In the end, its how much you eat.
You can be thin and eat a diet of only rubbish. But you wont be healthy. You know that.
I have lost weight eating pretty much what I ate before being banded, including some bread. But I didnt eat entirely rubbish - I ate a good healthy base diet and then shoved in a lot of sugary carb foods on top of that. I've personally never had much of a problem with junk foods like Mcdonalds and KFC, I've never overeaten them or craved them unduly. But muffins, cakes, biscuits, that's another story.
So yes, I cut out those foods for the most part, but I do still eat them on occasion. If I go out for dinner, I'm not going to piss fart around ordering sauces to the side and quizzing the staff about whether there's butter in something. I just have what I fancy, and I dont eat a lot of it.
But my basic, everyday diet, what I eat 90% of the time is healthy. Its healthy, but I really dont believe in low carb atkins style diets. I do eat bread and cereals and I eat good amounts of Protein but not HIGH protein. So again, the next person here will tell me diet contravenes all their rules and I'll never lose weight. But I did and kept it off - so it comes down to calories in/calories out, I think.
Post op, I did exactly what I was told to do and ate really healthy foods too. I actually find it really hard to understand how just after surgery you can not be so bouyed up by enthusiasm, hope and determination that you find this period difficult. I found it really very easy. The hard part of wanting bad foods again came a lot later on. But everyone's different I guess. After the post op period, my doc actually HAS no real rules, the m.o. here in Australia tends to be eating a very normal everyday diet but only a lot less of it. Its about integrating the band into normal life, not about a bunch of rules that really swaps overeating for a life of imposed rules.