Volek et al. recommend purposely adding 2-3 g of sodium per day if you are eating less than 60 g of carbs per day (1-2 g of sodium is mentioned earlier in the book without regard to carb count); this would be ~5 g (5000 mg) of NaCl salt. Note the 1-3 g of salt is in addition to what's naturally in your food. I tend to get 500-2000 mg/day from food, so some days I do get a total of 5000 mg of Na.