TUESDAY, July 17, 2007 (HealthDay News) -- While a healthy diet remains a mainstay of cancer prevention, eating more than the recommended amounts of fruits, vegetables and fiber won't give you added protection against breast cancer, new research suggests.
This study of breast cancer survivors found no statistically significant benefit in terms of being diagnosed with breast cancer again for women who followed a diet that encouraged eating at least eight servings of vegetables and fruits, at least 30 grams of fiber, and no more than 15 percent to 20 percent of fat.
"Clearly, there's a threshold for prevention. You don't have to go overboard. The national guidelines are good enough," said study author John Pierce, director of cancer prevention at the Moores Cancer Center at the University of California, San Diego.
Results of the study are in the July 18 issue of the Journal of the American Medical Association.
Breast cancer accounts for about one in three of all cancers diagnosed in women, according to the American Cancer Society (ACS). More than 200,000 women are diagnosed with breast cancer in the United States each year, and more than 40,000 American women die from breast cancer annually, according to the ACS.
Many previous studies have suggested that a diet full of fruits, vegetables and fiber, but low in fat, can reduce the risk of certain cancers. To assess whether or not improving the diet over and above what's already recommended could provide a more significant benefit, Pierce and his colleagues recruited more than 3,000 women who'd already been diagnosed with and treated for early-stage breast cancer.
The women were between the ages of 18 and 70 and had no evidence of recurrent breast cancer at the start of the study.
The volunteers were randomly assigned to one of two groups. The intervention group included 1,537 women who were given telephone counseling along with cooking classes and newsletters that recommended five servings of vegetables, one serving of vegetable juice, three servings of fruit, at least 30 grams of fiber and no more than 15 percent to 20 percent of daily calories from fat. A comparison group included 1,551 women who were given printed materials that recommended the current national guidelines of five servings of fruits and vegetables a day.
"These were healthy breast cancer survivors who were already eating at least five servings of fruits and vegetables. We wanted to know what happened when you really ramped that up. Some women ate 12 or more servings of fruits and vegetables a day," Pierce said.
Throughout the study, the women were periodically asked to recall their diet in the past 24 hours. The researchers also checked for changes in certain substances in the blood that indicate fruit and vegetable intake. The average follow-up time was 7.3 years.
After four years, the researchers found that vegetable intake had increased in the intervention group by 65 percent, while fruit consumption was up by 25 percent. Fiber intake was also increased, by as much as 30 percent, and fat intake was down 13 percent.
Yet, during the study period, there were no statistically significant differences in the rates of breast cancer recurrence. During the study period, 16.7 percent of women in the intervention group vs. 16.9 percent of women in the comparison group received a diagnosis of invasive breast cancer.
There were also no statistically significant differences in mortality. In the intervention group, 10.1 percent of the women died compared to 10.3 percent in the comparison group.
Does that mean eating well won't help prevent cancer from returning?
"For women with breast cancer, the answer is out on whether or not there's a single constituent in the diet that will help. But, for overall health, maintaining a healthy weight and eating a healthy diet is always good," said the co-author of an accompanying editorial, Susan Gapstur, associate director of cancer prevention and control for the Robert H. Lurie Comprehensive Cancer Center at Northwestern University in Chicago.
Gapstur pointed out that the women in the study weren't able to meet the suggested reduction in fat intake. Additionally, she said that there appeared to be some discrepancy in the number of calories consumed. By the end of the study, the average number of reported calories consumed in the intervention group was 180 less per day. Gapstur said that such a change would have resulted in weight loss instead of the slight increase that the women experienced.
Rather than just one aspect of diet or lifestyle, Gapstur said she believes the next question researchers have to answer is all of these factors as a whole. "We have to address the full spectrum -- diet, physical activity and obesity," she said.
In the meantime, she said, "At the end of the day, it's never wrong or bad to eat healthfully."
Pierce added that exercise patterns are also important and suggested that women exercise moderately for about 30 minutes a day.
More information
To learn more about breast cancer prevention, visit the National Cancer Institute.
