Acute effects of oral microbial protease co-ingestion with whey protein on postprandial plasma amino acid concentrations, appetite, and satiety in healthy adults: a randomized, double-blind, placebo-controlled, crossover clinical trial.

Background: Proteases are enzymes that break down proteins into peptides and amino acids. When co-ingested with dietary protein, proteases may enhance digestion, increase postprandial plasma amino acid concentration, and affect gut hormones, appetite, and/or satiety.

Objectives: The aim of this study was to assess the effects of a mixture of 3 microbial protease preparations (P3) on postprandial plasma amino acid concentration when co-ingested with whey protein concentrate (WPC) in healthy young adults.

Methods: P3 was first tested in vitro for proteolytic effects in a static simulation of oro-gastric digestion. In a subsequent randomized, double-blinded, placebo-controlled crossover study, 12 males and 12 females (BMI: 23.6 (2.9) kg·m^-2; age: 25 (3) years [mean (SD)]) consumed WPC (25g protein) containing P3 or placebo (maltodextrin). Plasma amino acid, glucose, insulin, and appetite regulatory hormone concentrations were assessed at baseline and throughout a 240-min postprandial period. Perceived appetite sensations were assessed by visual analog scale (VAS) questionnaires. An ad libitum meal was administered following each treatment to determine energy intake.

Results: P3 demonstrated proteolytic activity at 50,000 HUT per 31.9g serving of WPC in vitro. Adjusted geometric mean postprandial plasma 60-min incremental area-under-the-curve (iAUC) was 14% greater for essential amino acids (EAA) (Treatment: P=0.025), and 15% greater for branched-chain amino acids (BCAA) (Treatment: P=0.021) with P3 versus placebo, with no differences for total amino acids or leucine (all P>0.05). Adjusted geometric mean postprandial plasma ghrelin was 11% lower (Treatment: P<0.001), while adjusted mean VAS-derived fullness (Treatment: P=0.025) and satiation (Interaction: t=30-150 min; all P<0.05) were greater with P3 versus placebo. Adjusted mean postprandial plasma glucose, insulin, and ad libitum meal energy intake were not different between treatments (all P>0.05).

Conclusion: Co-ingestion of WPC with P3 can enhance early postprandial plasma aminoacidemia and alter select indices of appetite and satiety in young adults.

Clinical trial registry: This trial was prospectively registered at ClinicalTrials.gov (NCT05957185).