Low-Fat Diet May Reduce Risk of Breast Cancer RelapseKey Words
Breast cancer, low-fat diet, prevention. (Definitions of many terms related to cancer can be found in the Cancer.gov Dictionary.)
Summary
Postmenopausal women who ate a low-fat diet were less likely to get a recurrence of breast cancer than those who ate a standard diet. This is the first time a large randomized clinical trial has shown that a low-fat diet can reduce the chance of breast cancer coming back.
Source
American Society of Clinical Oncology annual meeting, Orlando, Florida, May 16, 2005.
Background
Excluding nonmelanoma skin cancers, breast cancer is the most common cancer in women. It’s estimated that in 2005 more than 211,000 women in the United States will be diagnosed with invasive breast cancer. As a result of earlier detection and better initial treatments, more women are surviving an initial diagnosis of breast cancer, but many of them remain at risk for a recurrence.
Many studies in animals, as well as observational studies in humans, have strongly suggested that a high-fat diet contributes to the development of breast cancer in postmenopausal women. Subsequent large prospective studies, however, have failed to show that lowering dietary fat led to a reduction in breast cancer risk.
The Study
The Women's Intervention Nutrition Study (WINS) was a large, prospective, randomized phase III study to investigate whether a low-fat diet could reduce breast cancer recurrence rates in postmenopausal women who had been treated for early-stage breast cancer. Postmenopausal women were chosen because they tend to have less variability in their types of breast cancer than premenopausal women.
Between 1994 and 2001, the study enrolled 2,437 women who in the previous year had had breast cancer surgery followed by therapy appropriate to their particular cancer. The women, whose average age was 62 were randomly assigned to one of two dietary groups. One group was asked to follow their standard diet. Women in this group met with a nutritional counselor periodically but were not urged to change their diet, which contained an average of about 51 grams of fat a day (about 40 percent of total calories from fat).
Women in the second group were asked to modify their diet to reduce their consumption of dietary fat to 20 percent of total calories. Each woman received eight one-on-one dietary counseling sessions with a nutritionist (one every other week for 16 weeks). After that, they saw the nutritionist every three months for the duration of the study. The nutritionist offered support and advice about reducing dietary fat consumption by, for example, using less oil when cooking, increasing intake of fruit and vegetables, controlling portion sizes, and so on. The diet eaten by women in the low-fat group contained an average of 33 grams of fat a day.
Women in both groups kept diaries in which they recorded their daily food consumption. In addition, trained interviewers periodically contacted all of the women by phone to question them about what they were eating.
Encouraging women to have more active lifestyles was not a goal of the study, said principal investigator Rowan T. Chlebowski, M.D., Ph.D, of the Los Angeles Biomedical Research Institute in California. Most women in both the standard-diet and low-fat diet groups had sedentary lifestyles.
Results
After a median of five years of follow-up, breast cancer had come back in 9.8 percent of the women on the low-fat diet and 12.4 percent of those on the standard diet. This amounted to a 24 percent reduction in the risk of recurrence for the women on the low-fat diet.
The largest risk reduction - 42 percent - was seen among women on the low-fat diet whose tumors did not respond to the presence of the hormone estrogen. Breast cancer that doesn’t respond to estrogen is called estrogen receptor negative (ER-negative) and usually has a poorer outlook than ER-positive disease. Postmenopausal women whose tumors do respond to estrogen are candidates for anti-estrogen drugs such as tamoxifen or letrozole, which help reduce the risk of relapse.
Although weight loss was not a goal of the study, women who followed the low-fat diet lost an average of four pounds, said Chlebowski.
(Note: final results from this study were subsequently published in the Dec. 20, 2006, Journal of the National Cancer Institute; see the journal abstract and the related NCI press release.)
Limitations
The research team cannot be certain that the low-fat diet was responsible for the lower rate of recurrence in the women assigned to that group, said Chlebowski. Other factors, such as the modest weight loss seen in the low-fat group or increased consumption of fruit and vegetables, may have contributed to the outcome.
Additionally, some, but not all, women in both study groups were treated with chemotherapy following surgery. The researchers have not yet analyzed whether chemotherapy was associated with improved survival.
Comments
These results suggest that an intervention aimed at reducing dietary fat consumption can reduce the risk of breast cancer recurrence, said Chlebowski. Although further confirmation is needed, he said a low-fat diet may offer other health benefits, such as modest weight loss.
It may be reasonable for physicians to suggest that postmenopausal women who have been treated for breast cancer consider following a low-fat diet because of these other health benefits, he concluded.
“This is one of the very few controlled intervention studies [in the field of cancer prevention] where we can truly monitor the efficacy of the intervention,” said John Milner, Ph.D., of the National Cancer Institute’s Division of Cancer Prevention. “Monitoring was done every three months, which is far better than in many trials. I have a lot of faith in this study.”
Milner also noted that “we have few options to offer women with ER-negative tumors” in terms of preventing a recurrence of their cancer, and so this study’s suggestion that a low-fat diet may be particularly effective for them “is exciting news.”
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