system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do some people find it hard to eat enough, while others over-eat?

It seems like such a basic function but to me eating three times a day, let alone five, every single day of my life is such a chore. I find it hard to imagine that to most normal people it isn't even something they need to consciously think about.

Is there a reason for such disparity in such a basic human function?
gpt
Leptin sensitivity, insulin sensitivity, ghrelin and other hormones cause different appetite levels for different people. That's an oversimplification but basically leptin is one of the main hormones that puts the "brakes" on hunger.  Thinner people have high leptin sensitivity and therefore recognize feelings of fullness more readily after eating.  Overweight people develop resistance to leptin, leading them to feel hungry for longer.