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. 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 authors write.
John P. Pierce, Ph.D., of the University of California, San Diego, La Jolla, Calif., and colleagues conducted the Women's Healthy Eating and Living (WHEL) Study to assess whether a dietary pattern very high in vegetables, fruit, and fiber and low in fat reduces the risks of recurrent and new primary breast cancer and all-cause death among women with previously treated early stage breast cancer. The randomized controlled trial included 3,088 women who were previously treated for early stage breast cancer (18 to 70 years old at diagnosis). Women were enrolled between 1995 and 2000 and followed up through June 2006.
The intervention group (n = 1,537) was randomly assigned to receive a telephone counseling program supplemented with cooking classes and newsletters that promoted daily targets of five vegetable servings plus 16 oz. of vegetable juice; three fruit servings; 30 grams of fiber; and 15 percent to 20 percent of energy intake from fat. The comparison group (n = 1,551) was provided with print materials describing the 5-A-Day dietary guidelines.
From comparable dietary patterns at baseline, the intervention group achieved and maintained the following statistically significant differences vs. the comparison group through four years: servings of vegetables, +65 percent; fruit, +25 percent; fiber, +30 percent, and energy intake from fat, -13 percent. Throughout the study, women in both groups received similar clinical care. During the study, 518 participants had a breast cancer event, including 256 participants (16.7 percent) in the intervention group and 262 participants (16.9 percent) in the comparison group. There were 315 deaths reported within the study period, with 155 (10.1 percent) in the intervention group and 160 (10.3 percent) in the comparison group. More than 80 percent of all deaths were due to breast cancer. No significant benefit in preventing breast cancer recurrence was observed overall among population subgroups characterized by demographic characteristics, baseline diet, or type of initial tumor or breast cancer treatment.
In conclusion, during [an average] 7.3-year follow-up, we found no evidence that adoption of a dietary pattern very high in vegetables, fruit, and fiber and low in fat vs. a 5-a-day fruit and vegetable diet prevents breast cancer recurrence or death among women with previously treated early stage breast cancer, the authors write.
Editor's Note: Please see the article for additional information, including other authors, author contributions and affiliations, financial disclosures, funding and support, etc.
In an accompanying editorial, Susan M. Gapstur, Ph.D., and Seema Khan, M.D., of the Feinberg School of Medicine, Northwestern University, Chicago, write that there are a number of questions that need to be examined regarding diet and cancer risk.
Several issues remain to be addressed regarding the effects of dietary interventions on breast cancer prognosis. It is becoming increasingly clear that evaluating dietary effects is complex and requires careful monitoring to ensure adherence to the intervention goals so that any hypothesized effect can be detected. In addition, studies assessing whether breast cancer prognosis would be improved with interventions that focus on the complex components of energy balance (i.e., physical activity and energy intake) appear warranted. Unfortunately, available data do not support best practice dietary recommendations to improve long-term prognosis for early stage breast cancer survivors.
ama-assn/