The effect of milk proteins co-ingested with glucose on blood glucose control in rats
Mount Saint Vincent University
The ingestion of whey protein (WP) leads to the reduction of postprandial blood glucose (BG) response paralleled with an increased insulin response. However, the role of glycomacropeptide (GMP), βlactoglobulin (β-LG),α-lactalbumin (α-LA), micellar casein (MC), and total milk protein (TMP) remains unclear when these proteins are consumed with a glycemic carbohydrate. The objective of this study was to investigate the effect of co-ingestion of WP, GMP, β-LG, α-LA, MC and TMP with glucose on BG and insulin response in rats. We hypothesized that milk protein fractions co-ingested with glucose will reduce blood glucose response and increase insulin response compared to glucose ingested alone. Methods: A randomized repeated measures study was conducted in rats fitted with jugular vein catheters and vascular access buttons (VAB). Ten male 10-week-old 275-300g Wistar Han rats were gavaged 350mg (allometrically scaled from a human dosage of 10g) of WP, GMP, β-LG, α-LA, MC, TMP co-ingested with glucose 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 seven 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 time (P<0.0001), a treatment by time interaction (P<0.0001) but no effect of treatment (P=0.35) over 120 min on BG response. There was an effect of time (P<0.0001), a treatment by time interaction (P<0.0001) and an effect of treatment (P=0.03) on BG response over 30 min. WP, GMP, β-LG, α-LA, TMP and MC resulted in a lower BG compared to glucose treatment at 15 and 30 min (P<0.05). Blood glucose AUC over 30 min was suppressed after WP treatment compared to glucose alone (P<0.05). There was an effect of time (P<0.0001) and a treatment by time interaction (P=0.0002) but no effect of treatment (P>0.05) on insulin response over 30 min. There was no effect of a treatment on insulin AUC over 30 min (P=0.4). Results: at the dose of 350mg WP, GMP, βLG, α-LA, MC and TMP co-ingested with glucose attenuated BG response at 15 and 30 min, and WP coingested with glucose attenuated BG response over 30 min compared to glucose alone. The co-ingestion of milk protein fractions with glucose resulted in an elevated insulin response similar to the insulin response when glucose was ingested alone.