I usually lose about 10 pounds on a 2 week "traveling" canoe trip.  I also become much stronger in my core muscles, I guess from the paddling; and by the end of the trip the packs have gotten to feel lighter too, even tho they are not. ;D
Women have a harder time shedding weight than men, due to our metabolism quirks, so it is great to wear some of it off on a trip.  Lately I have been camping with folks who are in their 70's and 80's and we do not portage and don't cover as many miles and on those trips I do not tend to lose any weight.  :(