December 12, 2014 | 4 minute read

A new long-term study that adds to the research on diet and breast cancer survival finds that women with certain types of breast tumors who reduced their dietary fat for years after diagnosis — and also lost weight — had lower death rates over the next 15 years than survivors on a standard diet.

The study was presented today at the San Antonio Breast Cancer Symposium and is not yet published in a journal.

It was funded in part by AICR and joins a growing body of research investigating how diet affects women diagnosed with breast cancer. In October, an AICR report on breast cancer survivorship in partnership with WCRF found some indication that fat may play a role in survival. The Continuous Update Project report found there was limited but consistent research suggesting that eating lower amounts of total fat and in particular, saturated fat, before a diagnosis of breast cancer linked to improved survival.

Weight loss may also play a role, as the low-fat group lost a a modest but significant amount of weight in this study. The CUP report found indications that being a healthy weight may lengthen survival for women diagnosed with breast cancer. But the report’s findings were not strong enough to make a specific recommendation.

Observational evidence relating to low-fat diets and breast cancer survival is mixed and previous research from another major randomized dietary study among breast cancer survivors – the WHEL study – found a lowfat diet did not affect mortality or recurrence.

The study presented today included approximately 2,400 women who were part of Women’s Intervention Nutrition Study (WINS), a study that first launched in 1987. All the women were diagnosed with early stage breast cancer and they joined the study within six months of diagnosis. About half of the women were asked to eat a low-fat diet for five years, consuming only 20 percent of their daily calories from fat. A standard diet averages about 35% of daily calories from fat.

An earlier WINS analysis back in 2006 found some evidence that women on the low fat diet may have lower risk of recurrence. Now, after 15 years, there was little difference overall in death rates between the women eating a low-fat and standard diet.

But when researchers separated out the women based on tumor type, they found lower death rates among the low-fat group of women who had tumors that grow without certain hormones. Women on the low fat diet who had tumors that were estrogen-receptor (ER) negative had a 36 percent lower risk of dying during the follow-up than those in the comparison group. The lower risk of death was even more pronounced among low-fat survivor women with tumors that were both ER negative and progesterone receptor (PR) negative.

Only the survivors on the low-fat diet lost weight, about 6 pounds, which may play an important role in survival. Weight loss reduces insulin levels and inflammatory factors, says study author Rowan T. Chlebowski, MD, PhD, an oncologist at the Los Angeles Biomedical Research Institute. “We really don’t know the mechanism.”

The survivors in the low-fat group lowered their fat calories by 9.2 percent. For a woman on a 2,000 calorie a day diet, that translates into cutting about a couple pats of butter or teaspoons of oil per day (about 8 grams of fat).

At a goal of 20% calories from fat, all categories of fat were reduced, notes Chlebowski. “All butter and spreads on bread would be out, and no oil based salad dressing were used.”

Long-term dietary studies are challenging, and even among the women who did reduce their fat intake, other dietary factors and/or weight could have played a role/

Along with AICR, the study was funded by the National Cancer Institute.

For the full analysis of the research on diet, physical activity and weight and breast cancer survivorship, here’s the findings of our Continuous Update Project Breast Cancer Survivorship report.  And our infographic.