Thanks for all the replies so far... they do sound similar in character to my husbands situation.
I realise that I made an error in the initial post. I should have said that he has been on HT for 7 months, not 17. A slip of the finger when typing.
So far with careful eating (healthy eating not starvation), and wise drinking (now that's a bummer), he has managed to lose 2 kg and stay there. He would like to lose another 3-4 kgs.
Thanks again, and cheers