ABSTRACT
Osteoporosis is gradual declining of bone mass with aging, leading to increased bone fragility and fractures. The incidence of osteoporosis is increasing worldwide especially in Asian countries. Fractures of hip and spine are known to be the most important complication of the condition, resulting in 20% annual mortality and 50% serious morbidity. Menopause is one of the most common risk factors of osteoporosis. After menopause, sex hormone decline causes increased bone remodeling and negative bone balance, leading to accelerated bone loss and micro-architectural defects which brings about increased bone fragility. Estrogen-like compounds like [isoflavones] present in plants especially soy may reduce bone loss in postmenopausal women as they are similar in structure to estrogens. This review study was conducted to survey articles regarding the role of phytoestrogens in preventing menopausal osteoporosis. Published articles from 1990 to 2005 were searched by using Medline and selected with appropriate key words. The mechanism by which phytoestrogens reduce bone mass declining lies in their weak estrogenic properties and their effects on estrogen receptors, so that they can act as human estrogens in a prolonged period. According to research and hypotheses existing about the effects of phytoestrogens on postmenopausal osteoporosis suppression, intake of 90 milligram [30-40 gr soy protein contains 90 mg isoflavones] or more isoflavones per day for at least 12 weeks can positively influence on the reduction of bone resorption markers and the improvement of bone formation markers in postmenopausal women. Considering the accelerated bone mass reduction in menopause, it is necessary to provide other replacements for estrogen which can prevent bone loss. Therefore, because of positive effects of soy protein on bone turnover markers, intake of it in daily diet specially at menopausal women is recommended