I’ve been IF’ing for quite a while then moved on to 48 hour fasting and this week did my first 4 day fast.
My question to all you clued up EF’ers is why do I seem to have more energy when fasting than I do when I’m not fasting and eating regular keto.
Is it psychological or maybe because I’m not carrying the food in my stomach or as I’m thinking more possible a metabolic reason, interested to know.
Think back to the cave man days when there was no food around, we were hyper alerted to our surroundings, we needed to be to watch for predators and hunt food. I believe fasting mimicks starvation in the sense of being super vigilent. Thats my understanding anyway.
If you’re fat-adapted going into a fast, fasting will generally increase your cortisol and speed up your metabolism (up to a certain point, obviously… starving to death does a number on your energy levels 
). As Ava pointed out, it makes evolutionary sense that the folks who were able to successfully hunt when supplies were low were the ones who survived to pass on their genes.
I also think that digestion takes up a fair amount of energy, so you pretty much remove one big job for your body during a fast.
Our bodies secrete more norepinephrine (also called noradrenaline). It cranks us up. 
Average 14% increased metabolism in the 3rd/4th day of fasting.
What Doug said ^^ and more human growth hormone also - anywhere from 100% to much much higher (I have to look that up - but it was absurdly higher)
Think of the phrase “He’s hungry for it” - implies a sharp acute focused response. That is what you’re feeling - minus the actual hunger😀
