Why does your hunger go away if you don't eat?

Activity increases after the stomach and small intestines have been empty for approximately two hours. Receptors in the walls of the stomach sense the absence of food, causing a reflex generation of waves of electrical activity (migrating myoelectric complexes, or MMCs) in the centric nervous system. These MMCs travel along the stomach and small intestines and lead to hunger contractions. Such hunger contractions start in the antrum, or lower region, of the stomach and propagate along the entire length of the gut, sweeping to the terminal ileum. They clear out any and all stomach contents including mucus, remaining foodstuffs and bacteria and keep them from accumulating at any one site.

The contractions also produce vibrations and the rumbling noise associated with hunger. Hunger contractions may continue for 10 to 20 minutes once initiated, and then repeat every one to two hours until the next meal is ingested. These are not the same as hunger pangs, which start 12 to 24 hours after the last meal and may continue for a few days before gradually subsiding. (It is possible such pangs are important in the hunger sensation that drives animals to eat.) Low blood sugar enhances this activity, which can also be induced using an intravenous infusion of the hormone motilin. After feeding, the MMCs subside. http://www.sciam.com/health/article/id/why-does-your-stomach-gro

xox Sika