I wouldn't say it's always the case. But in general I've found that people who define themselves by a couple shared interests or beliefs tend to be fat. It's an easy shortcut to boosting one's own self perceived sense of worth. Care about equal rights and you still have to judge yourself on the entirety of your strengths and weaknesses. But if if you're "a feminist" or "a whatever", than you've already reached your goal as a person and can pretty much just stop any kind of self examination. Similar thing with politics, religion, what have you.