Gastric digestion and changes in serum amino acid concentrations after consumption of casein from cow and goat milk: a randomized crossover trial in healthy men

In vitro studies show that goat milk proteins form less compact coagulates in the stomach compared to cow milk proteins, which may facilitate gastric digestion and amino acid (AA) absorption. However, this has not been confirmed in vivo in humans. To examine gastric digestion and changes in serum AA concentrations after cow milk-derived (cow MC) and goat milk-derived casein (goat MC) ingestion. In this single-blind randomized cross-over study participants consumed 300 ml of a drink containing 30 g of cow MC or goat MC. Participants underwent gastric MRI scans at baseline and every 10 minutes up to 60 minutes postprandially. Blood was drawn at baseline and up to 4 hours 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. 18 men (age 26 ± 8.3 years, BMI 23 ± 1.6 kg/m2) completed the study. Gastric emptying half-time was 80 ± 25 minutes for goat and 85 ± 24 minutes for cow MC (p = 0.395). In line with this, gastric emptying of the drinks over time was similar (MD 0.77 ml, 95% 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). 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. NL8137 (Netherlands Trial Registry), accessible through https://trialsearch.who.int/Trial2.aspx?TrialID=NL-OMON28580.