Mechanism of Action of Pre-meal Consumption of Whey Protein on Glycemic Control in Young Adults

Whey protein (WP), when consumed in small amounts prior to a meal, improves post-meal glycemic control more than can be explained by insulin-dependent mechanisms alone. The objective of the study was to identify the mechanism of action of WP beyond insulin on the reduction of post-meal glycemia. In a randomized crossover study, healthy young men received preloads (300 ml) of WP (10 and 20 g), glucose (10 and 20 g) or water (control). Paracetamol (1.5 g) was added to the preloads to measure gastric emptying. Plasma concentrations of paracetamol, glucose, and β-cell and gastrointestinal hormones were measured before preloads (baseline) and at intervals before (0-30 min) and after (50-230 min) a preset pizza meal (12 kcal/kg). Whey protein slowed pre-meal gastric emptying rate compared to the control and 10 g glucose (P<.0001), and induced lower pre-meal insulin and C-peptide than the glucose preloads (P<.0001). Glucose, but not WP, increased pre-meal plasma glucose concentrations (P<.0001). Both WP and glucose reduced post-meal glycemia (P=.0006) and resulted in similar CCK, amylin, ghrelin and GIP responses (P<.05). However, compared with glucose, WP resulted in higher post-meal GLP-1 and peptide tyrosine-tyrosine (PYY) and lower insulin concentrations, without altering insulin secretion and extraction rates. For the total duration of this study (0-230 min), WP resulted in lower mean plasma glucose, insulin and C-peptide, but higher GLP-1 and PYY concentrations than the glucose preloads. In conclusion, pre-meal consumption of WP lowers post-meal glycemia by both insulin-dependent and insulin-independent mechanisms.