Receptors in the gut sense amino acids and sugars, signaling to the brain about how much more of a food to consume.

“what I'm understanding based on what you're telling me is that all along the pathway from our mouth to our rectum we have sensory cells that are evaluating the chemical constituents of the foods that we eat emitting broad kind of maybe even crude slow signals in the form of hormones to change our appetite our feelings of well-being maybe our feelings of not wellbeing um but also sending direct signals to the brain to drive certain types of thinking emotions and behavior”