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: The objective of the study was to assess postprandial responses to different protein sources, compared with glucose, in males with normal and high BMI.
Design: This was a randomized, crossover study of four preloads followed by blood sampling (+15, 30, 45, 60, 90, 120, 180 min) and buffet meal.
Setting: The study was conducted at an outpatient clinic.
Participants: The study population included 72 men, with a BMI range 20.6-39.9 kg/m(2).
Interventions: Interventions consisted of liquid preloads (1.1 MJ, 450 ml) containing 50 g whey, soy, gluten, or glucose.
Main outcome measures: Fasting and postprandial plasma glucose, insulin, ghrelin, glucagon-like peptide-1 (GLP-1) and cholecystokinin (n = 38), ad libitum energy intake, and appetite ratings were measured.
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 postprandial 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 +/- 0.1 pmol/liter, respectively); P < 0.001] and postprandial 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. Postprandial 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.