I understand food wasn’t always so abundant, and humans were well served to store excess consumed energy as fat for later use. What I don’t understand is why the body keeps storing fat to the point where a person becomes morbidly obese and it puts their entire health at risk. Why isn’t there a point where the body just let’s the extra calories pass through without saving for later?
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Humans did not evolve with unlimited food available effortlessly.
The body is optimized to work in conditions where food is either scarce, or required effort to acquire.
In conditions where a body will overeat without having to spend any energy, the good old strategy backfires, and stored energy limits body’s capabilities.
It actually does do that, the body will reach a point where it can’t add to the fat store and then starts accumulating in organs, as well as being excreted in waste products. ( Fatty liver is one such organ that gets hit.)
However, this eventually leads to organ damage and has an amplification effect, where the body is unable to receive signals to stop ‘needing’ to ingest available nutrients.
Our bodies doesn’t have a way of letting the extra calories pass through it because that has basically only been a necessity for the last 100 years.
From an evolutionary perspective, it likely just never came up, or was rare enough to not be selected for.
We absolutely survived by holding on to calories from more abundant times, so our bodies adjusted to do that. We just (on an evolutionary scale) never has SO much abundance that we’d get morbidly obese, so we never lost the ability to do that, since we never did it!
Would be interesting to see if we do evolve at some point further, such that our appetites or some other mechanism is selected for to keep our weight down.
It is extremely unnatural that we have this much to eat, and do not have to put any energy into getting that food. Your safety mechanism didn’t evolve because too much food just wasn’t a big enough problem in the past.
If the fatness of people in the past had prevented them from procreating, then you would have had natural selection, and this trait could have evolved. But fat people in the past were also wealthy, and if anything they did procreate more than the thin poor people.
If you think of evolution as an intelligent developer (not generally a good idea but it works well enough here), this situation just literally never came up in beta testing.
Now the human model has been released and it’s too late to make modifications (no more or very little selective pressure).
If you look at the way the body is designed, it seems like **the system that signals hunger and feeding is the part that is broken here**.
The system that stores fat seems to be working correctly.
Your question is sort of like asking “why didn’t the car apply brakes when I was pushing on the gas?” We keep shoving an unhealthy volume of food into the system, and wonder why I am getting an unhealthy amount of fat.
We keep drinking fructose sweetened drinks (fructose mostly metabolizes to fat) even though we are not really hungry.
Because the cases of being fat to death are so rare in our evolutionary history they have always been outweighed by selection against not storing enough to death. Regular famine was always a common threat. We just crossed the over abundance threshold for most in the last century. Having said that, if we eliminated concentrated industrial fat and sugar sources and made processed food illegal, you would have to work a lot harder at getting fat. So that’s another factor.
So there are a lot of good answers in this thread already, but I want to add one thing that no one is mentioning: we don’t know that excess fat in and of itself is actually unhealthy.
We know that the things that *lead* to excess fat are unhealthy: lack of exercise, overeating sugary or extremely fatty foods, etc. And we know that people who are fat tend to be less healthy and at higher risk of certain health problems. But we don’t know that the “being fat” is actually the cause of their unhealthiness or just a by product of it.
The reality may be that our bodies don’t have a mechanism in place to stop excess fat from accumulating because excess fat isn’t actually that big of a deal.
Why do people die from old age? Because something else failed before that was an issue.
Most animals advance to the point of breeding. After that point you no longer affect the eco system.
Teeth rot, bones break, infection kills.
Your body never had excess nutrition for most of our history, no mammal did. If you can get excess, store it for later!
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