Extra fruits, vegetables in diet does not stop breast cancer return

19 July, 2007:

A diet low in fat and high in fruits and vegetables may not necessarily prevent the return of breast cancer.

A large, seven-year experiment involving over 3,000 women, commissioned by the United States government, found no benefit from an extra-large diet of vegetables and fruits over the US-recommended servings of five fruits and vegetables a day – which is more than what most Americans get.

Canada’s Food Guide recommends 7 to 10 servings a day for adults between 19 and 50 years of age.

Researchers noted that none of the survivors of breast cancer lost weight on either diet, leading some experts to suggest that weight loss and exercise should be the next frontier for cancer prevention research.

The study appears in the July 18, 2007, issue of the Journal of the American Medical Association.

“It sends us back to the drawing board,” says Susan Gapstur of Northwestern University’s Feinberg School of Medicine, who was not involved in the new study, but co-wrote an accompanying editorial in the journal.

For now, the message for breast cancer survivors is that they do not need to eat too much vegetables and fruits, researchers said.

The research was started by a $5-million US grant from John Walton, the late heir of Wal-Mart, and an additional $30 million from the National Cancer Institute.

Earlier research on whether a healthy diet prevents breast cancer has shown mixed results. The new study was designed to be more rigorous.

In this experiment, all the women had been successfully treated for early-stage breast cancer. Their average age was 53 when the study began.

In one group, 1,537 women were randomly assigned to a daily diet that included five vegetable servings, three fruit servings, 16 ounces (about 500 ml) of vegetable juice and 30 grams of fibre. In most cases, a serving equalled a half-cup (125 ml). French fries and iceberg lettuce could not be counted as vegetables.

The women were allowed to eat meat, but were told to get no more than 15% to 20% of their calories from fat, a goal they ultimately were unable to achieve.

As a comparison, another 1,551 women were assigned to get educational materials about the importance of eating five servings of fruits and vegetables a day.

The women in both groups kept food diaries regularly, but not daily, throughout the study.

During the next seven years, the cancer returned in about the same proportion of women in both groups – 256 women (16.7%) of the women on the special diet and 262 women (16.9%) in the comparison group. During that time, about 10% of the subjects in both groups died, most of them from breast cancer.

According to the researchers, it did not matter whether the breast cancer was the most common type – fueled by hormones – or not; the special diet did not prevent the cancer from returning. The results run counter to a previous study by different researchers that suggested low-fat diets may help prevent the return of the type of breast cancer that is not linked to hormones.