I think it might be possible to order low-salt meals, although I'd hate to eat the airline's version.

This article has a sales agenda, but explains what happens when flying:
http://www.life-enhancement.com/arti...ate.asp?ID=909

Note that worsened edema could be a sign of diabetes.

Dry facts:
http://www.nlm.nih.gov/medlineplus/e...cle/003104.htm