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Q: Should I Eat Soy? Part 4
A: Amid some of the negative articles that have been published about soy, I continue to recommend it as a great plant source of protein that is heart healthy and most likely confers some protective effects for women wanting to reduce their risk of breast cancer. I consume it every day myself.
The following 2 studies document my claim that soy products may reduce the risk of breast cancer and that consumption of soy may account for the lower rate of breast cancer among Asian women.
In 1996, Wu et al conducted a case-controlled study of breast cancer risk in Asian women in the U.S. Controls were matched on age, ethnicity and area of residence. Dietary information was gathered in an in-person interview. Asian American women born in Asia ate tofu more than twice as often as those born in the U.S. In both pre- and post- menopausal women the risk of breast cancer decreased with increased frequency of tofu ingestion.
In order to understand the next study, you need to understand the mechanism of action of phytoestrogens. In plants, phytoestrogens are present in glycoside form. The metabolism of phytoestrogens increases their potency. The hydrolysis of glucoside to aglucone occurs in the colon. The aglucone then either undergoes fermentation by gut flora or conjugation in the liver. A proportion is excreted in bile and then circulates throughout the body. The primary route of excretion is through the urine with a half- life of less than 24 hours.
In 1997, Ingram et al carried out a study in Australia to assess the association between phytoestrogen intake and risk of breast cancer by measuring urinary excretion of phytoestrogens over 72 hours. Women with newly diagnosed breast cancer were pared with controls matched for age and area of residence. After adjustments were made for confounding variables, those with the highest 25% of excretion of phytoestrogens had a 3-4 times decrease in breast cancer risk than those in the lowest 25%. (Lancet 1997)
Although these studies are limited in size and scope, they do offer some explanation of why Asian women are experiencing lower rates of breast cancer than American carnivorous women.
However, it is important to remember that Asians eat a low-fat, plant based diet, and it is likely that the combination of the healthy diet, as well as its individual foods such as soy that confer the protective effect.