Bruce Wayne is out all night busting heads. He comes home and gets 3 hours of sleep. Throughout his day, in addition to running Wayne Enterprises, he is working out and training. He wouldn’t have the time to eat regular food even though Alfred cooks for him. He probably eats a specialized DIY version of Soylent with rediculous amounts of calories. It would be the quickest to make and eat.
I get the feeling that the rest of the bat family probably gets by on junk food though. Probably a lot of Big Belly Burger and PBJ sandwiches. Maybe Tim Drake or Damian Wayne would also eat a Soylent-like DIY.
I wonder what real life olympic level athletes eat. I read somewhere that Usain Bolt ate chicken nuggets before becoming the fastest man in the world.