Gavin Rhett

I am a teenager. I exercise and I like to eat healthy food. I live at home with my parents and they eat nothing but junk food. They are the food providers. They buy very little healthy food.
They buy mostly Little Debbie snacks, potato chips, ice cream, hot dogs, pop, bags of candy, cake mix, etc.
They sometimes buy healthy food, but only a small percentage of the food budget is allotted to healthy foods (eg. fruits, vegetables, whole grain bread, nuts, etc.).
I want to eat only healthy food, but I'm forced to eat junk food because there is often nothing else to eat. I eat either eat junk food or starve.
I lecture them and try to persuade them to buy healthy food, but it doesn't sink in. They're unreasonable. They give lame excuses like, "We can't afford it". We certainly can afford it, the only reason they can't afford it is because there's not much money left after all the junk food is purchased.
How can I persuade them to spend all or at least a greater portion on healthy food?