I know what you mean, I did slimming world for 6 months at the start of 2011 and it amazed me that I could eat mugshots, muller lights etc until they were coming out my ears (sorry, 'until satisfied') but heaven forbid I should want some avocado or peanut butter as it would eat up my syns for the entire day. I actually felt worse while doing SW because the 'culture' for want of a better word was to eat things like curly wurlys, pink and white wafers, etc with the syns - although it was *possible* to use syns on more nutritious things, I didn't find myself doing so - and those things (along with chemicalised foods and artificial sweeteners) just don't agree with me. A bit of dark chocolate, though, and I'm a happy bunny.
Your point about 'at least they are getting thin', well, as I have switched to low GI I have found that it's perfectly possible to lose weight whilst eating more natural foods. I know the things that make me either bloat or put on fat (white carbs or too many of the good carbs) and so I avoid those things. I don't lose as quickly as some people on SW do, but I never did, even when I was doing SW.
(haha - you have to love mums sometimes don't you!)