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Soya protein boosts breast cancer survival chances

Soya protein boosts breast cancer survival chances
Women who have survived breast cancer have a better survival rate the more soya protein they consume. Chinese epidemiologists report on this in the Asian Pacific Journal of Cancer Prevention.

Soya protein boosts breast cancer survival chances

Attached to soya proteins are the isoflavones genistein, daidzein and glycitein. Their structural formulas are shown above. The ratio between the three compounds in 5:4:1. Isoflavones block the negative health effects of estradiol in the body.

One theory is that isoflavones are capable of attaching themselves to the beta-receptor for estradiol. When estradiol attaches itself to the receptor the body’s cholesterol improves, its bones become stronger and muscles recover. At the same time cells become less sensitive to the stimuli that estradiol emits through its alpha-receptor. Via this receptor estradiol stimulates fat deposition and the growth of some cancer cells.

So soya isoflavones have an oestrogenic and anti-oestrogenic effect. The anti-oestrogenic effect may explain why in many studies a high intake of foods containing soya reduces the likelihood of women developing breast cancer.

So maybe, surmised the researchers at the First Affiliated Hospital of Inner Mongolia Medical College in China, soya isoflavones and soya proteins protect women who already have breast cancer. To test this hypothesis they selected in 2004-2006 288 women with breast cancer and then monitored how many of them died in the period up to 2011.

The researchers got the participants to complete questionnaires to find out how much soya the women consumed in the form of foods such as tofu, soya milk, soya yogurt, soya ice cream, soya cheese, soya hot dogs, soya snacks, soya-based meat substitutes, tempeh, miso, soya beans, roasted soya nuts, soya sauce, soya bean sprouts, alfalfa and soya protein supplements.

The researchers divided the women on the basis of their soya consumption into four equal-sized groups or quartiles. The women in the quartile with the lowest intake consumed less than 4.5 g soya protein per day. The women in the quartile with the highest intake ate more than 14.8 g soya protein daily. The women in the latter group were 62 percent more likely to survive than the women in the first group.

Soya protein boosts breast cancer survival chances

Soya protein boosts breast cancer survival chances

The figure above shows the survival curves for all four quartiles. Click for a larger version. Of the women in the quartile with the lowest soya intake, 54 percent had died by 2011. In the quartile with the highest intake the figure was 19 percent.

The curves for the isoflavone intake are not much different: the more isoflavones the women consumed as a result of eating soya proteins, the higher their survival chances.

"The present study suggests soy intake is associated with a significant reduced death risk of breast cancer in Chinese population", the researchers conclude. "Further large sample studies are warranted to confirm the inverse association of soy consumption and breast cancer survival by menopausal status."

Asian Pac J Cancer Prev. 2012; 13(3): 995-8.

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