Hi L.,
This is actually a response for a 14 month old I wrote but thought it may start pertaining to your issue in the near future so am sending it.
This is one of the first ways for kids to start 'pushing the envelope' and having some control. As they get older it is great for them to have some say in their diet, gives them a sense of control in their own lives however right now you still need to be in control. What happened with me kids, as the pediatrician recommended, was to put out the healthy food I wanted them to eat, if it landed on the floor it was cleaned up, and no other food was offered. A healthy snack a couple hours later was offered, if it was thrown down then the same thing, clean up and nothing else offered. Let him throw a fit if he wants and probably will for maybe a day or 2 but once they realize they aren't going to be catered to and there is no other food coming their way they will start to eat. My son was very mobile at a year so he had to help do the clean up, big fit but great results within 2 days.
This sounds tough but I learned from helping with my step sons who were completely catered to at meal time that it continues forever if you don't take care of it when they are little. My oldest stepson refused to eat what the rest of the family ate and at his moms had a nanny that would fix him separate meals of whatever he wanted, to this day, he is 27 now, he thinks he should be catered to at meals. My own son who is now 9 eats what we have or if he really doesn't like something new we are having he will fix himself a sandwich.
As he got older, 18 months and up, he started helping with shopping and cooking. He would help pick out the fruit and veggies, learned how to choose which ones were ripe..., he got to weigh them at the store and carefully put them in the cart. At home he helped crack eggs, kids love this and learn to do it well very quickly, he stirred the food and held measuring cups.... He was much more interested in trying the foods we made, was much more likely to try new foods when he had participated. As he got older we talked science, what foods are good for your brain, help your muscles and bones grow strong, how taste buds change and something you didn't like before you may like later and that you have to try something many times before your taste buds start to like it. Kids really respond to the interaction.
Also don't have junk food in the house as a choice. If it's not there they won't learn to like it or ask for it.
Good luck and make it fun!
SarahMM