There's an unspoken dynamic called the Fat Friend Syndrome.
In some social circles, people are comfortable with the fat person as long as she remains fat. Once the fat friend loses weight and engages in self-improvement, it disrupts the status quo.
Subconsciously, the presence of the fat friend makes some thinner people feel better about themselves and their appearances.
Once you lose weight, several of these thin friends might develop insecure feelings or feel you're in competition with them. When you're no longer fat, you no longer have the dumpy image that instills a sense of security into them.
So, yes, expect the dynamic of your friendships to possibly change with permanence if/when you ever attain your goal weight.
http://brittanyherself.com/cgg/im-the-fat-friend/