The sodium would affect both feet most likely too.

Have his veins been checked- maybe less circulation in that leg/foot?

That thought just came to me because a family friend had to have plaque build up practically chiseled out of his leg veins.

Alan definitely needs to up his water especially when going to the gym. It will flush out the excess sodium.
The syrup thing is odd..

when he gets home and is ready to relax -probably putting his feet up will curb any swelling?

The circulation is increased at the gym so when he gets home and sits down fluids may pool at the lowest point?

Just a thought-
Have you ever considered a good Naturopathic/homeopathic doctor?
For overall health?
here are a few sites with info-
http://dmoz.org/Health/Alternative/Naturopathy/
http://www.naturopathyonline.com/consutation.htm
It's quite interesting to read about how minute amounts of certain cell salts {not regular salt} can help to rebalanced the body systems.

Works very well in conjunction with MD treatments
http://www.abchomeopathy.com/
http://www.hmedicine.com/news/guide/single/singles/all
http://www.webhomeopath.com/en/jsp/login.jsp