As you decrease fruit consumption you need to up the meat consumption. If you try to go zero carb, but replace your carbs with fat instead of meat then you will have less active energy. If you eat lots of meat in the evening and then rest, it will give you active energy for the next day, until you eat again. If you eat fruit throughout the day it will give you active energy. Either way you should have fat for a more sustained balanced energy(even if it's your PRIMARY energy source), but if you try to make fat your sole energy source you will be lethargic as it requires a lot of oxygen to utilise. Your main energy source yeah, but the more you want to have active energy, easy-to-use energy, the more you need to eat of either meat or fruit. ZC is fine, but in an evening meal you should consume lots of meat(lbs), and then rest to allow your body to process it properly, unless you are happy being lethargic. Otherwise you can just eat fruit through the day.
I get the mental aspect. Paleodonk is another who was trying to use fat as almost the sole source of energy, and who felt lethargic as a result. He continued to go through it though because as he said, he didn't 'love himself', so drove on with his present idea of what was dietary perfection, despite the poor way that he felt. In this case, using fat as the sole energy source.
