eli5: why is it so difficult to go a week without eating when we have 10s of thousands of calories worth of body fat?
In: 89
People answer the *how* but not the *why.*
Our bodies didn’t evolve in the modern age. Immense food availability is something that’s barely 100 years old, with the invention of producing synthetic ammonia (fertilizer).
Hominids are pretty unique in how pervasively we store fat (though there are others), and much of it comes down to migratory behavior and a very calorie hungry brain. The brain can’t store energy, so the body needs to constantly provide it, via consuming food or tapping into reserves. Way back when, food availability wasn’t constant, so the body developed the insulin response to trigger the rapid storing of blood sugar as body fat when food was plentiful. In later times of sparse food, the body fat would be consumed and converted to a usable form to produce ATP (body’s raw “energy” unit).
So in short, while we may have plenty of fat reserves, there’s no connection between quantity of fat reserves and the instinct to consume, as there would be little to reinforce such a physiological development – those that consumed more had more biological resources and had more offspring.
Latest Answers