How come that we can live without food for days, but get hungry within a few hours?
In: Biology
Survival is not thriving. Like you can survive on barely enough food for years, proper nutrition means you can maintain a healthy weight, expend energy on non essential things like exploration and procreation, when you have sufficient food your tribe is more likely to expand. So rather than wait till finding food is a matter of life or death, hunger reminds us to eat frequently, which means in times of plenty we are over nourished for the famine when there isn’t as much to eat.
The hunger response is driven mostly by the hormone insulin.
You eat carbohydrates. This causes your pancreas to release insulin. The insulin helps cells take up the carbs. Now, a couple hours after the meal, the insulin is still up, but the carbs are used up. The insulin tells your body to be hungry.
Meanwhile, if you wait for the insulin to decrease in your blood, it stops telling you to be hungry. Fast forward to day three of starving. No insulin in blood, not hungry!
This is actually the ‘trick’ for why low carb diets help you lose weight. No carbs in diet? No insulin response, no hunger, eat less.
Hunger is your body’s way to say it can physically take more food, not that you’re going to die if you don’t eat.
In the past, or now if you’re poor, it would be disadvantageous to ever pass up food if you can physically take more because you don’t know when your next meal will be. So you get hungry much more often than you *have* to eat.
Hunger is a sensation caused by activity of stomach muscles. It just tells you that your stomach is empty, which usually happens about three hours after feeding. Most of the time it has no bearing on energy needs, that’s why fat people can still feel hungry, while sick people who desperately need nutrition can feel full.
Humans have also developed various feeding habits. The brain adapts to this and suppresses those feelings when it’s inappropriate and brings them back when it seems appropriate e.g. those who eat once a day feel hungry at around the time they usually eat; when you see food, get home, walk by a restaurant, or see pictures of food you suddenly feel hungry.
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