I've actually just watched this on iPlayer. I wasn't surprised to see the 800 calorie option in play, but I was quite surprised they were monitoring for nutritional ketosis.
@mikeyB - I'm not questioning your own preferences for approach, but I imagine tthe rapid weightloss could be quite motivational, in the first instance - especially when some people have tried weightloss regimes in the past, and failed. Success inspires.
I will be interested to see where they "go" after the three weeks they're looking at, because in an ideal world, some of the subjects would likely benefit from trimming off a bit more than a stone. that's not being judgemental or fattist about them. It's reflecting the stats recorded by Dr Moseley.
When I was diagnosed I didn't need to lose much weight, but the losses I did have were very rapid - not deliberately; it just seemed when I swerved the "big carbs" my love handles disappeared. I've not varied by more than +/-2kg since - even with my thyroid throwing itself off a metaphoric cliff. (I did get extremely lucky with that bit though!)