Study: Loading Up on Fruits and Veggies Won't Lower Breast Cancer Recurrence

Thu Jul 19, 8:00 PM ET
A long-term study of breast cancer survivors shows that eating more than the recommended 5 daily servings of vegetables and fruit has no effect on breast cancer recurrence or deaths. Although researchers are disappointed by the finding, they say women should still strive to fit plenty of these healthy foods into their diet because they have other benefits.
"There are many reasons women should eat a healthy diet, but for breast cancer, there's little evidence that the foods you eat impact risk," says Colleen Doyle, MS, RD, director of nutrition and physical activity at ACS. "What is important is how much you eat, because being overweight is an established risk factor for developing postmenopausal breast cancer, and it also increases the risk of recurrence. That's the message we want breast cancer survivors to know: Watching your weight is really important."
The study, called the Women's Healthy Eating and Living (WHEL) Trial, was led by a team from the University of California, San Diego, and included researchers from 7 other institutions. The participants were more than 3,000 women (pre- and post-menopause) who had been treated for stage I, II, or III breast cancer.
The women were randomly assigned to 2 diet groups: The control group was told to follow US dietary guidelines, which recommend eating at least 5 servings of fruits and vegetables each day, more than 20 grams of fiber, and no more than 30% of calories from fat.
The second group was told to boost their fruit and veggie intake to include 5 vegetables, 3 fruits, 16 ounces of vegetable juice, and 30 grams of fiber each day. They were also supposed to cut their fat intake to 15%-20% of total calories. The women in this group got periodic telephone counseling, cooking classes, and newsletters aimed at helping them stick with this eating plan.
Researchers tracked the women's progress for more than 7 years on average. They saw clear differences in the amount of fruits and vegetables the women in the 2 groups ate, although after year 4 of the study, the gap between the 2 groups tended to narrow. On average, the women in the second group never achieved their goal of getting only 15%-20% of their calories from fat; in fact, by year 6, they were eating a higher percentage of fat than at the beginning of the study.
Despite the difference in fruit and vegetable consumption, the 2 groups had very similar cancer experiences during the 7 years. About 17% of women in each group had a recurrence during the study period, and about 10% of women in each group died.
"I was really surprised and, frankly, a little disappointed by the results," says the study's senior author Marcia Stefanick, PhD, professor of medicine at the Stanford Prevention and Research Center at Stanford University School of Medicine. Stefanick and colleagues had hoped that doubling the amount of fruits and vegetables, along with increased fiber and reduced fat, would make a difference when it came to recurrence.
But it may be that diet is important in the context of weight control. For instance, Doyle says, the recent Women's Intervention Nutrition Study (WINS) also looked at dietary factors -- fat intake, in particular -- although in a slightly different group of breast cancer survivors. Early results showed that a low-fat diet seemed to result in benefits, especially for women with estrogen receptor-negative tumors. However, most of the women on the low-fat diet also experienced significant weight loss. While the studies aren’t directly comparable, the difference in weight loss may contribute to the different findings in the WINS and the WHEL studies, as women in the WHEL study actually experienced a small increase in weight.
Eating Your Vegetables (and Fruits) Still a Great Idea
So if loading up on fruits and vegetables does not affect breast cancer recurrence, is there any reason for a survivor to go out of her way to incorporate them into her diet?
"Absolutely!" Doyle stresses. "Fruits and vegetables are packed with nutrients and low in calories -- and more evidence suggests they can help with weight control. That's great news for all of us!"
Plus, other studies have shown that eating more than 5-a-day can reduce the risk of heart disease and stroke, and can help keep blood pressure under control, says WHEL study co-author Cheryl Rock, PhD, RD, of the Moores UCSD Cancer Prevention and Control Program, part of the University of California, San Diego.
The current analysis of the WHEL data did not look specifically at whether the women on the high fruit-and-veggie diet saw improvement in these other health areas. However, Stefanick says her group is presently looking into this question and expects to release information on one, if not more, subsets of the study group.
For now, she says, "Women should know that we expect to be able to identify a subgroup of breast cancer survivors who clearly do benefit from making these more intense changes in their diet and will report this once the data have undergone the important step of scientific peer review and approval." Furthermore, the final WINS data has not yet gone through this process either, she says, which means the fruit and vegetable jury may yet still be out on this issue.
Citation: "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." Published in the July 18, 2007, Journal of the American Medical Association (Vol. 298, No. 3: 289-298). First author: John P. Pierce, PhD, Moores UCSD Cancer Center, University of California, San Diego.