the reason for him being ripped is no mystery. He is 130 pounds and just does a lot of cardio. Being 'ripped' is just a matter of maintaining a low body fat % and thats not that hard for a naturally small guy. It also has a lot to do with metabolism and its unlikely that he could put much muscle on his frame either (for the same reason why he has so little fat).
his speed eating capacity is basically a trick (combined with freaky genetics) that he has spent years developing. However he is only the speed eating champion, in terms of sheer capacity there are quite few guys in Japan alone who can out-eat him in terms of sheer capacity (they are regular looking fat guys though). A little known secret of these eating champions is that many of them are actually vomiting and/or passing multiple bowel movements (in specially designed underwear...) in secret. I'm not sure if Kobayashi was ever proven to have been doing either of these but I know other guys have been caught.
