Role of protein and carbohydrate sources on acute appetite responses in lean and overweight men

Dietary protein induces greater satiety compared with carbohydrate in lean subjects, which may involve appetite-regulatory gut hormones. Little is known about the duration of effect, influence of protein and carbohydrate source and relevance to non-lean individuals. We compared the effect of various dietary proteins and carbohydrates on post-prandial appetite ratings, ad libitum energy intake (EI) and appetite hormones in lean and overweight men. Three randomised double-blinded cross-over studies examined appetite response (appetite ratings, ghrelin, glucagon-like peptide-1 (GLP-1) and cholecystokinin) to liquid preloads over three to four hours followed by a buffet meal to assess ad libitum EI. The 1-MJ preloads contained ∼55 g of protein (whey, casein, soy and gluten), carbohydrate (glucose, lactose and fructose) or combined whey/fructose. EI was 10% higher following glucose preloads compared with protein preloads, observed at three hours but not four hours. Protein ingestion was followed by prolonged elevation of cholecystokinin and GLP-1 (two hours) and suppression of ghrelin (three to four hours) compared with glucose and independent of protein type. Replacing some whey with fructose attenuated the effect of protein on these hormones. Treatment effects on EI and appetite hormones were independent of bodyweight status, despite higher GLP-1 and lower ghrelin in overweight subjects. Protein-rich liquid preloads reduce EI over three hours in overweight men compared with glucose. These findings suggest a potential application for protein-rich drinks and/or foods to facilitate reduced EI. Future studies should explore additional dietary manipulations that may enhance this relationship, and confirm these effects within the context of energy-restricted dietary patterns.