Here’s a surprise: the human brain consumes 20% or more of the calories of a typical person. There is evidence that for brain-intensive work, it goes even higher. When you realize that just three or four calories can produce a giant flame (skip to 2:40) we are talking serious energy behind every thought you think. In fact, dealing with the heat load from the brain was a major bottleneck in human evolution.
Let me state this a different way. Nature has decided that for every human that the planet supports, at least twenty percent of the food energy we can scrape together is going to go to information processing — planning, remembering, analyzing, communicating — rather than actually doing stuff. And this is before we spend a dime on technology, not to mention consultants and other brain workers whose bodies aren’t used that much.