If most people in the developed world have excess fat storage, why do our bodies signal hunger after only a few hours after eating?
In: Biology
Because for millions of years, we had no idea when we would eat next. Fat is stored for emergencies, but the body still wants more food to be added so the emergency doesn’t happen.
>If most people in the developed world have excess fat storage, why do our bodies signal hunger after only a few hours after eating?
To get **more** surplus. In an environment where food is scarce eating and metabolizing everything that *can* be eaten increases evolutionary fitness, as the alterntive is to starve and not propagate your genes.
Fat isn’t a “save it for later” thing. Fat is a “oh fuck i’m about to starve to death” thing.
We evolved as wild animals where food was not guaranteed. If you don’t know the next time food will be available, you eat every time you can. And when you can’t get food, the fat you’ve built up keeps you alive a little bit longer.
You have to remember that having _too much_ food is a pretty recent thing. Up until about 150 years ago (in the developed world) most of your life was spent ensuring you had _enough_ food; dying of starvation was a very real possibility if things didn’t go well.
So for a few hundred thousand years, our ancestors had to eat as much as they could whenever food was there because that might be the only food available for a _long_ time. Turning off hunger meant that you didn’t build up the fat reserves that would sustain you through the lean times.
It is only in modern society that the lean times never come, but our bodies haven’t evolved past the instincts that kept us alive for most of human existence.
Evolution takes place over many many generations (think hundreds of thousands) so things like fundamental changes in biology take place of periods like millions of years.
Humans have only really been able to enjoy reliable food access for maybe 5 generations if you live in a Western country? So even for the most advanced economy today, we’re talking in the region of a few hundred years at MOST.
We are designed to take in food fairly quickly when available to build up stores in body fat. And because we have big brains, it takes a lot of energy to maintain it. Nearly 20% of our base energy use and therefore food consumption goes towards keeping our brains working. (and yes our brains keep working even when we sleep)
Your body is tuned to grab the calories while they’re available, because for almost all of history getting enough food was a struggle. Putting on too much weight occasionally is less unhealthy than starving to death because you don’t have enough reserves, basically.
(Trivia: Even with organised farming and so on, only 700 years ago a British writer described the feudal Lord of the Manor as “the man who always has enough to eat”. Whole populations having lots to eat all the time is a VERY recent thing.)
Evolution did not prepare our body for restaurants and supermarkets. Our bodies are designed for foraging, scavenging, and hunting. We are not supposed to have guaranteed meals multiple times a day. Our bodies react like our next meal is never certain so we need to store up when we can find it to prepare for the times when we can’t.
If you eat on a regular schedule, your body starts to anticipate food coming in around that time. So, it starts releasing chemicals for the food digestion process before the food actually gets there.
This is the hunger you feel. It’s not happening because you need food.
That’s why if you feel hungry but can’t eat, you’ll eventually stop feeling hungry. And it’s how people can do intermittent fasting. Your body adjusts to your new feeding schedule, and you stop “feeling” hungry when you used to eat.
Because your stomach is empty. It’s not signaling you have energy deficiency, it’s signaling that there’s room for more.
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