system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do our bodies have a mechanism to detect malnourishment (hunger) but not a strong one to detect overnourishment (obesity)?

Like most people here I'm sure, if I don't eat for like 8 hours I can feel my body telling me that I need to put food in it.  My stomach rumbles, I can get irritable, maybe even light-headded.  I'm pretty sure it's the bodies way of saying "Hey! You're killing yourself!"

But if you believe that excessive eating and obesity lead to a shortened lifespan, why don't our bodies shout across that same message?  I guess you could say that there are some physical signs that can come from being overweight, but they aren't as immediate or strong.  You can be full....but being full won't stop you from gaining weight.
gpt
Well for the majority of human existence being overweight was never an issue. That excess energy was needed to fight off predators. Sugars and foods high in fat contain a lot of energy which releases dopamine, these foods are not easy to come across in nature. Fat is just extra energy for survival or atleast it was.