It is tough when parents aren't supportive of you or your decisions. I know my mom is like that- Very judgemental and has some serious boundary issues.
That said, the only person in life you can control is YOU. You know you need to be healthier, so do just that, even if you only take smalls steps- Like taking walks once a day for 15 minutes and making sure to eat at least 1 fruit or 1 vegetable with every meal. Tracking your food, as suggested by others, is a fantastic idea, especially if you are doing to see a dietician. Be meticulous- track every sip, nibble, gulp or bite.
Your name is NinjaChic- So Ninja the heck out the this. You might have to do this on your own, without your families approval or assistance. You might not be able to talk to them about this. You may just have to do it. And you can DO IT!
Go out there and be awesome- Because I can tell that you are already.