I think all parents go through this at one point or another!!
My 5yr old son did this when he was about three. My mom gave me excellent advice (as always!). She has raised five kids of her own, and did daycare in our home for several kids when I was growing up - so I tend to listen to her advice.
That being said, Ignore him.
She said that at that age, children are learning independence, and they are learning that they can get under your skin if they want to. A child will NEVER willingly starve him/herself. Serve nutritious meals for all meals and snacks. if he doesn't eat it, don't make a big deal out of it - the more he sees that he can control your mood/actions by refusing to eat, the more he will do it. I do enforce the "you have to eat one bite" rule, but I also try to make sure that at least one of the foods served is something I know he likes. My son NEVER ate spagetti sauce, for example, until a few months ago. I put it on his pasta everytime I make it. I did bend and bribe him - if he ate two bites with sauce he could have plain pasta (it wasn't an additional food or meal, so I didn't feel too bad about the bribe). Eventually, he started eating the sauce and now he likes it.
Another mom mentioned that you have to introduce something to a child upto 30 times before they have a taste for it-- and this is SO true! My son still wont really eat anything that looks "messy" - casseroles, stews, etc. I serve it anyway, and figure he'll be hungrier at the next meal. If he doesn't eat it, it's not my belly that will be rumbling later. My son also didn't like the texture of certain foods -- he hates fresh pears but will eat canned (he says fresh make his throat itch).
If you are concerned about him getting enough nutrition, you could give him a vitamin supplement. My son seems to like the Centrum Kids. We tried Flintstones and other brands but they were tart, and he didn't like the texture of the gummy vitamins that we tried.
Either way, don't let it get to you. As with everything.... this too will pass :)