100g is not too low to be impossible, but still low enough to be aware of what you eat.
Just have your fish/poultry/meat main course with LOTS of veg - I would say at least 2 very big handfuls of veg. They'll fill you up and are cheap. That plus a decent amount of meat/fish/poultry should be more than enough.
Throughout the day you can still eat some carbs, but obviously I understand you want to minimise them.
How about this:
Omelette for breakfast w/ peppers, onions, bacon, mushrooms and some cheese.
or
Poached eggs on mackerel
Snacks:
Nuts/seeds (go for unsalted/unroasted) - where KD suggested they are high in carbs I don't know, per 100g they are typically less than 10g of carbs.
Avocados
Houmus
Cottage cheese / quark
Lunch:
Food doctor pitta (about 25g of carbs)
w/ chicken/ham/meat/salad/tomatoes/whatever you want/tuna/mayo
Or
Large mixed salad (green/red/spinach), with lardons, shredded chicken, couple of hard boiled eggs, toasted pine kernels, avocados, olive oil, balsamic, salt and pepper.
Dinner:
Meat/fish/poultry + a few hundred grammes of veg (broccoli, carrots, green beans, spinach etc...)
That alone will be well under 100g - heck it's probably just about 50g.
Personally I like sweet potato (100g less than 20g) and cous cous (100g around 20g of carbs) to add a little bulk to some foods. You could add that and still be under 100g.
The key is to avoid High GI foods to keep your insulin levels in check, even more importantly it's avoiding refined/processed foods - they'll **** around with your hormones even less.
