Superman eating Earth food might have less to do with survival than we think.
A Kryptonian under a yellow sun already has access to an enormous energy source, yet Clark still eats breakfast, grabs burgers and sits down for family dinners like everyone else.
Maybe the food provides some biological value. But perhaps the bigger reason is much simpler: Clark Kent eats because Superman may be Kryptonian by birth, but living like a human is the life he actually chose.