What should I do when he refuses to eat?

I prided myself on having such a good eater but in the past couple of weeks my son (19mths) decided he only wants to eat very little or not at all. This doesn't happen every day or at every meal so I'm sure there isn't an underlining issue. But it's becoming frustrating when I prepare meals only to have him refuse to eat it or throw it on the floor if it's within arms reach. After removing him from the table and trying again later he still refuses. My question is do I keep trying until he actually eats or just skip that meal completely? I know he'll eat when he's hungry but I feel like I'm starving him if he doesn't eat at all. I might have been more prepared on how to handle this issue months ago but like I said he has always been such a good eater. I need some tips and advice on how to handle the situation please and thank you.