REVIEW Role of protein and carbohydrate sources on acute appetite responses in lean and overweight men Jane BOWEN, Manny NOAKES and Peter CLIFTON CSIRO Preventative Health Flagship, Obesity Theme, Adelaide BC, South Australia, Australia Abstract 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. Key words: appetite, carbohydrate, ghrelin, GLP-1, overweight, protein. INTRODUCTION Overconsumption of energy from food and beverages is an important precursor 1,2 to the increase in obesity prevalence worldwide. 3–5 The potential role of appetite regulation in managing overweight and obesity warrants investigation, 6 and dietary factors that may modulate appetite are of interest. Dietary patterns with an increased proportion of energy from protein are associated with greater weight loss com- pared with higher carbohydrate intakes. 7–9 Acute studies also show that dietary protein lowers subsequent appetite and energy intake (EI) compared with carbohydrate and fat. 10–13 Little is known about the contribution of gastrointestinal derived appetite hormones (such as ghrelin, a ‘hunger signal’, and satiety signals such as cholecystokinin and glucagon-like peptide-1, GLP-1) to this relationship. Low- glycemic-index carbohydrates are also proposed to extend satiety; 14,15 however, there is substantial disagreement about this relationship 16 and its influence in a mixed diet. Although dietary factors that affect appetite have potential applications in treating overweight and obesity, most appetite studies have been performed in lean subjects. Such findings may not directly translate to the overweight population. 17 This review will summarise the key findings of three previously published studies, 18–20 with an overall objective to investigate the effect of dietary protein and carbohydrate sources on acute changes in gastrointestinal derived appetite hormones, subjective appetite ratings and ad libitum EI in lean and overweight/obese men. These studies were funded by the National Centre of Excellence in Functional Foods. The aims of the three studies were: study 1: to compare the effects of proteins which differ in rate of gastric emptying (whey, fast; casein, slow) with carbohydrates which differ in glycemic index (glucose, high; lactose, low) on appetite responses and rate of gastric emptying over three hours in J. Bowen, BSc, BNutDiet, PhD, Research Dietician M. Noakes, BSc, DipNutDiet, PhD, Senior Research Scientist and Dieti- cian, A/Professor P. Clifton, MBBS, BMedSc, PhD, Obesity Theme Leader, Professor Correspondence: J. Bowen, CSIRO Preventative Health Flagship, Obesity Theme, PO Box 10041, Adelaide BC, SA 5000, Australia. Email: jane.bowen@csiro.au Nutrition & Dietetics 2008; 65 (Suppl. 3): S71–S78 DOI: 10.1111/j.1747-0080.2008.00265.x © 2008 The Authors Journal compilation © 2008 Dietitians Association of Australia S71