How do you stay energized during a fast?

I do 18 hour fasts with exercise and I end up feeling so tired. I also have horrible brain fog as well. Is there someone out there that knows how to deal with this or should I just quit fasting and do just a calorie deficit instead? via /r/intermittentfasting https://ift.tt/SZ8lqW3 https://ift.tt/DzFmf4C