In Berlin, I often ate at Maredo's
, a cheap steak chain restaurant. There are so many branches that, like a MacDonalds, if you ask a local where the nearest Maredo's is, you will probably be directed to one within walking distance. Not only are their steaks reasonably priced (by UK standards) but they have an enormous salad bar with eggs and tuna on offer. The "steak and salad" is an obvious menu choice, but do check out for their Angebot (offer) because it is quite often cheaper to take that and pay for an extra salad.
There are lots of LC German meals available. You just have to say no to the bread and noodles and (heavenly but stodgy) dumplings that come with. They love to give you a free starter salad, and although the sauce is often sugary it does mean you get your veg in. Ask nicely for substitutions of some veg dish for the potato/pasta.
Hidden carbs are not a big deal in their sauces - just a little thickening - but there can be a lot of sugar in anything cabbagy, and that includes salads.
Breakfast is easy; have an egg and some ham and cheese. You can even have berries and yoghurt at many hotels, so bring your own splenda for a real treat if you think you might need it. You could daringly try a little rye bread, depending on how many carbs you are allowing yourself.
Lunch? Go find a supermarket and buy cold cuts and cheese. Cheap and tasty and good. You'll be familiar enough with the look of things to choose according to your taste, I am sure. They like cut-up meat slices in jelly, which is pleasantly spicily fragrant and tasty, but is slightly sugary.
Also, there is great cheap Turkish food to be had. Get yourself to a kebab place and have doner with salad. It's certainly far better than the equivalent in England; leaner and more flavoursome.
Finally, if you have a spare couple of hours, it is well worth it to make a visit to the famous food hall in the KaDeWe
at the Kurfürstendamm (Ku’damm)
. The floorplan is here
. It really is an absoloutely wonderful place.
(As for beer; I think they sell the LC stuff in some supermarkets, but no, the beer is not LC, I'm afraid. Treat yourself to some real stuff on your last night.)
Where are you staying? PM me for more details if you want. I was there just recently for a few weeks, and I am going back later this year.