X. Zhong and C. Zhang at School of Public Health, Sun Yat-Sen University in Guangzhou, China searched MEDLINE, Pubmed, EMBASE, Sci and CNKI databases and found 28 studies with 5 cohort studies and 23 case-control studies were eligible for the mata-analysis.
Overall, intake of soy food was inversely correlated with risk of breast cancer. An analysis of data from both types of study showed that those who ate high amounts of soybean products were 14 percent less likely to develop breast cancer, compared with those having a low intake.
The potentially protective effect against breast cancer was only observed in case-control studies, but not in cohort studies.
Also the protection against breast cancer was only found in studies conducted in Asian countries, but not in Western countries.
This observation may suggest that the amount of soy consumed in Western countries may be too little to have an effect. Asian women eat much more soy than Western women.
Also, the seemingly protective effect was only found in postmenopausal women. but not in premenopausal women.
The researchers concluded "According to the meta-analysis of studies conducted in Asian countries, soy food intake is inversely associated with the risk of breast cancer among Asian women, especially based on the results of meta-analysis of case-control studies."
