Well, I took another look at my liter of Fresca the other day and realized it does have sodium, though only 25mg a serving.
I was under the impression it didn't have any, so I thought I should correct myself here.
Of course, again, 25mg is pretty punnie compared with some diet drinks that have 65 to 70mg, but some people can be very sensitive to sodium.
If you notice things like your fingers or feet swelling after a salty meal or an extra few pounds gained in one day, then this could be caused by water weight which could be caused by the salt contained in what you ate.
Us fatand40 folks have enough to deal with when it comes to extra weight. We sure don't need to gain water weight!
(picture from zenandjuice.com)