Part 1 is here
Now to the related topic of Satiety.
It was not long ago that being pudgy or having a bit of a gut signaled prosperity, and leanness signaled lower class. Now it's the opposite. With incredible food abundance, and with obesity always in the news, funding for nutrition-related studies has grown. So now we know a lot more about how insulin works and about how the three food categories (fats and oils, carbs, and protein) are handled by the body. We are also learning about how hunger and satiety work. It's quite interesting but complicated.
These are "First World issues." In our world of nutritional abundance, recreational, social, and emotional eating, and the constant temptation of food porn, "hunger" often does not denote a need for nutrition except for the skinny, and satiety is often over-ridden by habit, speed-eating, stomach-stretching, delicious foods, sugar-and-carb dosing, and insulin-resistance. That is what it means when overweight people, who have no pressing energy needs at all other than water, vitamins, and minerals, eat hungrily two or three times a day. We term that appetite "false hunger" not because the appetite is not subjectively experienced but because appetite has, for them, disconnected from nutritional need and satiety signals (which are very slow to go into effect). That luxury used to be only for the wealthy.
It's like the flip side of anorexia. Anorexia nervosa is famously difficult to ameliorate, but it is not too difficult for most pudgy or fat people to re-set their bio-psycho-social food-o-stat if they want to. For starters, that entails small portions, plenty of protein to satisfy the hormones, and very slow eating so as not to short-circuit the awareness of the moment at which "That's enough to sustain me, because I don't feel hunger anymore." That way, the "Eat 'til I'm filled or stuffed...now I'm stuffed" effect never has to happen.
In the Western world, "sufficient" can be the stopping point, not "filled." Except Thanksgiving, when feeling ill from getting stuffed with stuffing is expected.
Being too scrawny, with underdeveloped muscle and bone, is life-limiting and unhealthy, but not as life-limiting as carrying excess fat around with its lengthy list of associated ailments. There's no need to carry it on your body, because there's a pizza joint on every corner to prevent sudden death from starvation. Most people, fortunately, make themselves sensitive to satiety signals most of the time so most active adults are neither significantly under- or over-weight.
Obviously, little of this applies to most children and adolescents.
