Postmenopausal Asian women who eat a Western diet at greater risk of developing breast cancer

Postmenopausal Asian women who eat a "meat-sweet" or Western diet are at greater risk of developing breast cancer than those who eat a "vegetable-soy" diet, according to a new study. The findings mark the first time an association between a Western diet and breast cancer has been identified in Asian women.

The study, published in the July issue of Cancer Epidemiology, Biomarkers & Prevention, involved women in the Shanghai Breast Cancer Study. Eligible cases included all women 25 to 64 years of age who with a new diagnosis of breast cancer from August 1996 to March 1998. Controls were selected from the Shanghai Resident Registry of permanent residents in urban Shanghai. "The issue [of diet] is of particular relevance to women in Asia, for whom breast cancer rates are traditionally low but increasing steadily in recent years," explained Marilyn Tseng, Ph.D., an associate member in the population science division at Fox Chase Cancer Center in Philadelphia.

The transition in breast cancer risk has been attributed to environmental factors, possibly the incorporation of Western dietary pattern foods into traditional dietary habits as a part of broader, societal socioeconomic changes. However, the association of dietary patterns with breast cancer risk has not been studied previously in Asian women.

Through in-person interviews with the Shanghai study participants and residents of Shanghai, researchers established the existence of two primary dietary patterns—the "meat-sweet" diet and a "vegetable-soy" diet. The "meat-sweet" diet includes various meats—primarily pork but also poultry, organ meats, beef and lamb and with saltwater fish, shrimp and other shellfish as well as candy, dessert, bread and milk. The "vegetable-soy" pattern is associated with different vegetables, soy-based products, and freshwater fish.

Of 1,602 eligible breast cancer cases identified during the study period, in-person interviews were completed for 1,459 (91.1%). In-person interviews were completed for 1,556 (90.3%) of the 1,724 eligible controls.

The "meat-sweet" pattern was significantly associated with increased risk of breast cancer among overweight postmenopausal women. Specifically, high intake of the "meat-sweet" pattern was associated with a greater than twofold increased risk of estrogen-receptor-positive (ER+) breast cancer among these women. The results showed no overall association of breast cancer risk with the "vegetable-soy" pattern.

"Our study suggests the possibility that the "meat-sweet" pattern increased breast cancer risk by increasing obesity, Tseng said. "Low consumption of a Western dietary pattern plus successful weight control may protect against breast cancer in a traditionally low-risk Asian population that is poised to more broadly adopt foods characteristic of Western societies."

Grants from the National Institutes of Health, the American Cancer Society, and the Commonwealth of Pennsylvania supported this research.

Tseng's co-authors include Xiaohui Cui at Fox Chase, a graduate student from the department of epidemiology of the Harvard School of Public Health; Yu-Tang Gao, M.D., from the Shanghai Cancer Institute; and Qi Dai, M.D., Ph.D., Xiao-Ou Shu, M.D., M.P.H., Ph.D., and Wei Zheng, M.D., Ph.D., M.P.H., from the School of Medicine and the Vanderbilt-Ingram Cancer Center at Vanderbilt University.