My 14 month old does this with his actual food and it drives his Dad and I mental!! However, we've decided that if he's throwing things around, he must be trying to tell us he's no longer interested in eating. We ask him if he's done, with words and a hand action we use, if he doesn't respond, we offer another bite of food. If he refuses this, or tries to toss it we say "Ok, I can see you're done. All done! (w/ hand action)" and we clear away his food, wash hands etc. and excuse him from the table. We continue to eat if we're not done. It's actually been pretty effective and he rarely does it now unless he is genuinely finished. When he does the first throwing of food, we tell him "Don't throw your food, that's rude. Give it to Mommy/Daddy". I'd say 8/10 times, he gives us whatever he no longer wants the next time instead of throwing it. Plus we watch him like a hawk afterwards for him trying to give us something so we can give him praise.
It's hard sometimes, especially because he's not a big eater to start but I try to keep in mind that if he gets two decent meals out of three and has healthy snacks, he'll be ok.
