The body reads more than intention
Fullness is often treated like a character test. That is too narrow. Appetite is shaped by stomach stretch, food texture, chewing time, digestion speed, hormones, habit, sleep, stress, and what else is happening during the meal.
Fibre enters this picture because it can change the physical experience of food. A meal with pulses, vegetables, whole grains, seeds, or gel-forming fibre may take longer to eat and feel more substantial than a low-structure snack. This is not a weight-loss promise. It is a material observation. The body responds differently to food that has body, water, chew, and time built into it.