Background

Abbrevations listed at the bottom of this page 

Menopause is a period normally occupying one-third of women's life [1]. Reduced bone density is one of the most prominent symptoms during menopause [2].

Osteoporosis is a serious problem for postmenopausal women which increases the risk of bone fracture and worsens with age, increasing from 4% in 50–59 year age bracket to 50% in 80 years old women. Bone fractures are also prevalent in these women [3]. Today estrogen therapy (ERT) and drugs like bisphosphonates, calcitonin and raloxifene is employed to prevent and treat osteoporosis [4]. However, side effects such as breast cancer, endometrial adenocarcinoma [5] have limited the acceptance of these medications among women [6] and only 35% to 40% of women ever start ERT, and many do not continue it [7].

Epidemiologic studies have shown osteoporotic fractures, cardiovascular disease, postmenopausal symptoms and some cancers to be less prevalent in Asians compared to their western counterparts. Hip fracture, for example, is 50–60% less frequent among Asian compared to western women [8]. This advantage is gradually anihilated as Asian adapt western lifestyle [9]. These observations, prompted researchers to scrutinize Asian dietary habits. Soy is a part of Asian traditional diet [10], showing some relationship with the above-mentioned diseases [9].

Estrogen-like compounds such as isoflavones existing in plant foods specially soy [11,12] can curb reduced bone density in menopausal women, due to their structural similarity [13]. Some studies have not, however, supported clearly the role of soy isoflavones in preventing osteoporosis [14].

Isoflavones are phyto-estrogens similar to women's estrogens and are bound to cellular estrogen receptors in various organs, thus phytoestrogens affinity is weak compared to human's estrogens. Recent studies have shown that cells have two types estrogen receptors α and β. Human estrogens have more affinity to α-receptors, whereas, isoflavones have high affinity to β-receptors. β-receptors exist in brain, bone, bladder and vascular epithelium, being important in the function of non-steroid estrogens [15].

As soy cultivated in Iran is of different variety, namely "Gorgan" compared to other studies and because the Iranian food habits and food pattern is different [16] which might affect the metabolism of nutrients and isoflavones, this study was conducted to assess its effects compared to other countries. Furthermore there are still contradiction, in the literature regarding the role of soy isoflavones which justify implementation of this study.