When I was product testing my children's book Ella's Tummy: A Story of Understand for All Ages -- in other words, having kids read it and tell me what they thought -- one very bright eight year old girl said she thought it was mean that I, as the author, called the main character fat. This was an interesting response, because the book is about fat bullying, and how it is not okay to do it.
ll thoughts about your own body are reinforced. You reinforce stigma in the person next to you, regardless of their size. Your children are taught to see bodies as problematic. And the judgment most certainly does not liberate anyone to live their life with reverence and grace in the body they have.
I don't blame the young man for taking the visual cue of my body and neatly categorizing me with the 5k'ers (which is also a very respectable distance, by the way). Why would he believe that my plus-size body is capable of 21 long kilometres when there aren't any visual cues presented in society to tell us this is possible?