction and the tomato products seem to have additive benefits" in reducing prostate cancer risk, Clinton says.
So how much tomato is protective? "I don't think we can extrapolate directly, but in the rat diet, it was 10 percent of the entire diet," Clinton says. However, he believes it would be reasonable to advise men who want to reduce their risk to eat about one tomato serving a day, or five to seven servings a week.
"Tomato juice, soup, sauce, they all fit in," he says. "At this point, we have no reason to believe someone must have only fresh tomatoes."
In an editorial accompanying the study, Dr. Peter H. Gann notes Americans may be on their way to fulfilling the "eat more tomatoes" recommendation -- they average 91 pounds of tomatoes per capita per year.
"What's interesting about this study is we have direct comparisons of pure lycopene versus tomatoes," says Gann, an associate professor of preventive medicine at the Robert H. Lurie Comprehensive Cancer Center at Northwestern University.
The study also lends weight to the value of caloric restriction as an anticancer measure, he adds. Why reductions work isn't certain, he says. But the speculation is that caloric restriction leads to hormonal changes that reduce the body's ability to stimulate tumor growth.