Gastric Digestion and Changes in Serum Amino Acid Concentrations after Consumption of Casein from Cow and Goat Milk: A Randomized Crossover Trial in Healthy Males

Background: In vitro studies show that goat milk proteins form less compact coagulates in the stomach compared with cow milk proteins, which may facilitate gastric digestion and amino acid (AA) absorption. However, this has not been confirmed in vivo in humans. Objectives: This study aims to examine gastric digestion and changes in serum AA concentrations after cow milk-derived (cow MC) and goat milk-derived casein (goat MC) ingestion. Methods: In this single-blind randomized crossover study participants consumed 300 mL of a drink containing 30 g of cow MC or goat MC. Participants underwent gastric magnetic resonance imaging (MRI) scans at baseline and every 10 min ≤60 min postprandially. Blood was drawn at baseline and ≤4 h postprandially. In addition, participants verbally rated their appetite after each MRI measurement. Primary outcomes were gastric emptying and serum AA concentrations. Secondary outcome was gastric coagulation as inferred by image texture metrics. Results: A total of 18 males (age 26 ± 8.3 y, body mass index 23 ± 1.6 kg/m²) completed the study. Gastric emptying half-time was 80 ± 25 min for goat and 85 ± 24 min for cow MC (P = 0.395). In line with this, gastric emptying of the drinks over time was similar [mean difference (MD) 0.77 mL; 95% confidence interval (CI): −6.9, 8.5; P = 0.845]. Serum essential AA (MD −110 μmol/L; 95% CI: −162, −58) was higher over time for cow MC (P < 0.001). The image texture metric contrast was lower for cow MC (MD 0.010; 95% CI: 0.001, 0.020; P = 0.036). Conclusions: Cow and goat MC have different coagulating properties, as inferred by AA concentrations and supported by image texture analysis. However, overall gastric emptying and the emptying of the liquid and coagulated fractions were similar. This warrants further in vivo research on casein coagulation in the food matrix to help determine the optimal use for cow and goat milk and their protein fractions.