Use of Isotope-Labeled Body or Dietary Proteins to Determine Dietary Amino Acid Digestibility

Amino acid (AA) digestibility in humans has been determined conventionally based on oro-ileal AA disappearance. With this approach, it is necessary to account for undigested AAs of body origin (endogenous AAs) found in the ileal digesta. Determination of the endogenous AAs under physiological conditions is not straightforward, and the use of isotopes (labeled foods or body tissues) has been pivotal to advancing our understanding. The application of isotopes for determining gut endogenous AAs and AA digestibility is discussed as well as the types of digestibility coefficient generated (apparent, true, real) dependent upon methodology. Recently a new dual isotope-based method for determining ileal AA digestibility in humans has been developed that obviates the collection of ileal digesta. The dual isotope method, which awaits full validation, offers considerable promise for making noninvasive measures of AA digestibility in humans of different ages and physiological states.

Automated summary

The traditional method for determining amino acid (AA) digestibility in humans is based on oro-ileal AA disappearance. It is necessary to consider the undigested AAs of body origin (endogenous AAs) found in the ileal digesta. The use of isotopes has been crucial in advancing our understanding of the determination of endogenous AAs and AA digestibility. A new dual isotope-based method for determining ileal AA digestibility in humans has been developed, which has the potential to provide noninvasive measures of AA digestibility in humans of different ages and physiological states.