July 10, 2007 -- A diet rich in meats and sweets can boost the risk of breast cancer in older women by 60% or more compared with a diet rich in vegetables, soy, and fresh fish, a new study of Asian women shows.
Breast cancer rates are typically low among Asian women, but as their breast cancer rates have climbed steadily in recent years, experts have begun to focus on the effect that adopting Western eating habits has on Asians. "There is a hypothesis that a Western diet increases the risk of breast cancer," Marilyn Tseng, PhD, a study co-author, tells WebMD.
So her team carefully evaluated the diets of 1,459 breast cancer patients and 1,556 healthy women in Shanghai to see if they could find a link between diet and breast cancer risk. "It's the first time a Western diet pattern has been linked with breast cancer in Asian women," says Tseng, an associate professor in the population science division at Fox Chase Cancer Center in Philadelphia. The effect held true only for the older women.
Tseng and her colleague interviewed Shanghai breast cancer patients and Shanghai residents in depth about their eating habits over the past five years. Women with breast cancer had been diagnosed from August 1996 through March 1998. The women in the comparison group were selected from the Shanghai Resident Registry of permanent residents of urban Shanghai. The average age was 47 in each group.
The researchers uncovered two general dietary patterns. The “meat-sweet” diet included various meats, mainly pork but also poultry, organ meats, beef, lamb, saltwater fish, and shrimp along with candy, desserts, breads, and milk. The "vegetable-soy" diet was filled with various vegetables, soy-based products, and freshwater fish.
"What we found was the meat-sweet diet actually did increase the risk for breast cancer," Tseng tells WebMD. The vegetable-soy diet wasn't found to protect against breast cancer.
"We did not see a significant effect [of dietary patterns] on premenopausal women, we saw it only in postmenopausal women," says Tseng. The study is in the July issue of Cancer Epidemiology, Biomarkers & Prevention.
"A meat-sweet diet raised the risk [of breast cancer] by 60% in postmenopausal women," Tseng says. Among women who were postmenopausal and overweight, with a body mass index of 25 and greater, Tseng's team found a more than twofold increased risk of getting a specific type of breast cancer, called estrogen-receptor positive, if they ate the highest amounts of a meat-sweet diet compared with the vegetable-soy one. Estrogen-receptor positive breast cancer is typically less aggressive than estrogen-receptor negative breast cancer.
The meat-sweet pattern may have increased the risk of breast cancer by increasing obesity, she says.
Other Experts Weigh In
Looking at dietary patterns, not just individual foods, is an area of emerging research for diet and breast cancer links, says Anna Wu, PhD, professor of preventive medicine in the division of epidemiology at the Keck School of Medicine at the University of Southern California, Los Angeles.
"Studies of dietary patterns and breast cancer started around 2000," she tells WebMD. "Prior to that, researchers tended to focus on individual foods or food groups or macro and micronutrients."
The research is complicated, however, by the fact that different researchers define a Western diet in different ways, she says.
"Using dietary patterns is a reasonable way to investigate links between diet and breast cancer," says another expert, Teresa Fung, ScD, RD, associate professor in the department of nutrition at Simmons College in Boston. Fung researches the nutritional roots of chronic diseases.
"The link between various diet components (for example, nutrients and foods) and breast cancer is quite inconsistent except for alcohol [and being overweight]," she says. "However, the meat-sweet pattern is similar to the Western pattern that is seen in other studies. And that Western pattern has been associated with colon cancer, type 2 diabetes, and heart disease."
Take-Home Points, for Now
More research is needed on the diet-breast cancer link, experts agree. But for now, says Fung, "it would be prudent at the minimum to stay away from a diet heavy in meat, processed grains, sweets, and desserts." Instead, she suggest, adopt a diet abundant in minimally processed plant foods (not necessarily a vegetarian diet), which have been associated with many health benefits."
"I think definitely women in Asia should be cautious about embracing a Western style diet," Tseng says. "In this country, I think women should be careful about foods that fall into that pattern. For all women, weight control is probably in order."