Context: Although dietary protein produces higher acute satiety relative to carbohydrate, the influence of protein source and body mass index (BMI) has not been clearly described.

Objective: To assess post prandial responses to different protein sources compared with glucose in males with normal and high BMI.

Design: Randomized cross-over study of four preloads followed by blood sampling (+15, 30, 45, 60, 90, 120, 180min) and buffet meal.

Setting: Outpatient clinic

Participants: 72 men, BMI range 20.6 - 39.9 kg/m²

Interventions: Liquid preloads (1.1MJ; 450ml) containing 50 g of whey, soy, gluten or glucose.

Main Outcome Measures: Fasting and post prandial plasma glucose, insulin, ghrelin, glucagon-like peptide-1 (GLP-1) and cholecystokinin (n = 38), ad libitum energy intake and appetite ratings.

Results: Energy intake was 10% lower after all protein preloads compared with the glucose treatment (P < 0.05), independent of BMI status and protein type. All protein loads prolonged the post prandial suppression of ghrelin (P < 0.01) and elevation of GLP-1 (P < 0.01) and cholecystokinin (P < 0.05). Fasting GLP-1 concentrations (overweight 17.5 ± 1.3; lean 14.7 ± 0.1 pg/mL; (5.2 ± 0.4 and 4.4 ± 0.1pmol/L respectively), P < 0.001) and post prandial responses (P = 0.038) were higher in overweight subjects.

Conclusions: Whey, soy and gluten similarly tend to reduce ad libitum food intake 3 h later in lean and overweight males relative to glucose. Post prandial ghrelin, GLP-1, insulin and cholecystokinin may contribute to this higher satiety after protein consumption. GLP-1 concentrations are increased in overweight subjects which may affect satiety responses in this group.