Soy Isoflavone Bioavailability and Pharmacokinetics
Not all soy foods or supplements contain the same amount or percentage of the three primary isoflavones genistein, daidzein or glycetein. Soyfoods and supplements can vary in soy isoflavone amounts and forms which, in turn, may impact the way the body will metabolize the isoflavones and subsequently can impact their effectiveness in health care, the report states.
For example, the rates of absorption in the body of the isoflavones daidzein and genistein depend on their form. As glycosides, which have an attached sugar molecule, both isoflavones can reach a peak plasma concentration in four to 10 hours. However, the human body cannot use this form, and during digestion the sugar is removed. This resulting aglycone form can be absorbed faster. When consumed as aglycosides, both daidzein and genistein can achieve peak concentrations in just one hour, or up to three hours if eaten with a meal. When the daidzein metabolite S-equol is consumed, its peak plasma rate rapidly occurs in just one to two hours.
The time needed for the total plasma concentration of either isoflavone to decrease by half typically is six to 12 hours and for S-equol, six to eight hours. However, genistein takes significantly longer to leave the body than daidzein. S-equol is excreted almost exclusively in urine, with 75 percent excreted within 12 hours after consumption.
Soy-isoflavones Reasonable for Menopausal Symptoms
The NAMS report advises that in postmenopausal women with distressing vasomotor symptoms, such as hot flashes, initial treatment with soy isoflavones is reasonable because of demonstrated modest effectiveness in early post-menopausal women who have at least four hot flashes daily. The report recommends a starting dose of 50 milligrams (mg) or more daily for at least 12 weeks. If a woman responds, the treatment can continue with monitoring for side effects
|Contact: Stephen McCauley|