Are you implying that you're going to buy khat from a local source. Then sell it to another local source, despite the fact that there's already a cheaper source, and then buy food that is more or less nonexistent locally, and expensive to import by yourself as a person without a warehouse?
If there is already a cheaper source than growing Khat isn't more profitable. Khat is only more profitable if it can be sold for... more profit. That large profit should, assuming the market isn't distorted for other reasons[1], allow you to purchase more food than if you grew the food locally - if that isn't the case then growing food becomes more profitable.
1. I touched on this in a longer sibling comment, but a big reason is artificial supply restriction (as in, sanctions) with continued access to external markets for the black market goods.
Could you please clarify more ? I think I am missing something. If khat pays more wouldn't it mean you can sell khat and buy food with that money ?