My daughter did the same thing at that age (she is now 22 months old). I remember being very frustrated with her and concerned that she wasn't getting enough nutrition. Honestly, the best thing that worked was reducing the number of snacks between meals and making sure she was hungry before attempting meals. I found that I was giving her little snacks all the time, so when I gave her lunch or dinner she wasn't really hungry, and it was more fun to throw the food than to eat it. Also, you might try reducing the amount of food you are putting on her plate, and if she eats it all, you can always give her another round.
Also, my daughter only really did the food throwing thing for about a month before she grew out of it. I know that seems like a long time, but it's not too bad in the grand scheme.
Good luck!