Related subject
Because dogs digest food much slower than humans (dogs take some 12 to 16 hours to fully digest a meal), I would think (just thinking here - no evidence) that unless a food contained a significant amount of sugars, that a dog wouldn't get much "energy" from a food for a number of hours after eating? I don't know though.
In other words, a dog's energy levels on Saturday, actually come from the food he ate on Friday night, and not from the food he ate on Saturday morning.