When I met my now husband, his diet consisted of plain American fare - meat and potatoes, heavy, bland Italian (pizza and pasta, that's it), and a lot of junk food. He had a deep fryer that was in constant use. His diet was so poor that the man thought that Taco Bell was Mexican food!
On the flip, I didn't eat any cooked veggies, not much meat, and preferred not to cook at all, which meant a lot of take out.
Over the years, we've devised a system that works for us. Junk food gets eaten after 8pm. Yeah, we're hiders, but seeing The Kid hopped up on artificial stuff is not a pretty thing. To avoid the manic mood swings, we limit the junk food during the day.
We've slowly introduced new foods. And I do mean slowly. My first enchilada attempt for him was based off a Campbell's soup recipe - all ingredients he had had before, just combined differently. Tonight we're having them with my own sauce, shredded beef, and corn tortillas. Slow changes. It took him 8 years to give up the deep fryer completely. 9 to stop using salt on everything.
And we decided that even if we don't like it, a portion needs to go on our plate. It doesn't matter how big, just a portion.
I still can't get him to give up the nasty cereal in the morning, and I'll never eat cooked broccoli, but we have managed to tweak our diets enough that The Kid (10) will eat almost anything and everything.