BACKGROUND: Industrial processing and storage of milk products can strongly increase protein glycation level. Previously, we have reported that ingestion of highly glycated milk protein attenuates the postprandial rise in plasma lysine concentrations compared to the ingestion of an equivalent amount of milk protein with a low glycation level. Whether the attenuated increase in plasma lysine availability is attributed to compromised protein digestion and subsequent lysine absorption remains to be established. OBJECTIVES: The present study combined stable-isotope methodology with the ingestion of specifically produced, intrinsically labeled protein to assess protein digestion and amino acid absorption following ingestion of milk protein with a high versus low glycation level in vivo in humans. METHODS: Fifteen recreationally active, healthy young males participated in this double-blinded, randomized cross-over study. Subjects ingested 40 g intrinsically L-[1- RESULTS: Postprandial plasma lysine concentrations were lower following the ingestion of milk protein with a high versus low glycation level (time × treatment effect: P = 0.002
ƞ CONCLUSIONS: A high level of milk protein glycation strongly reduces postprandial plasma lysine availability in vivo in humans. Industrial processing and storage of (milk) protein products can strongly modulate protein bioavailability and, as such, lower the nutritional value of a protein source. This trial was registered at www. CLINICALTRIALS: gov as NCT05479916.