Apparently your body stores salt all over the place. It's toxic and the body tries to get rid of it as best it can. When you stop eating salt your body twigs and tries to dump all of the salt it has stored away, it takes about six months to get rid of it all.
Years ago we were on a very strict vegi diet, no animal produce or anything. Felt rather odd at first, didn't feel very well, but after a while we felt great. One thing I noticed was that my pee was clear! The body has less junk to try and get rid of if you put less in. Garbage in, garbage out.