College is only 2 or 3 years away, and there will be a salad bar and a vegetarian option at every meal in the dining hall. You can make it. Buy/prep your own food as much as you can in the meantime.

I have some experience watching a parent slowly kill themselves. Trust me when I tell you that he's not oblivious to the harm he's doing, or the cause. He lives in that body. He knows exactly how bad the situation is. You're not gearing up to show him the light here - you would be confronting him with a shame that he's not ready to address, and you're only a child. It's not going to end well. He'll get defensive, and hurt. You'll get frustrated, and hurt.

You can beg and plead all you want for the sake of his health, but until he's ready to change his own habits, you are powerless. Harping on about it will only damage your relationship with your father, and you don't want that. People in the world are rarely going to behave how you want them to, learning to deal with that is part of growing into an adult.

Also, your dad probably thinks that you like poptarts and toaster strudel - that you would find them a treat. Was he aware that you've given those foods up? Does he even realize that you were specifically on a diet this summer? (Teens can change a lot in a short time. If you kept it to yourself, he might attribute the changes to general puberty.) Maybe you could try talking to him more about your interests - your diet - the foods you like. Don't make it about him, make it about you. Maybe you'll find common ground. Worst case, he calls you picky again. Best case, he'll pick you up some grapes or something next time. Maybe he'll even have some.

But yeah, getting snarky with your dad and talking to him like you've got the answers to life is not going to go over well. Good luck, and congrats on your healthy changes.