Feelings of fullness after eating are believed to be regulated by a sensory system that sends messages from our gut to the appetite-regulating centres in our brain. In our brain, the hypothalamus responds to our nutrient and energy intake, while in the gut, specialised cells produce several different hormones that control our appetite. An understanding about the role these hormones play in appetite control has increased exponentially over the last decade leading to a growing interest among scientists in finding ways to modify these hormones to prevent and treat obesity. The hormones that have intrigued scientists the most have been leptin, ghrelin and cholecystokinin (CKK). However, new gut hormones have been recently identified such as GLP-1, PYY and OXM, all of which appear to play a role in inhibiting food intake and are currently the subject of many research studies. Australian researchers examined the effects of meal composition (varying amounts of fat, protein and carbohydrate) on gastrointestinal hormones, appetite and subsequent energy intakes in a group of lean and obese men. When it came to hormone levels, CCK and ghrelin levels were sustained in response to the high protein and adequate protein meals, but not with the other test meals in both lean and obese men. Overall, this study confirms the satiety-enhancing effects of diets with higher protein content and suggests that gut hormone response may be partially responsible for these effects.