Gut mucosal neurons sense fatty acids, sugars, and amino acids, signaling via the vagus nerve to the brain to release dopamine and increase motivation to consume them.

“Diego Bohorquez's lab out of Duke University has done beautiful studies showing that within the mucosal lining of our gut we have neurons that sense fatty acids, sugars, and amino acids, and that when we ingest something that contains one or two or three of those things, there's a signal sent via the vagus nerve up into what's called the nodose ganglion, N-O-D-O-S-E, and then into the brain where it secretes dopamine which makes us want more of that thing, it makes us more motivated to pursue and eat more of that thing, that's either fatty, or umami, savory, or has a sweet taste, any one or two or three of those qualities, independent of the taste.”