Compared to the United States and other Western countries, Asian countries are known to have lower rates of colorectal cancer. It has been suggested that one reason for this difference may be that Asian populations traditionally consume larger amounts of soy-based foods. However, studies of soy intake and colorectal cancer in humans have given mixed results.
Researchers in China recently conducted a very large-scale investigation of dietary soy and incidence of colorectal cancer in women (1). The Shanghai Women’s Health Study collected information from over 68,000 women, 40-70 years of age, and followed them for 2-3 years. The researchers studied demographics, dietary intake, medical history, family history, physical activity, and other lifestyle behaviors. After controlling for other factors that could influence cancer risk (age, calorie intake, physical activity, medical/family history, cigarette smoking, red meat intake, fruit and vegetable intake), postmenopausal women who ate more soy foods had a lower risk of colorectal cancer. In fact, for every additional 5 grams/day of soy food consumed, the risk decreased by 8%. This is approximately equal to the amount of soy in one ounce of tofu. It is important to note that this study focused on soy foods, not on soy isoflavone supplements. The results of this research suggest that regularly including soy foods in the diet may help protect women – particularly postmenopausal women – from developing colorectal cancer.
Yang G, Shu X-O, Li H, Chow W-H, Cai H, Zhang X, Gao Y-T, Zheng W. Prospective cohort study of soy food intake and colorectal cancer risk in women. Am J Clin Nutr 2009;89:577-83.