"mitunter" is not current German, more like 19th century. "Manchmal habe ich keinen Hunger." is a better sentence that would not irritate a native speaker.
A reasonably literate native speaker probably would not discuss their intermittent hunger as "now and then"? I like rfo's translation "Manchmal ..."
Are you sure this is the correct translation? "Now and then, I am not hungry."?