I'm going to confront my gf about her weight
Obviously you care about your girlfriend, so do you think she has gained too much weight?  Couldn't that be a positive thing if she is happy?
That's a negative!  Her body is so much bigger now.  I don't even know what she eats.
It's okay to be worried about your girlfriend's weight if you think she is unhealthy, but it sounds like you are concerned about the way she looks. It's wrong to confront her about her weight, because this is extremely harmful to her self-image.
If I can change her eating habits, I can help her to look hot.
You are coming at this from the wrong way in that you are looking to change your gf in order to meet your standards of beauty. Allow your gf to look the way she wants and eat what she feels she needs to eat instead of trying to control her.