Can someone explain in simple terms how recovery of polyphenols in urine informs bioavailability of that compound?
Oral or dietary polyphenols that appear in the Urine, after ADME (absorption, distribution, metabolism and excretion) are assumed to be bioavailable (BV). In a agreement with Professor Shi, metabolims of polyphenols could lead to "underestimation" of the bioavailability. So "urinary bioavialablity" is the lower estimate whist the actual could be grater? In principle, to improve the accuracy of BV determinations the excreted (Urinary) value should combine the net concentration of all metabolites and non-metabolized polyphenols (not easy to measure).
Alternative measures of bioavailabilty exist as you know.
Pharmacolgists define BV as; = Area under curve -with oral route/ Area under curve IV route.
Nutrition scientists consider "digestbility" or Retention as more relevant or practical. Nutrient digestbility = 100*(Intake - (Feceal + Urinary)/ Intake.
I have not thought much about this but, I think the general concensus is that all current definitions and measures of BV have some limitations (?). It would be interesting to see what others think.
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