I've just logged back on and I'm staggered by the support and advice my post has received, so first of all a big THANK YOU to everyone.
I've done my total daily energy expenditure and it comes in at 3431 (150kg, 5'11", no exercise, 24yo), which seems very high, especially as I must be eating more than that to be gaining weight. So that would mean 25% of my TDEE would be 857 calories.
I have to admit I failed again today, I've ended up eating about 1500 calories. I think I'll try for 857 next time (Wednesday probably) and over a week or two try to reduce it to a sustainable 600.
Thanks for everyone's advice on how to handle hunger on fast days, I think I'll try to have one large meal of 800ish calories on my next (first I guess) fast day and see how it goes. I'll probably try to remind myself throughout the day that if I eat now I'll have to have a smaller meal later on.
Thank you again everyone for your help and support, this site is fantastic!
I'm curious as to whether people think that they'll be able to keep up this 'diet' for the rest of their lives?
Kronic