my DD has been like that for months now. she was obsessed with cheese. then after a week or so, no cheese. no matter what kind it was. then we moved onto to oatmeal, then corn, etc.
IMO, adults act that way too. crave something one day and not the next so why should kids be treated differently? he is just starting to realize he likes some things and not others. or like something one day and not the next.
when my DD does that, i'll offer something else until we hit something she is in the mood for. she can't talk very well yet so it's a guessing game most of the time. also, there are times she just doesn't feel like eating. so we wait. my suggestion would be to give choices that are acceptable to you. like if he doesn't want bread then offer something else that would be OK to you if he did eat. i think parents may make the mistake of offering junk food just to get kids to eat.
i wouldn't sweat it. he is a toddler now and will want to start deciding things in his life. if he eats something and that something is healthy enough in your opinion, then he's fine.