Doctor Who Confidential http://bbc.co.uk/i/s0vs1/
At 23:10 and 23:34
"And I thought, 'well she's really good. It's just a shame she's so wee and dumpy.'"
"When she was about to come through to the auditions I nipped out for a minute and I saw Karen walking on the corridor towards me and I realised she was 5'11, slim and gorgeous and I thought 'Oh, oh that'll probably work.'"
I think that there is a strong implication that the deciding factor in Karen's casting was her looks, and that she would have been discounted from the process had she been 'wee and dumpy' . I'm not actually okay with that. I don't know why I should be.
There is the possibility that Moffatt is speaking ironically, but I see little to suggest it. I hope that Doctor Who is not promoting a culture of 'body-fascism' or 'sexism'.