Do not give HIM the control. Serve him what you want him to eat, and nothing else. He will catch on. You can make it more enticing by offering a dessert for those who finish everything, but you have to be willing to play hard ball. Start out with small portions, and make sure you start the day with a multivitamin chewable. He WILL NOT starve himself. If you want to make small changes at a time give him some fruit and veggies with something he likes, like pizza or nuggets, but ONLY serve the food he likes once he finishes his fruit and veggies. Also, play around with a VERY WIDE VARIETY of fruits and veggies, served in many ways. We do most of ours raw, but I was surprised to find one of mine likes green beans raw, and another likes zucchini over cooked. The most important part is to stay constant. If you tell him he can have it after he finishes, do not fold. If you offer dessert, even if it is nightly for a while, and tell them they need to eat a good dinner to get it, stick with that.
Also, just a thought, my sister will tell her kids they HAVE to eat 3 bites, I like this premise, however if I am offering a dessert I DO NOT THINK 3 bites is sufficient to qualify for dessert. But make sure portions are reasonable.
I also teach my kids, from VERY EARLY, why it is important. I even have them watch TLC's "Honey, we're killing the kids" when it is on, so they can see that size does not necessarily determine health, and that to be healthy they need to properly fuel their body. I printed up from the internet the many things the differently colors of fruits and veggies give our body, and posted it on the fridge for a while, so they could look at it as they tried all the different fruits and veggies I brought home. And Skippy has a REALLY REALLY good all natural peanut butter. It is still high in fat, but serve it with apples, to encourage them to eat apples. Even with apples, do not assume they like what you do. I have one who likes green apples, and they all prefer them softer.
Also, one of the tacts they you on 'Honey we're killing the kids" is to have them help make the food. It encourages them to eat it, bc they made it. Kids love to try what they have made. Or get a creative cookbook and make it fun to eat, ants on a log for example.
I have slowly employed all of these, and my kids eat well now. There are still things they do not like, but they eat VERY WELL. Good luck, and remember it is worth the small battles, to get them healthier.
(On a side note, you would not believe the results of parents who allow the kids to dictate what they eat, I have a few friends whose young kids, 8,10,11,13, have dangerously high blood pressure and cholesterol, I have even seen a teenager with type 2 diabetes. Pretty scary, and they all feed their kids what the kids want, instead of trying to teach them healthier habits and enforcing it)