Baby Weight and food guilt

When I was pregnant with my son, I gained 36 pounds, all of which I have lost in the first two months.  I was at the movies with a friend this weekend and she wanted some popcorn, so I got in line with her to keep her company.  As we were standing there, my nutrionist from the pregnancy saw us and came over.  I immedately started justifying my being in line.  I wasn’t even getting anything for myself, but felt the need to express this.  Weird.  I haven’t ever felt guilty about eating anything in public before, but I have heard that some people who are my size do.  Why do we feel bad about eating the same stuff as everyone else?