I have been eating low-fat/carb/sodium for months now. The food choices are quite limited but it is certainly possible. The number one things I have had to do are 1) I use FitDay PC software to carefully monitor my nutrients. 2) I supplement heavily with psyllium husks. I hate them but they are necessary to keep the carb levels low and still have normal bowel function. and 3) I use a potassium supplement (several a day) and salt substitute (not for flavor, but because it is made of potassium). I even add it to my drinks, effectively turning them into gator-ade. You have to be really careful with potassium supplementation but you can monitor it using software as long as you log everything.
This is even more challenging for me because I am a vegetarian. For protein I I consume protein powder shakes, MediFast foods, eggs, tofu, and a few select low-carb meat substitute products. I eat lots of veggies, but I limit my selection to the lowest carb ones: mostly spinach, Swiss chard, celery, lettuce, broccoli, cauliflower, and kale. Sometimes I have carrots, tomatoes, or cucumbers, but rarely. Occasionally I add shirataki noodles, soy crisps & puffs, and low-carb cereals when I am craving "carbolicious" foods.
I use a lot of PicoPica hot sauce on my foods since it is practically calorie-free adn provides a ton of flavor. I use Walden Farms dressings a lot. Tey are not the greatest tasting dressings on earth, but they are tolerable and add minimal calories. Not sure about their sodium content, though.
I have lost 37 pounds since July 25th using this technique.
PM me for a recipe for protein powder pancakes with 34g protein and only 2g carbs. It is amazing! Fills that need for sweet-carbs, guilt-free. I usually have one for dessert twice a week or so.