Courtney, what I read about Glyx diet - and confirmed by a German post to my request
http://forum.lowcarber.org/showthread.php?t=179528
I think Glyx is not so dissimilar to South Beach. I have seen Glyx stuff around, check out their carb and fat counts. I think it might help. The labeling laws aren't as strict so you may have to guess but diet stuff typically has exact amounts.

large supermarkets may be in large department stores (like REAL (pronounced Rae-ahl) or woolworth or Karstadt). I can't believe Frankfurt doesn't have one of those! I also know from my long-ago low fat traditional dieting that Harzer and Limburger are German cheeses known to be low fat - they taste and smell very strong and may not be to your liking. Also, what I miss from Germany is Rotkaeppchen low fat camembert - it comes color coded (green low, blue high fat??/not sure ) - here brie and camembert is always high fat. Get a German to help you - low fat (in contrast to low carb) is established enough that you should be able to ask at the cheese counter which is their lowest fat cheese!

Diet stuff will be in bigger choices in Drogerien (drug stores).