Health Question.

It looks like you're having a communication issue. Try explaining to your mom and sister that you're trying to avoid fast foods right now and that them bringing it is not helping. Let them know that right now you're concerned for your health and that you'd appreciate it if they didn't bring fast food home for you or even just ate it out where you can't see it. It's good that you're taking control of your health like this, but it's bad to let them brush you off like that. If it seems like they aren't listening you might need to sit them down so all of their attention will be on you. Please fight for yourself, don't let them make compromises. You are concerned about your health from a rational reason and this is a good thing. Remember not to take it too far, while you should be concerned about your health it's bad to get obsessive and insecure. Best of luck!

Explain to them that it is a big deal to you and if they care for you, they will respect your wishes and support you.

Actually it is a big deal and you have to make them understand that. Maybe your mom and sis could also go see a doctor about this issue, so that it could be explained to them by an expert, who'll make them understand how bad this is for the body.