Effects of a casein hydrolysate versus intact casein on gastric emptying and amino acid responses

Purpose Milk proteins and/or their hydrolysates have been reported to have beneficial effects for improving postprandial glycaemia. Gastric emptying is a major determinant of postprandial glycaemia, yet limited studies have examined the effects of intact milk proteins compared to hydrolysates on gastric emptying. We investigated gastric emptying of a casein hydrolysate compared to intact casein. Methods Nine overweight and obese adults (mean ± SD age: 59.5 ± 6.5 years and BMI 28.4 ± 2.6 kg/m 2 ) were studied in a randomised crossover design. Gastric emptying was assessed by paracetamol absorption test, with HPLC-MS being used for determining paracetamol and its primary metabolites in plasma. Glucose, insulin and amino acid responses were also assessed. Results Linear mixed model analysis showed no effect of treatment [F (1, 55) = 2.1, P = 0.16] or treatment × time interactions [ F (6, 54) = 1.5, P = 0.21] for paracetamol concentrations. In addition, there were no significant differences between the intact casein and hydrolysate for any of the gastric emptying outcome measures (Cmax, AUC 0–30min , AUC 0–60min ; AUC 0–240min ). However, insulin was increased in the early postprandial period (iAUC 0–15min, iAUC 0–30min; P < 0.05) and there was a treatment effect for glucose [ F (1, 53) = 5.3, P = 0.03] following the casein hydrolysate compared to intact casein. No significant differences in amino acids were found between the two conditions. Conclusions Gastric emptying of a casein hydrolysate compared to intact casein does not differ. Mechanisms other than gastric emptying, for example the presence of a bioactive peptide sequence, may contribute to the glycaemic management effects of certain milk protein hydrolysates and warrant further investigation.