There are many reasons women should eat a healthy diet, but for breast cancer, there is little evidence that the foods you eat impact risk.
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 that all breast cancer survivors should know, watching your weight is really important.
A 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 seven other institutions. The participants were more than 3,000 women, pre- and post-menopausal, who had been treated for stage I, II, or III breast cancer.
The women were randomly assigned to two diet groups: The control group was told to follow U.S. dietary guidelines, which recommend eating at least five 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 five vegetables, three 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 seven years on average. They saw clear differences in the amount of fruits and vegetables the women in the two groups ate, although after year four of the study, the gap between the two 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, and in fact, by year six, they were eating a higher percentage of fat than at the beginning of the study.
Despite the difference in fruit and vegetable consumption, the two groups had very similar cancer experiences during the seven years. About 17% of women in each group had a recurrence during the study period, and about 10% of women in each group died.
But it may be that diet is important in the context of weight control. For instance, the 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. 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! Fruits and vegetables are packed with nutrients and low in calories, and more evidence suggests they can help with weight control.
Plus, other studies have shown that eating more than five a day can reduce the risk of heart disease and stroke, and can help keep blood pressure under control. 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.
For now, women should know that we hope 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, which means the fruit and vegetable jury may yet still be out on this issue.
Dr. C. Joseph Bennett is a board-certified radiation oncologist. If you have any suggestions for topics, or have any questions, contact him at 522 N. Lecanto Highway, Lecanto, FL 34461, or email him at email@example.com.