In preliminary studies, purple grape juice given to female rats led to reductions in both the number and size of the cancerous cells.
The study, led by Keith Singletary, a professor of nutrition at the University of Illinois at Urbana-Champaign, is being presented tomorrow at the International Scientific Conference on Complementary, Alternative and Integrative Medical Research, which is co-sponsored by Harvard Medical School, UCSF Medical School and the Beth Israel Deaconess Medical Center.Scientists are not sure exactly which part of the grape leads to the reductions or how the mechanism works, but they suspect it has to do with the pigments.
"This is something that's not popping out of the blue as totally a new phenomenon," says Singletary, who is also the director of the University of Illinois's Functional Foods for Health. "There has been some evidence from the scientific literature that there is biological activity in polyphenols, at least as an antioxidant -- and antioxidants are believed to be one important contributor to preventing certain diseases."
Polyphenols are compounds found in plant-based foods. Pigments are included within this category, and this is where Singletary is planning to focus future research.
"We think what is unique and interesting to follow is whether purple pigments may be part of or most of the protective effect," he says. "The results are preliminary, but they do warrant further investigation."
Previous studies have shown that the antioxidants in purple grape juice are heart-healthy.
In this series of experiments, Singletary and his team administered a tumor-inducing compound to female rats then, one week later, began feeding the animals three different concentrations of Concord grape juice. The researchers used commercial varieties such as Welch's and Billerica in concentrated form, then diluted it in drinking water. A control group of rats received the carcinogen and were then fed fluids with calories, carbohydrates and organic acids similar to those found in the grape juice, but without the polyphenols.
The rats that had received the two higher concentrations of grape juice developed tumors, but tumor mass was reduced by between 28 percent and 36 percent compared with rats in the control group.
The number of tumors per animal was also reduced by 45 percent to 65 percent in the same two high-concentration groups.
"We found that the grape-consuming rats, especially those having the higher amount, had fewer tumors and the tumors appeared to be smaller," Singletary says.
In a related experiment, the researchers found Concord grape color extract inhibited the proliferation of cancer cells when added to breast cancer cells from rats in test tubes.
Still, none of these results are a call to start eating only grapes.
"It's an interesting topic, but you have to keep in mind that it's a single study and it's conducted in animals. It's difficult to draw any sort of definitive conclusions or dietary recommendations to a human population based on this," says Rachel Zinaman, a clinical research dietician at the Evelyn H. Lauder Breast Cancer Center at Memorial Sloan-Kettering Cancer Center in New York City.
Next, Singletary says, he's going to try to pinpoint exactly which constituents in purple grape juice are responsible for the effects.
"We're basically trying to understand the mechanisms of what is occurring," Singletary says. "We think it's worth looking at for possible benefits."
What To Do
To help prevent breast and other forms of cancer, make sure you eat a balanced diet.
"We always fall back on same bottom line: It's variety," Zinaman says. "Consume a well balanced diet which is low in fat and high in fiber. You want to use all the fruits and vegetables. If a study wants you to include grapes, that's OK. Just don't fall back on just one food."