For example, I went on a trip last week, and ate more than my usual amounts, as well as an additional meal (breakfast).
Now, when I came back, the usual volume of food I ate prior to the trip is not enough to satiate my stomach, as it produces the feeling of hunger a lot earlier than my usual meal times, since I dont eat breakfast.
Clearly my old meals were enough for my body prior to the trip, but now, my stomach “knows” I can eat more if I wanted to, and provides the hunger response.
In: 4
Your stomach stretches to accommodate the amount of food intake you regularly have. There are sensors in the stomach that go off when blood sugar is too low and when you eat too little and leave it too “empty” it causes the stretched stomach to believe it’s not full enough and react accordingly. In a few weeks when you are eating less steadily your stomach will begin to shrink and less food will fill you up.
Stomach doesn’t “know” anything, it’s your brain that receives all sorts of sensory information to make you feel hungry. And it’s not just from the stomach, but also from the blood and from the various organs involved in digestion and water retention (intestines, liver, kidneys, etc.).
Ultimately the cells in your body need not just energy (in the form of glucose sugar levels in your blood), but also vitamins, minerals, water, etc. The stomach can report its contents through the nerve endings attached to it, and through the enzymes and hormones that can be released into the blood stream, but other organs report too.
So yeah, it’s a matter of carbs, fats, proteins, vitamins, water amounts… and also how much effort you’ve been making (energy consumption by the cells in your body), and even expectations (the circadian rhythm, hungry during the day, not so hungry at night when you’re supposed to be sleeping).
Your stomach have multiple different “sensors” which help dictate fullness, volume is just one of them. Your body also tests the stomach contents to see what macro nutrients (carbs, fats, and proteins) are present, which plays a large roll in making you full and keeping you full. Proteins and fats take longer to digest, so they usually contribute to staying full longer. A giant bowl of carbs on the other hand, like a large serving of oatmeal, gets digested very quickly and so you feel hunger again soon.
The amount of fullness you feel is inversely proportional to how long it will take you to feel hungry again; the larger amount of nutrients the more full you’ll feel. This is why we tend not to feel overfill Ed by a salad but a burger and fries makes us feel stuffed.