The documentary was basically about her trying to go from her natural size 8 to a size 4 (US size zero) in 30 days, to show the dangers of crash dieting and the size zero trend. The whole point was that she was not a skinny-gaunt-Posh-type and was doing the diet not because she wanted to become that way, but to show others the dangers of the trend.
I've spoken with my fiancé about just how he can help - by supporting me and not by questioning what I have had to eat or trying to make me eat more. I can understand that it's difficult for him as well though. I have to see how it goes over the next couple of weeks. I have an appointment with a support group in mid-April and they also have groups for family-members etc. I may send him there if they think it's helpful.