Buying food all the time?

Playing as the Ottomans around 1500s. I make a good amount of money. Around 200 gold per month. But no matter how I expand my rgos I always buy food and my market start losing food. Why I am buying food and not the pops? There is enough food in the market but some provinces still imports it. And I cant get that province to positive food because it has no food RGO. So what am I supposed to do?