How are soy products connected to breast cancer?

Answer 1

Recent articles have touted the virtues of eating soy products to reduce the risk of breast cancer, but experts say the effects are still unknown and that consuming soy may actually increase breast cancer risk for some women.
Studies have shown Asian women have a breast cancer rate one-fifth that of Western women, and some research suggests the lower rates are linked to consumption of soy, a staple of the Asian diet.

Soy is high in phytoestrogens, natural chemicals found in plants that act like weak forms of the estrogens naturally produced in a woman's body. It is especially high in the phytoestrogen, isoflavone, which contains two important compounds -- genistein and daidzin.

Understanding the Effects of Phytoestrogens
The effects of phytoestrogens on a woman's body are not fully understood, but it is believed they compete with estrogen to fit into estrogen receptor sites in different parts of the body, including breast tissue. Because estrogen stimulates cell reproduction, it may be that the more exposure a women has to estrogen, the greater her breast cancer risk. In premenopausal women, phytoestrogens may have an estrogen-reducing effect because they attach to estrogen receptor sites, thus tricking the body into producing less estrogen.

The effect of phytoestrogens is less clearly understood in postmenopausal women, whose estrogen levels are naturally lowered. Although there is some evidence to suggest consumption of soy reduces breast cancer risk in premenopausal women, there is no evidence that consumption of soy reduces postmenopausal breast cancer risk. Some doctors and nutrition experts believe phytoestrogens may actually boost estrogen levels in postmenopausal women.

Currently, no clinical trials have shown eating specified amounts of soy products over time reduces the risk of breast cancer. Animal studies and in vitro (test tube) studies of cancer tissue point to a connection between isoflavonoids and reduced breast cancer risk, but no causal relationship has been established.

"There is no clear-cut evidence on the advantages or disadvantages of increased levels of isoflavonoids in the prevention of breast cancer," said Kathryn Hamilton, MA, RD, clinical nutrition manager at Memorial Sloan-Kettering's Breast Oncology Department. "Until we figure out what kind of estrogens fuel breast cancer, no one should be self-prescribing or self-diagnosing."

Answer 2

Certain scientific studies have found that increased levels of estrogen hormone increase the risk of breast cancer.

Soy contains phyto-estrogen, which acts like regular estrogen in your body, which in turn, can increase your risk for breast cancer.

If you are worried, just limit your intake of soy products -- but there is no need to eliminate them all together.

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Answer 3

They change the hormone levels --"Soybean products, including soy oil, block iodine uptake. Your thyroid gland cannot function properly without iodine. Symptoms of low thyroid function include fatigue, dry skin and hair, cold hands and feet. Other iodine blockers include fluoride and chlorine. Other foods that block iodine uptake include raw kale, turnips, broccoli, cauliflower and cabbage, but once you cook them they’re fine. For more details, please read Chapters 4 (about thyroid) and Chapter 16 (about soy) in What Your Doctor May Not Tell You About Breast Cancer."