Abstract
We investigated the bioavailability of soy isoflavones from processed soybean products. Five healthy male volunteers ingested soy milk, soy curd (tofu) , boiled soybeans (nimame) , or fermented soybeans (natto) in a single dose, and blood was collected 90 min later for measurement of the plasma isoflavone concentration. Each subject ingested test meals containing an isoflavone equivalent of 50 mg aglycone. The total amount of each isoflavone was determined by HPLC analysis after deconjugation of conjugated metabolites using sulfatase H-1. The concentration of glycitein was below the detection limit before and after intake of the soybean products. The concentrations of daidzein and genistein were elevated in all subjects after ingestion of all the test meals, and the concentration of genistein was higher than that of daidzein except after ingestion of fermented soybeans. Ingestion of boiled soybeans appeared to result in a higher concentration of total isoflavones (daizein and genistein) than ingestion of soy curd. These results suggest that the bioavailability of isoflavones from soybeans varies according to the type of processing.
