WASHINGTON Certain breast cancer survivors who load up on fruits and vegetables, eating far more than current U.S. guidelines, can slash their risk the tumors will come back by nearly a third, according to a U.S. study released on Monday.
The finding only held for women who did not have hot flashes after their cancer therapy, the researchers said -- a finding that suggests fruits and vegetables act on estrogen.
Their analysis suggests an explanation for why some studies have shown that eating more fruits and vegetables lowers the risk that breast cancer will come back, while others do not. It may depend on the individual patient, they report in the Journal of Clinical Oncology.
"Women with early stage breast cancer who have hot flashes have better survival and lower recurrence rates than women who don't," said Ellen Gold of the University of California Davis, who helped lead the study.
Several studies have shown this. And this study showed that women who had hot flashes after treatment for breast cancer had lower estrogen levels than women who did not.
As estrogen drives the most common type of breast cancer, this suggests that eating extra servings of fruits and vegetables -- above and beyond the five servings a day recommended by the U.S. government -- may lower harmful estrogen levels in cancer survivors, the researchers said.
"It appears that a dietary pattern high in fruits, vegetables and fiber, which has been shown to reduce circulating estrogen levels, may only be important among women with circulating estrogen levels above a certain threshold," said John Pierce of the University of California San Diego.
The researchers took a second look at data from 3,000 breast cancer patients in a study aimed at seeing whether a diet low in fat and high in fruits and vegetables might keep their cancer from coming back.
Such a diet has been shown to lower overall risk of ever getting breast cancer in the first place.
The women were on average 53, and half were told to double their fruit and vegetable intake to 10 servings a day, eat more fiber and lower fat intake more than government recommendations. "We compared the dietary intervention group to a group that received '5-a-day' dietary guidelines," the researchers wrote.
About 30 percent of the original 3,000 breast cancer survivors said they did not have hot flashes -- a common side-effect of breast cancer treatment.
The researchers looked at the data on these women specifically and found that only 16 percent of those who doubled up on fruits and vegetables had their tumors come back after seven years, compared to 23 percent of those merely given advice on food guidelines.
Women who had been through menopause lowered their risk by 47 percent if they loaded up on salads, fruit and other plant food.
(Reporting by Maggie Fox; Editing by Julie Steenhuysen)