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Soya supplement doesn't make bones stronger

Older women with a sedentary western lifestyle won't maintain their bone mass by taking pills containing soya isoflavones, according to a three-year study from Iowa State University involving 224 women aged between 45 and 65.

Many studies have shown that soya inhibits bone breakdown in older menopausal women whose estradiol production has decreased. Nutritionists attribute this to isoflavones, phenols attached to the soya protein.

In test-tube studies the isoflavones attach themselves to the beta receptor for estradiol. Nearly all the positive effects of estradiol, such as improved cholesterol levels, bone growth and brain cell development, are the result of stimulating the beta receptor. Most of the negative effects of estradiol, such as an increased chance of some kinds of cancer, are related to a stimulus to the alpha receptor for estradiol. A stimulus to the beta receptor pretty much deactivates the alpha receptor.

That's why soya protein is a super food, to the annoyance of the meat and dairy industry. The American meat and dairy industry in particular are fighting a tough media campaign, claiming that soya has negative health effects, in the hope that this will persuade consumers to keep eating animal proteins.

The study in question here has nothing to do with that media offensive. It also says little about the health effects of whole soya products, such as soya milk, tahu or tempeh; it focuses instead on supplements containing soya isoflavones. According to the researchers, these do nothing to strengthen the skeleton. They gave 77 women 80 mg isoflavones daily and another 74 women 120 mg isoflavones. Three years later the researchers reported that the women in both groups had lost just as much bone mass as the women who had taken a placebo.

Soya supplement doesn't make bones stronger

The researchers don't exclude the possibility that higher doses of isoflavones may have a positive effect on bone mass. The bone mass in the hip decreased less in the women who took 120 mg isoflavones. But the effect was small.

Soya supplement doesn't make bones stronger

All the women who took part in the study also took 6 units of vitamin D3 and half a gram of calcium a day.

A Chinese study reported that the same doses of 80 and 120 mg isoflavones did work. [Eur J Nutr. 2006 Sep;45(6):327-34.] But Chinese women also get isoflavones from the food they consume daily, while Western women get hardly any. Perhaps higher doses of isoflavones are needed that the 80-120 mg/day used in the American study. Or perhaps supplements containing isoflavones only work if you also include whole soya products in your diet.

Am J Clin Nutr. 2010 Jan;91(1):218-30.

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