SOURCES: Maryam Farvid, Ph.D., department of nutrition, Harvard School of Public Health, Boston; Stephanie Bernik, M.D., chief of surgical oncology, Lenox Hill Hospital, New York City; Betsy Booren, Ph.D., vice president of scientific affairs, American Meat Institute Foundation; David Katz, M.D., M.P.H., director, Yale University Prevention Research Center, New Haven, Conn.; June 10, 2014, BMJ, online
TUESDAY, June 10, 2014 (HealthDay News) -- Women who ate the most red meat increased their risk for breast cancer by nearly 25 percent, a 20-year study of nearly 89,000 women suggests.
On the flip side, however, replacing a daily serving of red meat with a combination of fish, legumes, nuts and poultry appeared to lower the risk of breast cancer by 14 percent, the researchers said.
"Cutting down processed meat, limiting intake of red meat, and substituting a combination of poultry, fish, legumes and nuts as protein sources for red meat during early life seems beneficial for the prevention of breast cancer," said lead researcher Maryam Farvid, who's with the Harvard School of Public Health's Department of Nutrition.
Compared with women who had one serving of red meat a week, those who ate 1.5 servings a day appeared to have a 22 percent higher risk of breast cancer. And each additional daily serving of red meat seemed to increase the risk of breast cancer another 13 percent, Farvid said.
Eating more poultry, however, lowered the risk, the researchers noted. Substituting one serving a day of poultry for one serving a day of red meat reduced the risk of breast cancer by 17 percent overall and by 24 percent among postmenopausal women, the researchers found.
"Decreasing consumption of red meat and replacing it with other healthy dietary sources of protein, such as chicken, turkey, fish, beans, lentils, peas and nuts, may have important public health implications," she said.
"Reduction of red meat intake in the diet not only decreases the risk of breast cancer but also decreases the risk of other chronic diseases, such as coronary heart disease, stroke, diabetes and other kind of cancers, as well," Farvid said.
Because this is a so-called observational study, it doesn't prove that more red meat increases breast cancer risk. And the biological reasons behind the apparent red meat-breast cancer connection isn't clear, she said.
A representative of the meat industry took issue with the findings.
"As several researchers who have analyzed this study have already pointed out, the totality of the available evidence indicates that red meat consumption has little or no effect on breast cancer risk," said Betsy Booren, vice president of scientific affairs at the American Meat Institute Foundation.
"This study, with extremely weak associations based on self-reported food intake, doesn't add much to our current knowledge on this complex condition," she added.
However, Farvid said that red meat has been thought to increase the risk of breast cancer in different ways. Cancer-causing "byproducts created during high temperature cooking of red meat" may be to blame, she said. Another possibility: hormones used to increase growth of beef cattle. Also, she noted, "food preservatives such as nitrate and nitrite in processed meat can also be associated with elevated risk of breast cancer."
The report was published June 10 online in the BMJ.
For the study, Farvid and her colleagues collected data on almost 89,000 women, aged 26 to 45, who took part in the Nurses' Health Study II. The women completed a questionnaire on diet in 1991, 1995, 1999, 2003 and 2007, according to the study.
Participants were asked about daily consumption of unprocessed red meat, such as beef, pork, lamb and hamburger, and processed red meat, such as hot dogs, bacon and sausage.
They were also asked how much poultry (including chicken and turkey); fish (including tuna, salmon, mackerel and sardines) and legumes (including beans, lentils, peas and nuts) -- they ate each day. The responses were ranked from "never or less than once per month" to "six or more per day."
Over 20 years of follow-up 2,830 women developed breast cancer, according to the study.
To try to determine red meat's role in the risk for breast cancer, Farvid's group also factored in differences in height, weight, race, family history of breast cancer, history of benign breast disease, smoking, menopausal status, hormone and oral contraceptive use. They also took into account the participants' diets when they were teens.
"This paper very usefully translates findings about the associations between meat intake and breast cancer risk into specific, actionable, risk-reducing strategies," said Dr. David Katz, director of the Yale University Prevention Research Center.
"In general, replacing one daily serving of meat with legumes, fish or poultry has the potential to reduce breast cancer risk by a relative 15 to 20 percent. That is clearly enough to matter," said Katz.
But not everyone agreed that the study's findings were conclusive.
Dr. Stephanie Bernik, chief of surgical oncology at Lenox Hill Hospital in New York City, said the study wasn't "definitive."
"The women who ate less red meat may have a healthier lifestyle, and that reduces their risk of cancer. The increased risk tied to red meat might only stand in for other unhealthy behaviors," she said. "A healthy lifestyle can lower your risk of cancer in general."
However, Bernik noted that eating a lot of red meat has been linked to an increased risk of other cancers, such as colon and prostate cancer.
For more information on breast cancer, visit the American Cancer Society.