is it the iron? because i've been using a multi without iron for the last 3-4 weeks and been feeling out of energy and not recovering normally. The only reason why I am questioning is because even when I ate the multi with iron, meat use to give me a spark in energy (probably because of the sat. fat in it)...maybe they both contribute in their own way.
To answer your question, i usually feel the increase in energy right after I eat it, if I eat enough...if I don't then I usually eat more until I do feel energy(that was when I ate red meat). Usually it did not take much red meat to energize me.