Larry Krug, chief executive officer of Eatwize.com, an online nutrition consultancy, says: This condition is called 'sensory-specific satiety'. It's perfectly normal and occurs on two levels: psychological and physiological. Firstly there's pure habit. At a young age people are rewarded with sweets and desserts for eating a healthy meal. We come to anticipate and expect it after experiencing that feeling of satiety from eating a full meal. It's an emotional, psychological response, but if you wait long enough after eating, these feelings will most likely subside.
Physiologically, a meal high in carbohydrates but low in fat may leave you feeling full but not satiated because you have not satisfied all aspects of your appetite. Since you're full, you'll be inclined to eat no more of the foods that made you full, but you may still crave other taste sensations such as desserts, which are usually high in fat. When you eat fat, the hormone cholecystokinin is released in your stomach and this sends a message to your pituitary gland to sense satisfaction. The desire for dessert is just your body's ancient response to the need to stay well stocked with fats.