When you are cutting out carbs those contain most of your sodium intake. Protein in itself is not high in sodium. I would suggest staying away from diet drinks, i know they are free from sugar but having the sugar substitute makes your brain crave the sweets. I am viewing this as a way of eating, a lifestyle change not a diet. I have seen how quickly the weight will come back with a couple weeks off the wagon. Good luck and fight through the Keto Flu!!
Sodium is not inherent in protein or carbs, so I don't know what you're talking about there. Protein and carbs are macronutrients, sodium is a micronutrient. I can add 3 tbsp hot sauce to chicken just like I can brown rice, thus increasing sodium intake with no change in calories. If I had to guess The weight probably came back very quickly because you slowed your metabolism down by a significant amount
Folks, weight loss comes from ONE thing: a calorie deficit. The type of diet, macronutrient balance, etc all serves one purpose: to put you in a calorie deficit.
If you're eating no carbs and in a 500 calorie/day deficit, you'll lose weight basically the same as if you were eating no fat in a 500 calorie/day deficit. If you prefer to be able to load up on guac and cheese instead of chips and rice, that's perfectly fine, but it doesn't make it better than any other diet.
MOST importantly: manage your calorie deficit. As in, don't just eat whatever you want because it doesn't have carbs. You also don't want to consume too little, which is very common if you're just following a cookie-cutter program
Also, IMO zero calorie coke/pepsi is f'in awesome when you're dieting. Fills you up, takes care of the sweet tooth, and has no calories. Probably gives you cancer too but what doesn't nowadays