In a study done at Ohio State University in Columbus, the berries were found to have a potent effect against colon cancer in animals.
"We found that if we added black raspberries to the diet of rats after we had treated them with a carcinogen, the berries prevented precancerous changes from going on into malignancies," says Gary Stoner, professor and chair of environmental health sciences at the School of Public Health at Ohio State. "We had about an 80 percent reduction in the number of malignant tumors in the colon and also a reduction in tumor size."The results were published in a recent issue of Nutrition and Cancer.
In this study, researchers injected laboratory rats with azoxymethane, a carcinogen known to cause colon tumors. The rats were then divided into four groups; three were fed different amounts of freeze-dried berries and one, acting as a control, got no berries at all. The black raspberries were fresh-picked locally, then freeze-dried within an hour of picking so most of the nutrients stayed intact.
At the end of the trial, the black raspberries had demonstrated a clear effect: The more berries a rat ate, the fewer malignant tumors it had.
Rats who received diets of 2.5 percent and 5 percent black raspberries experienced a 28 and 35 percent reduction in the number of tumors, respectively. The lucky rats who had a diet of 10 percent berries had a reduction of about 80 percent.
The berries reduced not only the prevalence of malignant tumors, but their size as well. The researchers also found the diet cut the amount of oxidation damage to the animals' tissues. Black raspberries exhibited 40 percent more antioxidant activity than strawberries and 11 percent more than blueberries.
Berries contain vitamins C, A, and E, the minerals calcium and selenium, and zinc compounds such as anthocyanins and phenols, all of which seem to act against certain types of cancer. Previous studies showed a similarly beneficial effect against cancer of the esophagus, but no effect against lung cancer.
Human trials, which in part are trying to isolate the specific compounds in the berries that have the beneficial effect, started this week. Experts warn, though, that such efforts are not often successful.
"Isolating will probably prove very difficult. Unless you're dealing with a very, very specific carcinogen that only produces cancer in one narrow mechanism, it's unlikely that you're going to find a single dietary substance that will protect against multiple cancers and that you could turn into a drug," says Dr. William Audeh, a medical oncologist in the division of hematology and oncology at Cedars-Sinai Cancer Center in Los Angeles.
The human equivalent of what the rats ate would be about two bowls of berries a day -- but bear in mind the rats also received a large amount of carcinogen.
"It would be very nice to say that we are going to reduce raspberries to a dry capsule and take it once a day and prevent all sorts of cancers, but I don't think the science is heading that way," Audeh says. "You really need to eat what nature created in the first place."
Until studies say something different, stick to the National Cancer Institute's recommendation: five servings of fruits and vegetables every day. No one says you can't add berries to that mix.