Author
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ZUBIK, LIGIA - HNRCA |
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MEYDANI, MOHSEN - HNRCA |
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Submitted to: The American Journal of Clinical Nutrition
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 10/24/2002 Publication Date: 6/1/2003 Citation: Zubik, L., Meydani, M. 2003. Bioavailability of soybean isoflavones from aglycone and glucoside forms in american women. American Journal Of Clinical Nutrition 2003;77:1459-65. Interpretive Summary: Isoflavones, the functional compounds found in soybeans, are thought to play a role in preventing cancer, osteoporosis, postmenopausal syndromes, and high cholesterol. Glucoside and aglycone forms are the two main chemical structures of isoflavones found in soybean foods. Daidzin and genistin are the common glucoside forms found in soybeans, while daidzien and genistein are the common aglycone forms. Following ingestion, the glucoside form is broken down into the aglycone form, which is either directly absorbed, or may be metabolized by intestinal bacteria into further compounds such as equol. Based on animal studies, no difference in the absorption rates has been observed for consumption of both isoflavone forms. However, human studies are unclear. The purpose of this study is to investigate the time the common soy isoflavones take to travel through the body, be absorbed and utilized, as well as their availability after consumption of both glucoside and aglycone isoflavone forms by American women. We have found that the major isoflavones present in soybean and soybean products when ingested in either the glucoside or aglycone form by American women have no significant difference in absorption or availability. Understanding the route that isoflavones take in the human body allows for further investigation into determining which specific soy isoflavones may potentially prevent disease and improve health and the mechanism through which they individually perform. Technical Abstract: Even though the bioavailability of isoflavones from aglycone forms is believed to be higher than glycosides, human studies testing the bioavailability of isoflavones in Eastern and Western human subjects have been contradictory. To investigate the postprandial absorption and bioavailability of soy isoflavones, daidzein, and genistein in American women with typical American dietary habits following the ingestion of aglycone or glucoside forms of isoflavones. 15 American women ages 46 +/- 6 y with typical American dietary habits participated in a randomized, double blind study. Subjects¿ blood samples were collected before and after 1, 2, 4, 8, 12, 24, and 48 h after consumption of isoflavone aglycone or glucoside tablets with breakfast. The plasma appearance and disappearance curves for daidzein, genistein, and equol (a metabolite of daidzein) were constructed and the postprandial maximum concentration in plasma (Cmax) and time to reach to the maximum concentration (tmax) as well as area under the curve (AUC) as an apparent bioavailability were determined over a 48 h post-ingestion period. There was an early rise (1-2 h) of isoflavones in plasma followed by a slight decline and then a second peak at 4-8 h. There was no difference in mean plasma Cmax, or tmax or AUC for genistein following ingestion of aglycone or glucoside forms. However, Cmax and AUC, but not tmax were significantly higher for daidzein when aglycone was consumed, which was in part due to the presence of a relatively higher content of daidzein in the aglycone tablets. Equol in plasma appeared after 4 h and remained elevated after 48 h. Despite a higher content of daidzein in aglycone tablets, the AUC of equol was higher following the ingestion of glucoside tablets probably due to longer intestinal transient time of glucoside and production of bacterial metabolites in the intestine. The bioavailability of genistein and daidzein, the major isoflavones present in soybean and soybean products, is not different when consumed as either aglycone or glucoside by American women. |
