In a land far far away there lived two goblins called Gherlin and Leptin. The two were inseparable. Ok, I am just trying to make sure you are awake while you read this. There is no land far away and leptin and gherlin are not goblins. Instead they are the two hormones that regulate your hunger and satiety. The first, Gherlin, plays the role of initiating the felt need to consume the good stuff. The second, Leptin, tells you (hopefully?) when you have had enough and its time to end the feasting.
Gherlin a.k.a. the hunger hormone gets activated when the stomach is empty. Activation prompts the secretion of gastric acids in the stomach to prepare the stomach for the bread and cake that you will partake. Once you have had your fill and your stomach is stretched to the brim, gherlin stops secreting. Interestingly, gherlin can cross the blood-brain barrier and is also linked to the reward receptors in your brain which provides you pleasure. This is the reason you feel good after a meal.
Leptin on the other hand is a.k.a the satiety hormone. It is this that tells you enough is enough and you are not really built to consume a two pounder. In a strange twist of fate, if your body carries high body fat it inhibits the functioning of leptin. This creates a resistance or insensitivity to leptin. As a result, your body does not understand that you are satiated making you eat more. Various reason are ascribed for this resistance. It is believed that the extra triglycerides in your body inhibit its functioning. Also, it is believed that your body creates leptin resistance much like it does insulin resistance in those who have Type 2 diabetes.
Together, the dance of the goblins is called energy homeostasis. It is this dance that keeps you alive.