Sounds like my little man he goes through stages, try not to stress yourself and him over it because you cant force him to eat trust me ive tried, (my little man will start gagging.) We live on bread here too!
Only advise I could give that has helped is let him eat when he wants to when he wants to. The struggle at meal times can be to much so let him snack through the day all day its the only way I have managed to keep weight on my cherub. Dont get me wrong I sit him down every breakfast/dinner no distractions and offer a full meal but he just eats the bread and gags on everything else. I do believe its very common of the age and will pass. If your worried he's malnourished the doctor can order blood tests to check, which we did and all his levels were fine just shows its the age and his little body can cope.
Boys!!!!!