The Incorporation of Dietary Protein-Derived Amino Acids in Duodenal Mucosal Protein in Young and Older Males

Rationale: Aging is accompanied by a blunted muscle protein synthetic response to protein ingestion.This anabolic resistance may be related to decreased postprandial amino acid release in the circulation, due to greater amino acid extraction by splanchnic tissues in older individuals. It has been suggested that extracted amino acids are utilized by intestinal epithelial cells for cell proliferation, generating new cells to maintain healthy mucosa. So far, there is no evidence that dietary protein-derived amino acids are taken up and incorporated in intestinal mucosal protein in vivo in humans. Furthermore, there is no evidence that this process is impacted by age. Objective: To assess the postprandial incorporation of dietary protein-derived amino acids in intestinal mucosal protein in healthy young and older males. Study design: Cross-sectional, non-therapeutic intervention study design Study population: 5 healthy, non-obese (BMI 18.5-30kg/m2) young adult males (age: 18-35y inclusive) and 5 community dwelling older males (age: 67+y). Intervention: Continuous intravenous stable isotope amino acid tracer infusion will be applied, in combination with oral ingestion of 20g intrinsically labelled milk protein, with plasma, muscle and duodenal mucosa biopsy samples collected at different time points throughout the experimental test day. Main study parameters/endpoints: The primary study outcome is the postprandial (0-5h) incorporation of dietary protein-derived amino acids in duodenal mucosal protein following the ingestion of 20g intrinsically labelled milk protein. Secondary study parameters include postprandial plasma availability of dietary protein-derived amino acids and fractional duodenal mucosal protein synthetic rate.