I don't have apnea, but I do have a sleep disorder of some sort (don't know what, insurance won't cover sleep study so I can't get one until I get married), but we can rule out apnea and restless leg. Anyway, I get so sleepy that I feel like when it is not under control that it can be a major obstactle. When you are sleepy you are so busy fighting to stay awake that you do what you can- and eating can help you stay awake. Also, for me, when things tend to get out of control in terms of my health I just cannot focus on diet. I feel like I am trying to juggle so many balls allready and not handling that, and diet would just be another thing that would cause me to freak out.
So get the apnea under control and then focus on diet again, I would say. You don't want to set yourself up for failure.