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UC Davis Health System

UC Davis Health System

Diet high in fruit, vegetables and fiber and low in fat does not appear to reduce risk of breast cancer recurrence more than the "5-a-day" diet

Photo of vegetables The WHEL Study found that a diet high in fruits and vegetables and low in fat did not lower the risk of breast cancer recurrence more than the '5-a-day' diet.

Women with early stage breast cancer who adopted a diet very high in vegetables, fruit and fiber and low in fat did not have a lower risk of breast cancer recurrence compared to women who followed a diet of five or more servings a day of fruit and vegetables (the “5-A-Day” diet), according to a study in the July 18 issue of the Journal of the American Medical Association (JAMA).

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.

Nation-wide research

Led by John P. Pierce, of the University of California, San Diego, researchers around the country, including those at UC Davis Health System, 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). In the Sacramento region, the UC Davis portion of the study included 500 women. Women were enrolled between 1995 and 2000 and followed up through June 2006.

“We followed women for an average of 7.3 years and found no evidence that the adoption of a diet very high in vegetables, fruit and fiber and low in fat was more effective in preventing breast cancer recurrence or death than the nationally recommended '5-A-Day' fruit and vegetable diet among women with previously treated, early stage breast cancer.”
— Ellen Gold, UC Davis professor

“We followed women for an average of 7.3 years and found no evidence that the adoption of a diet very high in vegetables, fruit and fiber and low in fat was more effective in preventing breast cancer recurrence or death than the nationally recommended '5-A-Day' fruit and vegetable diet among women with previously treated, early stage breast cancer,” said Ellen Gold, professor and interim chair of the UC Davis Department of Public Health Sciences.

Gold indicated that the WHEL investigators have confidence in the study's results because of its large sample size and a rigorous design that included careful follow up, retention and documentation to make sure that the project's dietary interventions were implemented and well-maintained by study participants. It also included a high quality statistical analysis of the data.

The study groups

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. A total of 315 deaths were 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.

“The WHEL study was designed to enable breast cancer survivors to make well-informed decisions about potential preventive measures, such as diet," said Gold. "We reported last month that women who maintained a diet that follows national dietary guidelines and who got regular exercise enjoyed better disease-free survival. Today's data persuasively show that adding an intensive dietary pattern does not confer further benefits.”

Gold noted it is well-known that a diet high in vegetables, fruit and fiber and low in fat still offers significant health benefits for women in terms of such things as reducing diabetes and high blood pressure and maintaining a healthy weight.

In the next few months, WHEL study researchers plan to conduct additional analyses to determine if the dietary intervention is more helpful in certain subgroups, since breast cancer is a heterogeneous disease and thus requires multiple preventive approaches, depending on the disease profile of the individual woman with breast cancer.

The study, "Influence of a Diet Very High in Vegetables, Fruit, and Fiber and Low in Fat on Prognosis Following Treatment for Breast Cancer," JAMA 2007; 298(3):289-298, is available at http://jama.ama-assn.org/.