Soy Protein Benefits

Table hereunder lists the death rates from breast cancers in selected Eastern and Western countries.

Death Rates Per 100,000 Population For Breast Cancer

	Country	Breast Cancer
	Western Nations
	United States	21.1
	United Kingdom	26.5
	Germany	22.1
	Eastern Nations
	Japan	6.8
	China	5.0

The existing data from epidemiological studies, along with supportive data from animal studies, strongly support the concept that consumption of soy protein may reduce the risk of certain cancers in humans. Researchers who are studying the possible role of soy protein in cancer prevention have focused primarily on tumors known to be affected by hormones and diet. Research on soy protein and breast cancer prevention is one of the most active research areas today.

Soy Protein and Breast Cancer
Findings from recently completed epidemiological studies conducted in China (Dai et al., 2001; Shu et al., 2001) and an ongoing study in the U.S. (Wu et al., 2001) demonstrated that consumption of soyfoods during adolescence and adulthood results in a reduction in the incidence of breast cancer in women. These results support the existing knowledge from previously published epidemiological investigations that consumption of soy is beneficial in reducing the risk of breast cancer in women.

Results from animal studies support epidemiological findings. Feeding female rats a diet that contained isolated soy protein inhibits experimentally induced mammary tumor development compared with rats fed a casein-based diet (Barnes et al., 1994; Hawrylewicz et al., 1991). Hakkak et al (Hakkak et al., 2000) investigated the effect of long-term feeding animals a diet containing isolated soy protein on mammary tumor development.

They fed rats a soy protein-containing diet or a casein-based diet for two generations before administering a chemical agent known to induce mammary tumor to the third generation. At the end of the study, there was a significant decrease in the number of mammary tumors and a significant increase in the latency period in rats maintained on the soy protein diet compared with those on the casein diet.

Constantinou et al (Constantinou et al., 2001) examined the synergetic effect of isolated soy protein with tamoxifen on chemically induced mammary tumor development in rats. Tamoxifen is a drug approved by the U.S. FDA for breast cancer prevention in humans. They found that dietary supplementation with isolated soy protein or tamoxifen resulted in a 37% or a 29% reduction in the number of tumors developed in mammary glands compared with the controls.

However, they found a 62% reduction in the number of tumors in the group fed a diet containing both soy protein and tamoxifen compared with the controls. Results from this study showed that soy protein is synergetic with tamoxifen and resulted in a greater inhibition on chemically induced mammary tumor development in animals. It suggests that consumption of soy protein is beneficial to women who use tamoxifen for breast cancer prevention.

Yan et al (Yan et al., 2000) investigated whether dietary supplementation with isolated soy protein reduced pulmonary metastasis of malignant cells from mammary tumors in mice. The spread of cancerous cells from a mammary tumor to the lungs and other organs in the body is a major cause of death in breast cancer patients. Mice were fed a casein-based control diet or a diet supplemented with different contents of isolated soy protein before receiving an injection of mammary tumor cells into mammary glands for primary tumor development.

At the end of the study, the number of tumors formed in the lungs were counted as a measurement of the cancer spread because the more malignant cells spread to the lungs and the more tumors could be developed. The researchers found that there was a significant reduction in the number of metastatic tumors formed in the lungs in mice fed the soy protein diets compared with those maintained on the control diet.

These results demonstrated that soy protein reduced the spread of mammary cancer in animals, suggesting that soy protein is a useful nutritional adjutant in reducing metastasis in breast cancer patients.

Many researchers have investigated the role of genistein, a major soy isoflavone, in mammary tumor development in animals. Fritz et al (Fritz et al., 1998) examined the effect of dietary supplementation of genistein on chemically induced mammary tumorigenesis in rats. Female rats were fed a diet containing different levels of genistein from conception to day 21 post-parturition.

All offspring were weaned at the age of 21 days, maintained on a genistein-free diet, and treated with a cancer-causing agent to induce mammary tumors at the age of 50 days. At the end of the study, animals from mothers fed genistein-supplemented diets had fewer mammary tumors compared with those from mothers fed a genistein-free control diet.

Similar inhibitory effect on mammary tumor development has also been observed when genistein was subcutaneously injected into animals (Murrill et al., 1996; Lamartiniere et al., 1995). Results from these studies suggest that genistein is, at least in part, responsible for the cancer-attenuating effect of soy protein products.

The important thing to keep in mind is that soy isoflavones are chemically similar to naturally occurring and synthetic forms of estrogen. They are able to compete with more potent forms of estrogen at the estrogen receptor but have much less estrogenic activity. Research suggests that soy isoflavones are able to mimic some of estrogen's functions, such as helping prevent bone loss, but may not stimulate the unfavorable responses in breast tissue that may increase the risk of cancer.

This reduced risk of breast cancer doesn't appear to be genetic since it disappears as Asian women move to the West. One study found that in Chinese and Japanese women, the incidence of breast cancer was lowest in those living in Asia, intermediate in those born in Asia but living in the United States, and highest in Asian women born in the United States. Even in this last group, the incidence of breast cancer was appreciably lower than in American Caucasian women.

References
View cancer references list.