Over on Scholars and Rogues, there is a blog post entitled, Should we be mean to fat people? You bet.

One thing that the writer claimed was that "Less than 1% of all people have a medical reason for obesity like thyroidism or Cushin’s syndrome."

They referred to an article in WebMD that used to make this claim (but doesn't anymore). I wrote a very long response in the comment, and I'm repeating it here: