By Zheng Y, Lee S-O, Verbruggen MA, Murphy PA, Hendrich S. Apparent absorption of isoflavone glucosides and aglycones is similar in women and increased with rapid gut transit time and low fecal isoflavone degradation. Am. Society for Nutr. Sc. 5 (2004): 2534-2539.
Bioavailability” indicates to what extent active compounds are absorbed. In the case of isoflavones: glycosides are absorbed through the gut wall after substantial bacterial metabolism