Older Chinese women who eat a Western-style diet loaded with meats and sweets have a greater risk for breast cancer than women who eat mainly soy and vegetables.
Previous research has found connections between a meat- and fat-heavy Western diet and several kinds of cancer, as well as heart disease and diabetes. And other research has identified links between obesity and cancer.
Researchers said this study signals a link between breast cancer and overall eating patterns - not a single food or nutrient - in Asian women, who have long had lower rates of the disease than Western women. But their numbers have started to rise as their diets have become more Westernized.
The study, which is not definitive, looked at general eating habits of about 3,000 women in Shanghai, ranging in age from 25 to 64. About half of that group had been diagnosed with breast cancer and are participants in an ongoing breast cancer study in Shanghai.
All the women were interviewed at length about their diets, answering questions about how often they ate 76 different items commonly found in Shanghai. Researchers then categorized the women into one of two dietary groups.
The "meat-sweet" group loaded up on red meat, shrimp, fish, candy, desserts, bread and milk. The "vegetable-soy" group stuck to tofu, vegetables, sprouts, beans, fish and soy milk.
Post-menopausal women in the meat-sweet group showed a 60 percent greater risk of developing the most common kind of breast cancer, the kind fueled by the hormone estrogen, compared to those in the vegetable-soy group, according to U.S. and Chinese researchers who conducted the study.
"We saw the clearest effect when we looked at post-menopausal women who were overweight, so it looks like there's an interaction between a meat-sweet diet and being overweight," said study co-author Marilyn Tseng, of Fox Chase Cancer Center in Philadelphia.
Researchers could not say how the combination of a Western diet and obesity might work in tandem to drive breast cancer.
The study, which appears in the journal Cancer Epidemiology, Biomarkers & Prevention, found no link, good or bad, between breast cancer and a vegetable-soy diet.
"This isn't a breakthrough, but it does add to the growing body of evidence that diet is related to breast cancer and other cancers," said Lawrence Cheskin, associate professor of international health and human nutrition at the John Hopkins Bloomberg School of Public Health, who was not connected to the study.
"We see a rise in cancers depending on what we're eating and if we're obese."
Tseng also said that the research should be a less frustrating guide for anybody looking to adopt sensible eating habits, instead of often contradictory research that names one vitamin, mineral or food as a cancer-quashing magic bullet.
"This gives us a broader sense because it looks at diet as a whole as opposed to targeting one element," Tseng said. "In terms of public health recommendations, that tends to give the wrong impression that you can reduce your risk of breast cancer by going after one specific component."