The effect of milk protein fractions on short-term blood glucose control in rats

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Vandenboer, Erik
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Mount Saint Vincent University
The ingestion of whey protein (WP) leads to the reduction of postprandial blood glucose (BG) response paralleled with an increased level of insulin. However, the role of individual WP fractions: glycomacropeptide (GMP), β-Lactoglobulin (β-LG), and α-Lactalbumin (α-LA) remain unclear. The objective of this study was to investigate the effect of WP, GMP, β-LG, and α-LA on BG and insulin response in rats. We hypothesized that due to the difference in their amino acid profile the effect of WP fractions on short-term BG control may differ. Methods: A randomized repeated measures study was conducted in rats fitted with jugular vein catheters and vascular access buttons (VAB). Nine male 10-week-old 275-300g Wistar Han rats were gavaged 350mg (allometrically scaled from a human dosage of 10g) of either intact WP, GMP, β-LG, α-LA, or a glucose control dissolved in 3ml of water after being fasted for 6h during daylight. The use of a VAB allowed for the same rat to receive all five treatments in a random order, with a 48h washout period between treatments. Blood was collected at 0, 15, and 30 min for insulin, and at 0, 15, 30, 60, 90, and 120 min for glucose. Whole blood was analyzed for glucose using a HemoCue 201 Glucose Analyzer, and plasma was analyzed for insulin using a wide range ELISA. The data were tested for normality and analyzed using Two-Way Repeated Measures ANOVA for the effect of time, treatment, and a treatment by time interaction. The data for the area under the curve (AUC) for 2h BG and 30 min insulin were analyzed with One-Way Repeated Measures ANOVA. The differences between the treatments were assessed with Tukey-Kramer post hoc test. Results: There was an effect of treatment (P<0.0001), time (P<0.0001) and a treatment by time interaction (P<0.0001) over 120 min on BG response. Whey protein, GMP, β-LG, and α-LA resulted in significantly lower BG compared to glucose treatment at 15 and 30 min (P<0.05). Blood glucose AUC over 120 min was lower for WP, GMP, and α-LA compared to glucose treatment (P<0.05). There was an effect of treatment (P=0.02), time (P<0.0001) and a treatment by time interaction (P=0.0002) on insulin response over 30 min. Glycomacropeptide had a lower insulin response at 15 min compared to glucose and β-LG (P<0.05). Insulin AUC over 30 min was lower for GMP and α-LA compared to the glucose treatment (P=0.003). Conclusion: At the dose of 350mg WP, GMP, β-LG, and α-LA attenuated BG response at 15 and 30 min, while only WP, GMP, and α-LA attenuated AUC over 120 min compared to the glucose control. GMP attenuated insulin response at 15 min compared to β-LG and the glucose control, and GMP and α-LA attenuated AUC over 30 min compared to the glucose control. This data suggest that WP fractions possess unique properties not observed in WP.
Whey protein , Insulin , Glycomacropeptide , β-Lactoglobulin , α-Lactalbumin , Rats , Nutrition , Blood glucose