Health experts have long touted the benefits of a low-fat diet for preventing heart disease, but now a large study suggests it might do the same against breast cancer.
Researchers found that eating low-fat foods reduced a woman's risk of dying from breast cancer by 21%. What's more, the women on low-fat diets also cut their risk of dying from any cause by 15%.
"This is the only study providing randomized controlled trial evidence that a dietary intervention can reduce women's risk of death from breast cancer," said study author Dr. Rowan Chlebowski. He is from the Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center in Torrance, Calif.
Diet has long been suspected to be a factor in cancer. Obesity has been linked to 12 different types of cancers, including postmenopausal breast cancer, according to the American Institute for Cancer Research. And, a diet full of healthy foods, such as vegetables, fruits, whole grains and legumes is thought to help protect against cancer.
Chlebowski noted that previous studies have shown a higher cancer incidence in countries where people tend to eat more fat.
The latest study looked at the effect a low-fat diet might have on the incidence of breast cancer and death.
Nearly 49,000 postmenopausal women from 40 centers across the United States were included in the study. The women were between the ages of 50 and 79, and had no history of previous breast cancer. Eighty percent of the women were white, which Chlebowski said matched the population when the study began.
Between 1993 and 1998, the women were randomly assigned to one of two dietary groups. One group was assigned to a normal diet. This diet had about 32% of their calories from fat. The low-fat group had a target of 20% or less of calories from fat.
Chlebowski said the low-fat diet was close in content to the Dietary Approaches to Stopping Hypertension (DASH) diet. This emphasizes eating vegetables, fruits, legumes and whole grains, while avoiding high-fat meats and dairy products, according to the U.S. National Heart, Lung, and Blood Institute.
The low-fat group lost a modest amount of weight. Chlebowski said there was about a 3% difference in weight between the groups. He said the researchers factored the weight difference into their calculations and that weight alone didn't affect the risk of death.
Women in the low-fat group adhered to the diet for about 8.5 years, and both groups were followed for an average of nearly 20 years.
The women in the low-fat group weren't able to achieve the 20%-or-less target for fat, but they did manage around 25%, according to the researchers. And they did increase their intake of fruits, vegetables and grains.
"The diet was more moderate than originally planned. But we saw a diet of 25% to 27% fat is largely achievable," Chlebowski said.
He said the researchers don't know if any individual components of the diet were more important than others, but they hope further study will tease that out.
In the meantime, Chlebowski said he thinks the message should be one of dietary moderation rather than looking for any one particular food or food group. He said the women in the low-fat study group reduced their overall calories, changed their cooking methods, and reduced their portions of meat and dairy products.
The findings are to be presented at the American Society of Clinical Oncology (ASCO) annual meeting, in Chicago, from May 31 to June 4. Findings presented at meetings are typically viewed as preliminary until they've been published in a peer-reviewed journal.
ASCO breast cancer expert Dr. Lidia Schapira, from Stanford University, noted that this study shows "what we put on the plate matters. It's worth coaching and pushing patients to put more fruits and vegetables on their plates."
She added that even when women didn't reach the more stringent dietary fat goal of 20%, they still showed a health advantage from trying to reduce the fat in their diets.
Dr. Monica Bertagnolli, president of ASCO, said these findings were "really, really striking."
She noted, "This was not an incredibly restrictive diet. People were able to adhere to it pretty well."
And yet, the incidence of breast cancer went down by 8% in the women on low-fat diets.
"They were getting fewer breast cancers, and even when they did get breast cancer, their death rate was reduced," Bertagnolli said.
Wondering how your own diet might stack up for cancer prevention? Find out with this quick quiz on healthy eating from the American Institute for Cancer Research.