TUESDAY, Dec. 16, 2008 (Health.com) — Women who have been treated for early-stage breast cancer may have a lower risk of recurrence if they eat a relatively low-fat diet that's rich in fruits, vegetables, and fiber, according to a study published Monday in the Journal of Clinical Oncology.
However, this seems to be true only in women who don’t experience hot flashes when they start treatment. Hot flashes are a common side effect of breast cancer therapy; though uncomfortable, they are linked to a lower risk of breast cancer recurrence.
“Clinical symptoms of estrogen deprivation are hot flashes, so the women who don’t have hot flashes have higher estrogens,” says lead researcher John P. Pierce, PhD, head of cancer prevention at the Mores Cancer Center at the University of California, San Diego.
The new study is an analysis of a larger study called Women’s Healthy Eating and Living (WHEL). The 2007 WHEL study compared the effects of two diets on cancer recurrence in more than 3,000 early-stage breast cancer survivors. Some women ate an “intervention” diet, including five vegetable servings a day, 16 ounces of veggie juice, three fruit servings, and 30 grams of fiber. The other women were told to try to eat five servings of fruits and vegetables a day, but weren’t given any further instructions.
At the end of the five-year study, the researchers found no overall difference in breast cancer recurrence—even though the women in the intervention group consumed about half of the fat and had a 31% higher fiber and 54% higher intake of fruits and vegetables than other study subjects.
The research team then went back to see if there was a dietary benefit for any subgroup of women. They specifically looked at women who did not have hot flashes, who made up about one-third of the group.
They found that only 16.1% of women who did not have hot flashes at the study’s start had a breast cancer recurrence if they ate the intervention diet. In comparison, 23.6% of such women who ate a regular diet had a recurrence during a seven-year period. The dietary effect seemed to be even stronger for women who had been through menopause before the study started.
“We’ve known for a long time that, theoretically, diet influences breast cancer in some way,” says Julia A. Smith, MD, PhD, director of the NYU Cancer Institute's breast cancer screening and prevention program.
Estrogen is deposited and stored in body fat, so women who are overweight can have higher levels of estrogen than women who are not. However, it hasn’t been clear if changing the diet of breast cancer survivors can lower the risk of a recurrence, although curbing the body’s estrogen is a cornerstone of treatment for the majority of breast cancer types.
“Teasing it out has been difficult and I think that’s because breast cancer is not one disease, it’s multiple diseases,” says Dr. Smith. “I tell all my patients that we don’t have exact science or precise answers, but it’s important for women to pay attention to diet and keep their [body mass index] at a reasonable level.”
Pierce noted that the findings need to be confirmed in a trial where the intervention diet is the central hypothesis, not a side topic. More research is needed on other lifestyle changes for such women who are at high-risk for breast cancer and not responding to hormone therapy.
“If it’s an estrogen effect, well, that’s affected by physical activity as well as diet,” says Pierce. “It’s important that we study survivors because there are more than 2.5 million of them.”