Board Thread:The Flash episode discussions/@comment-75.148.114.97-20150401203819/@comment-3481504-20150401210343

It could be the case that he knows a method from his time to null this aspect of super speed, however it can be easily assumed that he eats whole mountains of food in seconds at any time he wants and disposes all of it before anyone notices, and is well quenched when he's interacting with Barry.