Is the secret to “beast mode” as simple as fasting?

What happens to the brain (and body) when you abstain from all kinds of food or drink over a specific period of time is quite interesting. You’d think that being hungry would make you grumpy, weak, and unable to even lift a finger. It’s possible especially if you’ve conditioned your mind to feel that way in the absence of food but what really happens is that your body will go on survival mode.