Could you live off a diet of white bread and canned soup forever? You're a fan of processed food then — i.e., food that's undergone a special treatment or procedure to change it.
When people are processed, the same rule applies: what goes in is different than what comes out. When the army processes you during recruitment, you enter a long-haired civilian and come out a shaven headed soldier. When the U.S. government processes your citizenship application, you start as an immigrant and come out a newly-minted citizen. Processed: the opposite of natural or original.