You might also look at your work schedule. I've recently become aware of the fact that the tasks that seem to come up during the morning are the ones that are outside of my "sweet spot" from a personality perspective. When those occupy my morning and spend zero time doing things that give me life I end up wiped by lunch regardless of diet or exercise.
That's a good point. When you're really excited about doing something or find it very engaging, it normally does not matter how tired you might be. I say normally here because there are truly times where you are just too wiped out to even do what you enjoy.