system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: why is it that when we get really hungry/haven't eaten in a while food no longer seems apetizing?
gpt
After you've run through the carbs in your bloodstream you revert to 'starvation mode' when your body begins to convert fat into usable energy. In order to make this manageable your brain shuts down the digestive tract and you are no longer 'hungry'.

Right after you run out of carbs you get very, very hungry. A few hours later you aren't hungry anymore because your brain has shut down that part of the body. You will remain not hungry until you eat food (and subsequently run out of blood-stream carbs again) or you run out of fat, in which case you'll get so desperate you'll literally eat babies.

A low-carb diet aims to keep you in fat-burning not-hungry mode until you reach your desired weight, at which point you stop dieting and/or start eating babies.