A meal changes signaling in the gut first. But the effect does not stay there. Information about stretch, nutrients, and hormones moves up the routes that connect the gut to the brain, and different regions do different things with it.
Four regions stand out. The hypothalamus reads the meal for energy balance and adjusts hunger. The brainstem reads it for internal state, which is where fullness, and sometimes nausea, gets registered. The reward areas read it for value, which is why some foods feel worth more than others. The prefrontal cortex and amygdala read it for what to do next, the difference between a deliberate choice and a reactive one.
This is why the gut-brain frame matters. Food is not just broken down. It is turned into signals that several parts of the nervous system read at once, each for its own job.
The point is coordination. One meal can move several systems at once because the signal is read in several places at once.