Isoflavones

• Phytoestrogens have been considered to be weakly estrogenic and serum levels of isoflavones and their metabolites can reach the low micromolar level (about 100– 1000 times that of estradiol)

• Therefore, even with a weak potency, isoflavones could potentially exert biological effects in vivo.

• Isoflavones have attracted attention mainly due to their role in the amelioration of postmenopausal symptoms such as hot flushes and osteoporosis

• Many epidemiological studies, clinical and dietary intervention trials have evaluated the effects of isoflavones on menopausal symptoms, cardiovascular function, and endocrine regulation of the menstrual cycle

• Overall, results are strongly contradictory. Some studies show positive effects such as the reduction of hot flushes, the excretion of bone resorption biomarkers and the increase in bone mineral density while other studies report the lack of effects

• Various meta-analyses have also been published reporting either the lack or doubtful effects ([Gardner et al., 2001] and [Weggemans and Trautwein, 2003]), very low or modest effects (Trock et al., 2006) or clear positive effects (Reynolds et al., 2006) of isoflavones.

• The possible adverse effects derived from isoflavone consumption are also a matter of debate. Some studies have reported the induction of alterations of the reproductive development in female mice (Takashima-Sasaki et al., 2006), in pregnant and lactating rats, as well as in suckling pups consuming high doses of isoflavones (1 g/kg) (Ikegami et al., 2006)

• Some clinical studies suggested that soy phytoestrogens stimulate epithelial cell proliferation in breasts of pre-menopausal women (McMichael-Phillips et al., 1998). •Due to the possible adverse effects of isoflavones and the lack of consensus regarding the health benefits derived from isoflavones consumption, The American Heart Association does not recommend the use of isoflavone supplements in food or pills

Effect of the soy isoflavone genistein on bone health

• Copyright ©2005 American Society for Nutrition Weaver, C. M. et al. J. Nutr. 2005;135:1243-1247 Effect of the soy isoflavone genistein on bone health

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Mean ({+/-}SE) bone mineral density (BMD) of the lumbar spine in the isoflavone-treatment (IF+) and control (IF-) groups

• Mean (±SE) bone mineral density (BMD) of the lumbar spine in the isoflavone-treatment (IF+) and control (IF–) groups

• Data for 118 IF+ subjects (white) and 119 IF– subjects (black)

• Brink, E. et al. Am J Clin Nutr 2008;87:761-770

Isoflavones, estrogen, and life cycle

• Female hormone levels and isoflavone intake during various life stages

  
  

• Abbreviations: IF = isoflavones, bwt = body weight

  
  

• The line represents estradiol levels (left axis values) and the shaded area represents the approximate range of IF consumption (right axis values) for

• (A) infants fed soy-based formula,

• (B) adults consuming a soy-rich diet, and

• (C) menopausal women consuming a soy-rich diet in addition to soy supplements