Just thought that a quick trip down physiology lane might help.
You’re having a meal and you put some food into your mouth. Your brain immediately is at work detecting all the elements of the food, such as taste, texture, fats, and sugars that encourage you to keep eating. When you swallow your food and it enters the gastrointestinal tract, your stomach distends and this provides your brain with information about the volume of the food you are eating. At some point in the eating process, signals from your stomach distending and signals emanating from the release of various hormones and neurotransmitters in your stomach and intestines begin to conflict with signals from your mouth. Your brain is getting the message that you’re feeling satisfied (satiated is the fancy term). When your brain gets more and more of these “I’m feeling satisfied” signals, you slow your eating down and then stop.
This is what happens when everything is working right.