ELI5 Caffeine - no calories, so where's the energy from?

Caffeine has almost no calories, but seems to give us a burst of energy on its own. Where does the body get this energy from? ... We explain like i'm five! Thank you to the following reddit users whose questions and responses formed the basis of this mini-podcast: hellblazer153, seattlebattles, zombiealpacalips, jinreeko, badresults, heman8400 If you are a r/explainlikeimfive contributor and would like to appear as a guest on future episodes of the podcast, please e-mail us at [email protected]