Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Theses & dissertations (Interdisciplinary)



First Advisor

Suzanne Hendrick


Lower incidence of breast cancer in Asia has been connected to the higher intake of isoflavone containing soy foods. The effort in study of soy isoflavones as health protective compounds has come to some positive results, like their effects in cancer prevention, lowering blood cholesterol level and osteoporosis prevention. In order to characterize the bioavailability of the third major isoflavone glycitein and to assess its potential health protective effects, a comparison study with other isoflavones was conducted in humans with moderate fecal isoflavone degradation activity. The average 48 h urinary excretions of daidzein, glycitein and genistein were 50, 45 and 35% of total dose ingested, respectively, at which daidzein and glycitein were not different from each other but they were significantly greater than genistein (p = 0.01). Plasma isoflavone concentrations paralleled relative amounts of isoflavones in soymilk at 6 and 24 h but not in soygerm in women at 6 h;To characterize soy isoflavone metabolism, three feeding protocols were conducted in women. By using selective hydrolysis enzymes, the distribution of glucuronide and aglycone isoflavones in both urine and plasma were obtained. At 3 h after soymilk intake, 59.4% of daidzein and 50.9% of genistein over total appeared in plasma as glucuronides. About 76.8% of total daidzein and 70.9% of total genistein present in urine (24 h) were glucuronides. Significantly higher percentages of aglycone appeared in plasma than in urine. A steady state was observed with six consecutive days feeding. As the major metabolite of isoflavone, the glucuronide forms might contribute to observed effects of soy isoflavones;The major metabolites of daidzein and genistein glucuronides were assayed for their ability to modulate human natural killer (NK) cells and NK3.3 cell line alone or in combination with aglycone daidzein and genistein in nutritionally relevant concentrations. Daidzein and genistein glucuronides were as active as their aglycone counterparts but activated human NK cells in a wider range (up to 10 mumol/L) than aglycone isoflavones (below 5 mumol/L). No activation was observed with NK3.3 cell line for both daidzein and genistein. These data suggested that soy isoflavone metabolites indirectly activated human NK cells.



Digital Repository @ Iowa State University,

Copyright Owner

Yan Zhang



Proquest ID


File Format


File Size

140 pages