Six inch Meatball Marinaras have the salt and fat equivalent of nine packets of Walkers crisps. So a footlong would be the equivalent of eighteen.
(I worked at Subway at the time that information came out - think it was on a TV documentary or something - and we were even sent a brief on what to say to customers if they brought it up... hahaha)
The lowfat subs are fine though. I always have a veggie delight, which is just cheese and salad, on honey oat bread with one of the lower fat sauces. Nom nom nom.