Research cited in the American Journal of Clinical Nutrition indicates that soy intake reduces the risk of prostate cancer and breast cancer in men and women: Results from 14 studies show that increased intake of soy resulted in a 26% reduction in prostate cancer risk. Studies showed a 30% risk reduction with soy milk and tofu consumed (1)
Another study looked at the dietary patterns of approximately 2,400 Asian-American women. Those women with the highest intake of soy and vegetables had a decreased risk of breast cancer. Others with the highest intake of meat and starch had a two-fold increased risk. The researchers concluded that lower intake of meat and starch and higher intake of legumes and vegetables protects against breast cancer in Asian-American women. (2)
According to a recent report in the Journal of the American Medical Association, researchers found that women diagnosed with breast cancer who consume soy products, like soymilk, tofu, or edamame, have a 32% lower risk of recurrence and a 29% decreased risk of death, compared with women who consume little or no soy. This study included 5,042 women in the Shanghai Breast Cancer Survival Study, the largest population-based study of breast cancer survival. The researchers followed the study participants for a four-year period.
Many US physicians tell their patients who have or have had estrogen positive breast cancer to avoid all soy because soy contains phytoestrogens, plant estrogens.There are 3 kinds of phytoestrogens: isoflavones, lignans and coumestans. Isoflavones are found in soybeans and garbanzo beans. Lignans are in flax seeds and whole grain cereals and coumestans are present in sprouts (alfalfa, clover and soybean).
Isoflavones (in soy) are also antioxidants shown to reduce the initial risk of developing breast cancer. Concerns have been raised that isoflavones can promote re-growth of breast cancer by stimulating cell production. The authors wrote an accompanying editorial to the study suggesting that inconsistencies in prior research may be due to the comparatively low soy consumption in the United States and the high consumption of animal-based foods. This would make beneficial effects harder to identify. In China, soy intake is higher and diets include more traditional unprocessed sources of soy and few, if any, soy supplements. (3)
Healthcare professionals versed in plant-based eating advise women concerned with estrogen to lower their levels by consuming a high fiber (plant-based) diet. Fiber helps the body to eliminate excessive estrogen. Not getting enough daily fiber in your diet enables your body to re-absorb estrogen and can elevate your levels. Exercise and body fat reduction also lowers estrogen levels. In order to protect against a recurrence of breast cancer, attaining and maintaining proper body composition (more muscle than fat) along with a healthy plant-based diet and regular exercise are recommended.
(1)Yan L, Spitznagel EL. Soy consumption and prostate cancer risk in men: a revisit of a meta-analysis. Am J Clin Nutr. 2009;89:1155-1163.
(2) Wu AH, Yu MC, Tseng C, Stanczyk FZ, Pike MC. Dietary patterns and breast cancer risk in Asian-American women. Am J Clin Nutr. 2009;89:1145-1154
(3) Shu XO, Zheng Y, Cai H, et al. Soy food intake and breast cancer survival. JAMA. 2009;302:2437-2443.