Sorry to split the baby on you, Minerva, but would you also be open to having the main character be nonplussed in public yet in private perhaps has some level of concern? Maybe it's a cop out on my part, and it is true that the issue could overrun the plot, but it might also allow the reader to forge a deeper connection with your character to see her in private act in a way that is contrary to what everyone else in the book sees. Best of luck either way!
I like the way Sharon Short uses it in her Josie Toadfern mysteries. The character is about 20 lbs overweight and it's mentioned, much as a woman does when she's trying on clothes or whatever, but it isn't omni-present. It's realistic and great characterization.
What is your motivation to include this factor? Since this is the age of the anti-hero, is weight akin to the protag having a substance abuse problem? I'm not saying like an addiction or disorder, but weight being more of a long-term thing the protag battles with internally.