There are a lot of posts from people struggling with SS, as if that is the only way to do Cambridge. This puzzles me as (like a lot of us) I have previously done WW, Atkins, crash diets etc, from which I know that 790 and even 1000 calorie a day diet is looow and you will lose weight.
I try to stay on SS but know that every few days the need to actually eat something will be too great. So, using the motto "failing to plan is planning to fail", I make sure there is something in the fridge like chicken fillets or prawns (if Sainsburys have them on special offer!). When I have a "must eat" day, I have some of this standby protein, mebbe with some salad. None of it is carb heavy, so it doesn't affect ketosis, sure that day I may consume 800+ calories, but that is still very low and the next day I carry on as usual.
In 3 weeks I've lost 16lb (ok I'm a bloke with a lot to lose), but I know myself and if I didn't make these allowances I'd be sure to quit. Using this method I think this is sustainable and will keep me in CD for the long run.
So, to all those who despair when they "break SS", don't! Just accept it will happen and make sure you eat in a controlled way so you can continue on. Remember that Cambridge themselves suggest you prepare for SS by doing 1k or 790 first to get used to the lower calorie levels.
If that makes any sense.
Peter