Intensive Diets Do Not Reduce Breast Cancer Recurrence Risk More Than Standard "5-A-Day" Interventions

July 19, 2007 — Breast cancer survivors who follow a diet that is very high in vegetables, fruit, and fiber and low in fat do not have a lower risk for disease recurrence or mortality compared with women who followed a diet of 5 or more servings a day of fruit and vegetables.
"The conclusion is that women do not need to eat more than the recommended 5 a day of vegetables and fruits or reduce their fat intake below 30% of energy," said lead author John P. Pierce, PhD, Sam M. Walton Professor for Cancer Research at the Moores University of California, San Diego, Cancer Center in La Jolla. The study appeared in the July 18 issue of the Journal of the American Medical Association.
Strong evidence from preclinical studies has shown that plant-derived foods contain anticarcinogens, and published literature suggest that diets rich in fruits and vegetables may reduce the risk for breast cancer. There is also some evidence that a diet high in total fat may elevate the risk. However, epidemiologic studies have produced mixed results in establishing an association between a diet high in fruits and vegetables and low in total fat and preventing disease progression in breast cancer patients, write the authors.
The current study, known as Women's Healthy Eating and Living (WHEL), was conducted to examine if increasing dietary intake of fruits, vegetables, and fiber, while lowering dietary fat, would reduce the risk for recurrence, new primary invasive breast cancer, or mortality among survivors of early-stage breast cancer.
"The WHEL Study involved a healthy group of breast cancer survivors who had a low rate of events," Dr. Pierce told Medscape. "It demonstrated that there is no need to go to extremes in order to improve prognosis. The 5-a-day is a moderate dietary pattern, and with 30 minutes of physical activity a day, appears to be enough to improve prognosis."
In an accompanying editorial, Susan M. Gapstur, PhD, and Seema Khan, MD, from Northwestern University in Chicago, Illinois, point out that the results of the WHEL Study conflict with those of another large randomized trial, the Women's Intervention Nutrition Study (WINS). The WINS assessed the effect of a low-fat diet (15% of total calories) on breast cancer recurrence or survival. Interim results showed a significant benefit on the hazard ratio (HR) for relapse-free survival after a median of 5 years among women randomized to the low-fat dietary intervention group as compared with the control group, explain the editorialists. An exploratory analysis suggested that the beneficial effect of a low intake of fat might be restricted to patients with breast cancers that were estrogen-receptor and progesterone-receptor negative.
"These conflicting results from the WHEL Study and WINS regarding the potential benefits of a dietary modification on long-term breast cancer prognosis require careful consideration," they write. "In particular, a key issue is the difference in energy balance that was achieved between WINS and WHEL Study participants."
In WINS, the women randomized to receive the low-fat intervention experienced significant weight loss, and there was a 6-lb (2.7-kg) weight difference between intervention and control women at the end of 5 years. However, in the WHEL Study, the decrease in the self-reported total energy intake was similar for both the intervention and control groups, and a small weight gain was experienced by patients in both groups.
"It is unclear whether the difference in energy balance, as reflected by weight change, partly accounts for the beneficial effects of the intervention on survival observed in WINS and no intervention effect as observed in the WHEL Study," write Drs. Gapstur and Khan. "Taken together, these data support findings from observational studies suggesting that a high level of obesity, weight gain, or both after diagnosis is adversely associated with breast cancer disease-free survival and overall survival."
In the WHEL Study, 1537 women previously treated for early-stage breast cancer were randomly assigned to increasing their consumption of fruits to 3 servings/day, vegetables to 5 servings/day, and fiber to 30 g/day, while lowering fat intake to 15% to 20% of total calories. The control group (n = 1551) was given printed educational materials that outlined the "5-a-Day" dietary guidelines. The patients were followed up for an average of 7.3 years.
Results showed that the intervention group achieved and maintained several statistically significant differences, compared with the control group, during a 4-year period; servings of vegetables, +65%; fruit, +25%; fiber, +30%, and energy intake from fat, -13%. Women in both groups received comparable clinical care.
Although the actual fat intake of the patients in the intervention group was higher than the planned 15% to 20%, Dr. Pierce explained that the WHEL Study achieved the largest validated dietary change of any trial. "We used challenging behavioral targets such as 15-20% from fat as part of our motivational strategy to achieve large differences between groups."
"For this study," he said, "the important difference is the between-group differences. Large and highly significant between-group differences were observed at all study points, even when we conservatively assumed that those who did not provide dietary data were eating the same as the comparison group."
During the 7.3-year study period, a total of 518 women had a breast cancer event. This included 256 (16.7%) women from the intervention group vs 262 (16.9%) control subjects. Of the 315 deaths that occurred, 155 (10.1%) were in the intervention group vs 160 (10.3%) in the control group.
Dr. Pierce pointed out that WHEL focused on vegetables, fruit, fiber, and fat. "If we had also had concentrated on sugar and junk food, we would have seen a weight reduction. We did not want a weight reduction for this study, as we wanted to address any unique role of the dietary components that we targeted."
Responding to comments made by the editorialists, Dr. Pierce added, "We agree... that there is a need for a study that focuses on adding physical activity and weight reduction to a 5-a-day dietary pattern."
The WHEL Study was initiated with support from the Walton Family Foundation and continued with funding from a National Cancer Institute grant.
JAMA. 2007;298:289-298, 335-336.