According to The Wall Street Journal's Health Journal, scientists have determined that food cravings are not a result of the "nutrional-deficiency notion" -- an attempt by the body's subconscious to request things it needs -- but a "complex mix of social, cultural and psychological factors, heavily influenced by environmental cues."

Functional MRI scans by Dr. Pelchat showed that sensory memory food cravings activate the same parts of the brain that drug and alcohol cravings do, including the hippocampus, which helps store memories; the insula, involved in perception and emotion; and the caudate, which is important for learning and memory. The circuit is driven by dopamine, the neurotransmitter responsible for reward-driven learning.

Experts say that cravings are fine on occasion -- say, for pumpkin pie at Thanksgiving, gingerbread at Christmas or for healthy choices year-round. But indulging too often can send cravings spiraling out of control.

Brain researchers have documented that when people continually bombard their reward circuits with drugs, alcohol or high-fat, high-sugar foods, many of the dopamine receptors in the system shut down to prevent overload. And with fewer dopamine receptors at work, the system craves more and more, insatiably. "Pretty soon, one cupcake doesn't do it anymore. You have to overstuff yourself and you still don't get that reward," says Pam Peeke, a physician and author of the new book, "The Hunger Fix." She notes that food addiction creates changes in the prefrontal cortex, which normally override impulsivity and addictive urges.