I struggle with this as well. All I can attribute is that in order for me to feel energy I must eat quite a bit. Every 1-2 hours. (You must be very disciplined about it) It has to include lean meats for protein. I tried getting by with nuts, fruit, light veggies, etc. Doesn't do it for me. Not that its bad, its just like wanting a large fire but only throwing twigs on it and expecting a long lasting burn.
Don't get me wrong. I've got my own issues and miserable struggles. I do not have it all figured out by any means.