http://www.theguardian.com/society/2015/aug/05/obesity-awareness-may-be-causing-overeating-finds-international-study

this is actually talking about the opposite of what my point was, ie that people who are weight-conscious tend to gain more, but the corollary, where not caring leads you to be healthier and stop engaging in stress behaviors (they call out stress eating as the most obvious culprit), still holds true