Hunger and cravings are two different sensations. The body regulates the former, while the mind wields greater power over the latter. Hunger serves a more utilitarian purpose, signaling our brains that it's time to eat. To cross that distance between the stomach and brain, the vagus nerve is the communication highway that runs between the noggin and the abdomen.
Our stomach hunger cycle, in a nutshell, begins with a hormone called ghrelin. When our bodies have burned up the food in our stomachs and our blood sugar and insulin levels begin to drop, ghrelin communicates with the hypothalamus in the brain. The hypothalamus, housed in the deep center portion of our brain cavity, regulates our basic body functions such as thirst, sleep and sex drive. Once it receives the message, delivered by ghrelin, that we need to eat something to keep our bodies running, the hypothalamus triggers the release of neuropeptide Y, which stimulates our appetites [source: Wright].
When we recognize that our body wants food and we start to refill it, another process happens to counter that hunger feeling in order to keep us from gorging ourselves. First, the fat tissues expel the hormone leptin. This chemical tells our brains that our bodies are satisfied and we can stop eating. It does so by turning down the production of neuropeptide Y and cranking up levels of proopiomelanocortin, an appetite suppressant, in our bloodstream [source: Wright]. The hypothalamus also monitors our insulin and blood sugar levels to ensure that we've eaten enough to bring those levels back up. Since this process doesn't happen instantaneously, we may feel uncomfortably stuffed after finishing a large meal.
Now that we know how our body responds to the absence of food, what happens when mind takes over matter? If ghrelin isn't telling me that I want a deluxe cheeseburger, what is? Things get a little more complicated when food desires move from the stomach to the brain.