Soy is a native to Asia and contains plant estrogen called phytoestorgens that can benefit your bones. Thinning of bone tissue increases the risk of developing age-associated osteoporosis and hip fracture rates, especially in women. Estrogen spares calcium and promotes bone mineral density, adding soy into your diet can help preserve your bone density.
Soy isoflavones are the active phytoestrogen that mimics the effects of estrogen produced by your body. Soy isoflavones seem to decrease calcium loss through the urine compared to animal protein sources. Animal proteins increase calcium loss through the urine. Asian women consuming a high soy diet have a lower rate of hip fractures than Western women that consume a diet high in animal proteins (1). Animal proteins increase the acidity of urine and your body responds by releasing calcium from your bones to neutralize your urine. Increasing your soy protein intake may help increase the alkalinity of your urine, thereby decreasing the amount of calcium released to neutralize the acidity of your urine.
Menopause can cause a 15 percent loss in bone mineral density, especially during the first 5 years (1). Women of childbearing age have higher estrogen levels than postmenopausal women and have the least benefit of isoflavones from soy in protecting bone mineral density. Isoflavones act like estrogen and seem to provided the greatest benefit when your body levels are below normal (2). Higher bone densities of the hip and spine were seen in postmenopausal females with the addition of soy.
Soy proteins are rich in genistein, which is the most abundant isoflavone found in soy foods. Genistein promotes bone formation in postmenopausal women (2). Genistein seems to slow down the activity of the osteoclasts or bone cells that break down bone tissue. Osteoclasts work by removing calcium from bone that isn’t needed, so the calcium can be used elsewhere in your body. Decreasing their activity helps to preserve bone density because less calcium is being taken out of your bones than what is being deposited.
Soy protein isn’t a cure for osteoporosis. The benefit to your bones is negated if your diet is low in dietary calcium. Insufficient calcium intakes limits soy’s ability to protect your bones. Reaching the recommended daily allowance of calcium and vitamin D, 1,000 mg and 400 IU, respectively, enhances soy’s benefits for your bones. Adding soy to your diet, along with consuming foods rich in calcium and vitamin D have a synergistic affect on your bone health.
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