How to get my family to buy healthy food?

I’m sixteen years old and my family is already overweight. Since three weeks ago I’ve notice that I have gained seven pounds. I have always been a healthy eater because I hate unhealthy snack foods (im a cross country runner), but now I find it completely impossible to find anything healthy at my house. The other day my mom went grocery shopping and only* bought, bags of potato chips, little debbie oatmeal snacks, nutty bars, cinn. crackers, moose tracks ice cream, vanilla bean ice cream, cranberry cocktail juice, three liter sprites and diet cokes, lunch meats*healthy though, and tons of cheese its and cheese puffs.
My family is no longer buying regular fruits, everything at my house is canned. only canned Mandarin oranges, peaches and pears. which still is high in sugars and calories and aren’t to healthy to eat.

For tonites dinner my dad went out and bought the whole family burger king. Last night my dad went out and bought taco bell. If I tell my parents I want something healthier instead or i don’t want to eat a large whopper for a dinner they complain and start calling up my other family members saying something is wrong.

My families eating habits are already out of control. I can’t ‘not’ eat; so whatever is at the house I have to munch on. I can’t stand it anymore. The food I am eating has slowed me down at my cross country practices, it has made me depressed and now it is affecting my appearance.

What should I do?