The image of a stoner always having the munchies is a stereotype because it's true - and it's true, say researchers, because it has a basis in biology.

Daniele Piomelli, Nicholas DiPatrizio and colleagues found that fats in foods like potato chips and french fries trigger a biological mechanism - and that is driven by natural marijuana-like chemicals in the body called endocannabinoids.

In their study, they discovered that when rats tasted something fatty, cells in their upper gut started producing endocannabinoids but sugars and proteins did not have this effect.

The process starts on the tongue, where fats in food generate a signal that travels first to the brain and then through a nerve bundle called the vagus to the intestines. There, the signal stimulates the production of endocannabinoids, which initiates a surge in cell signaling that prompts the wanton intake of fatty foods, probably by initiating the release of digestive chemicals linked to hunger and satiety that compel us to eat more.

“This is the first demonstration that endocannabinoid signaling in the gut plays an important role in regulating fat intake,” said Piomelli, the Louise Turner Arnold Chair in the Neurosciences and professor of pharmacology.

From an evolutionary standpoint, there’s a compelling need for animals to consume fats, which are scarce in nature but crucial for proper cell functioning. In contemporary human society, however, fats are readily available, and the innate drive to eat fatty foods leads to obesity, diabetes and cancer.

The findings suggest it might be possible to curb this tendency by obstructing endocannabinoid activity – for example, by using drugs that “clog” cannabinoid receptors. Since these drugs wouldn’t need to enter the brain, they shouldn’t cause the central side effects — anxiety and depression — seen when endocannabinoid signaling is blocked in the brain.

Giuseppe Astarita of UCI and Gary Schwartz and Xiaosong Li of New York’s Yeshiva University contributed to the study, which received support from the National Institute of Diabetes&Digestive & Kidney Diseases and the National Institute on Drug Abuse.

Study results appear this week in the online edition of Proceedings of the National Academy of Sciences.