Background: Although a high-protein diet stimulates the secretion of gastrointestinal (GI) peptides and lowers postprandial glycaemia, the hypothesis that protein-induced satiety is regulated by GI peptides, in particular glucagon-like peptide-1 (GLP-1) and Peptide YY (PYY) remains under debate. This study investigated the dose-response relationship between protein intake, postprandial change in GI peptides, glycaemia and eating behaviour.
Design: 24 overweight women received a 380mL whey protein beverage containing either 0g protein (control; 0 kJ), 12.5g protein (low protein, LP; 210 kJ) or 50.0g protein (high protein, HP; 846 kJ) as a preload breakfast on 3 occasions in a randomised, crossover design. Subjective feelings of appetite were measured using Visual Analogue Scales (VAS) and blood samples were collected over 4 hours post-preload. Subsequently, participants received an outcome lunch meal and were instructed to eat ad libitum (freely) until comfortably full. Energy intake (EI) was recorded.
Results: HP significantly increased postprandial circulating insulin, glucagon and GLP-1, and lowered glycaemia (all, preload * time, p < 0.01). Postprandial PYY was consistently higher after HP when compared to control (preload, p < 0.01), but with no significant increase throughout the postprandial period (preload * time, p > 0.05). HP did not significantly change VAS ratings of hunger, fullness, thoughts of food or satisfaction over 4 hours relative to LP or control (all, preload * time, p > 0.05). Unexpectedly, despite the high protein and energy content of the HP preload, there was no difference in ad lib EI between the 3 beverages (mean ± SEM, control: 3047 ± 314kJ; LP: 2945 ± 225kJ; HP: 2961 ± 259kJ; p > 0.05).
Conclusion: Despite the significant increase in circulating GI peptides following HP beverage, there was no evidence that this in turn resulted in a change in eating behaviour.