Not Too WHEL: Diet and Breast Cancer Recurrence

Abstract & commentary

By Russell H. Greenfield, MD. Dr. Greenfield is Clinical Assistant Professor, School of Medicine, University of North Carolina in Chapel Hill, and Visiting Assistant Professor, University of Arizona, College of Medicine in Tucson; he reports no financial relationships relevant to this field of study.

Source: Pierce JP, 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;298:289-298.

In a large, multi-institutional (7 sites), randomized, controlled study of dietary change, researchers sought to determine whether a significant increase in vegetable, fruit, and fiber intake, together with a decrease in total dietary fat intake, reduces risk of recurrent and new primary breast cancer and all-cause mortality among women with previously treated early stage breast cancer (aged 18-70 years). The intervention group (n = 1537) was assigned to a telephone counseling program supplemented with 12 cooking classes during the first year, and then monthly newsletters during the second year that promoted daily targets of 5 vegetable servings plus 16 oz of vegetable juice; 3 fruit servings; 30 g of fiber; and 15-20% of energy intake from fat. The comparison group (n = 1551) was provided with print materials describing "5-A-Day" dietary guidelines that also emphasized > 20 g fiber per day and < 30% total energy intake from fat. Dietary intake was assessed with 4 prescheduled 24-hour dietary recalls conducted by telephone on random days over a 3-week period, stratified for weekend vs weekdays, that occurred at baseline, 1 year, 4 years, and 6 years, and on 50% random samples at 6, 24, and 36 months. Clinic visits occurred at baseline, 1, 2, or 3 years (randomly determined), and 4 and 6 years. Prior to clinic visits, subjects were mailed questionnaires that included measures of physical activity and psychosocial functioning. The principle outcomes of interest were invasive breast cancer events (recurrence or new primary) or death from any cause. Two independent oncologists reviewed the medical records of subjects diagnosed with recurrent or new primary breast cancer. Throughout the study, women in both groups received similar medical care.

Data analysis and laboratory studies confirmed that subjects in the intervention groups had maintained a significantly increased intake of fruits, vegetables, and fiber as compared with the comparison group, where intakes changed but modestly, except for a 13% increase in total fat intake. Over a mean follow-up period of 7.3 years, a total of 256 women in the intervention group (16.7%) and 262 subjects in the comparison group (16.9%) experienced an invasive breast cancer event; 155 women in the intervention group (10.1%) died, as compared with 160 in the comparison group (10.3%). Over 80% of all deaths were related to breast cancer. Disease-free survival curves were virtually identical across groups. No between-group differences were found for depression, social support, or quality of life during the most intensive period of intervention (year 1). Pierce and colleagues concluded that among survivors of early stage breast cancer, adoption of a diet that is very high in vegetables, fruit, and fiber and low in fat does not reduce additional breast cancer events or mortality.

Commentary

For years, many of us have relied upon a wealth of preclinical data and the smattering of clinical research strongly suggesting that high intakes of fruit, vegetables, and fiber, and a lessened reliance upon high fat foods, constitute an effective preventive strategy against development of breast cancer. Our belief was so strong that this position assumed the station of fact in many circles. Unfortunately, results of this extremely well done trial serve as a sobering reminder that things are rarely as linear or as simple as we would like.

The methodology employed was strong, with a formidable sample size (n = 3,088), as well as significant length and completeness of follow-up. While participants did not attend the majority of classes and may not have read all the newsletters, the approach parallels what might be seen in real life, and the results thus seem generalizable. It is notable that only 14% of subjects could be classified as minorities. Even more notable, the fact that at baseline women in both groups were consuming an average of more than 7 servings of fruits and vegetables a day (likely in response to the diagnosis of breast cancer). Lastly, it is important to remember that the trial did not address carcinoma in situ or stage I tumors < 1 cm in size.

It appears that the dietary manipulation described herein does not have the desired breast cancer chemopreventive effect hoped for in women previously treated for breast cancer. However, the trial did not address the effect of dietary intervention on primary prevention of breast cancer. It is possible that similar dietary interventions might mitigate circumstances associated with other forms of cancer. In addition, diets high in fruits, vegetables, fiber, and omega-3 fatty acids are heart healthy.

Is it time to ditch the farmer's market and hit the burger joint? No. The results of this trial are disappointing, but the evidence of health benefits associated with a diet high in fruits, vegetables, and fiber and low in total fat remain compelling. We can and should continue to recommend such a diet to our patients, even those with a history of breast cancer, though we cannot point to a direct breast cancer-related benefit for women in this group.