There is a simple fact about energy that most people who are uneducated in science simply don’t grasp: fuel is just a way of getting energy from the point where it is collected to the place where it’s going to be used.
That is just as true of the liquid hydrogen and oxygen of the space
shuttle as it is of a Kalahari Bushman gathering firewood, or of
uranium being mined, refined, and trucked to a nuclear reactor.

The !Kung system, however, is many times more efficient than the others.  A Few Comments About Energy — for the Scientifically Disadvantaged* ~ Digital Zen