Eating at least five servings of fruits and vegetables may reduce risk of death in women with breast cancer, but eating more than the recommended number of servings may not further reduce the risk of cancer recurrence and mortality, according to a study published in the July 18 issue of the Journal of the American Medical Association.

“Considerable evidence from preclinical studies indicates that plant-derived foods contain anticarcinogens. A comprehensive review of the literature found that a diet high in vegetables and fruit probably decreases breast cancer risk and that a diet high in total fat possibly increases risk,” the searchers write in their report.  “However, evidence of an association between a diet high in vegetables and fruit and low in total fat and prevention of cancer progression has been mixed in epidemiological studies.”

The U.S. government recommends that adults eat 5 servings of fruits and vegetables a day to prevent diseases.   In the current study, researchers found that eating more than 5 servings of fruits and vegetables per day did not help women reduce their risks of breast cancer recurrence and dying from the disease compared to those who just ate five servings.

The 7-year study involved 3,100 women who were diagnosed with early stage breast cancer at age 18 and 70 and had underwent surgery before entering the study, which was conducted by researchers from multiple medical centers where study subjects were enlisted and followed.

In the so-called Women's Health Eating and Living trial (WHEL), participants were randomly assigned one of two dietary regimens. One group of women was asked to eat more than 5 servings of fruit and vegetables per day, to reduce fat intake to 15 to 20 percent of the total calories and to have 30 grams of fiber a day.

The other group that served as controls were told to eat 5 servings of fruits and vegetables a day, 20 grams of fiber and getting less than 30 percent of their calories from fat.

John P. Pierce, Ph.D., of the University of California, San Diego, La Jolla, Calif., and colleagues who conducted the study found that the rates of deaths and breast cancer recurrence were nearly identical for both groups, meaning the dietary difference observed in the study did not make any significant difference in the prognosis of breast cancer in terms of cancer recurrence and mortality.   But where high intake of fruits and vegetables delayed the recurrence and death from the cancer was not reported.

For the study, women’s adherence to the dietary regimens was monitored by phone and written questionnaires.   Blood samples were also taken annually during the first four years of the study and again at the six-year mark.

At the end of the first four years of the study, the women in the study group were eating 65 percent more vegetables, 25 percent more fruit, 30 percent more fiber and 13 percent less fat than the women in the control group. Blood tests showed that a biomarker linked to intake of vegetables and fruits were 43 percent higher in the intervention group.   But the marker was monitored only once a year, which could introduce errors.

It was found that 16.7 percent of the women on the high vegetable diet experienced recurrence of breast cancer compared to 16.9 percent in the control group who ate less fruit and vegetables.   10.1 percent of women in the intervention group died, mostly from breast cancer, compared to 10.3 percent in the control group.

"I was really surprised and, frankly, a little disappointed by the results," said Marcia Stefanick, PhD, professor of medicine at the Stanford Prevention Research Center and the senior author of a study. "We expected the two-fold increase in vegetables and fruits, plus the increased fiber and reduced fat to make a difference in the recurrence rates."

"I would certainly hope that people don't interpret these results as evidence that eating a lot of vegetables doesn't make a difference in breast cancer," she said. "What it shows is that getting more than the recommended amounts doesn't change the recurrence rate for women who have already completed treatment for early-stage breast cancer."

However, the mortality rate in women who ate more than five servings of fruit and vegetables was reduced by nearly 50 percent, the Physicians Committee for Responsible Medicine (PCRM) said in its news release, reminding audience of the benefit from high consumption of fruits and vegetables.

According to the PCRM, the 50 percent reduction in mortality in women with breast cancer due to high intake of fruits and vegetables was also reported in another study by Piece’s group published in the Journal of Clinical Oncology 2007;25:2345-51.

In addition, previous studies have shown that low-fat, high-fiber diets improve cancer survival. The Women’s Healthy Eating and Living study showed that reducing dietary fat and boosting fiber cut the risk of breast cancer recurrence by 24 percent. The results were published by Chlebowski RT and colleagues in Journal of National Cancer Institutes, 2006; 98:1767-76

The researchers said the study did not exclude the benefits of consuming more than 5 servings of fruits and vegetables a day in some subgroups.    Previous reports from the WHEL study, cited by the PCRM, have shown that diet changes affect the hormones that influence cancer growth and in a substudy of 291 participants, increased intake of fiber and reduced intake of dietary fat were associated with reduced serum concentrations of estradiol, bioavailable estradiol, estrone, and estrone sulfate, meaning it would reduce risk of breast cancer.   The results were published by Rock CL and colleagues in the Journal Clinical Oncology 2004;12: 2379-2387.

One drawback of the JAMA study is that adherence to the dietary regimens was questionable, intake of calories were not restricted and many other dietary factors were not considered such as animal protein.   Both the study group and control group experienced weight gain, indicating that they might increase intake of animal protein.   Early studies by Colin T Campbell, Ph.D., nutrition professor from Cornell University showed high intake of animal protein and fat were linked with increased risk of breast cancer.

It is not clear whether the breast cancer patients were receiving any chemotherapy or taking any anti-cancer medications.   Any drug would potentially complicate the effect of fruits and vegetables on the risk of breast cancer recurrence, a scientist affiliated with foodconsumer.org suggested.  

For more information, read the following:

 1. Pierce JP, Stefanick ML, Flatt SW, et al. Greater survival after breast cancer in physically active women with high vegetable-fruit intake regardless of obesity. J Clin Oncol 2007;25:2345-51.

2. Pierce JP, Natarajan L, Caan BJ, et al. Influence of a diet very high in vegetables, fruit, and fiber and low in fat on prognosis following treatment for breast cancer: The Women’s Healthy Eating and Living (WHEL) randomized trial. JAMA 2007;298:289-98.

3. Rock CL, Flatt SW, Thomson CA, et al. Effects of a high-fiber, low-fat diet intervention on serum concentrations of reproductive steroid hormones in women with a history of breast cancer. J Clin Oncol 2004;12:2379-2387.

4. Chlebowski RT, Blackburn GL, Thomson CA, et al. Dietary fat reduction and breast cancer outcome: interim efficacy results from the Women's Intervention Nutrition Study. J Natl Cancer Inst 2006;98:1767-76.