Satiety
The feeling of fullness that ends a meal and keeps hunger away afterwards.
Satiety is how full you stay after eating. Nutrition science separates it from satiation, which is what makes you stop mid meal; satiety is the part that decides whether you are hunting for biscuits two hours later.
It runs on signals rather than willpower. Stomach stretch reports volume, gut hormones including GLP-1, PYY and cholecystokinin report what has arrived and slow the stomach's emptying, and leptin from fat tissue reports longer term energy stores to the brain. Understanding it as physiology rather than character changes how you design a diet.
Some foods are dramatically more satiating than others per calorie, and the pattern is consistent: protein leads, then fibre, then volume and water content, with texture playing a real part because food that takes longer to eat delivers its signals before the meal is over.
This is the mechanism behind the ultra processed food finding. In a metabolic ward trial where meals were matched for calories presented, sugar, fat, sodium and fibre, people freely eating an ultra processed menu took in about 508 kcal a day more and gained weight, then lost it on the unprocessed arm. Softer, faster, more energy dense food defeats the signalling.
It is also the mechanism the GLP-1 medicines borrow. They amplify a satiety signal the body already uses, which is why they reduce intake without requiring the patient to try harder.
Dieting works against you here, because falling body fat reduces leptin and hunger signalling rises. That is normal physiology rather than failure, and it is the argument for moderate deficits, high protein and enough food volume to keep meals feeling like meals.
In practice, build meals around protein and fibre, favour food you have to chew, and use our protein intake calculator to set the target that does most of the work.